CROWM v2.6 User Manual
Contents
1.2. Hide the selected highlighted curve in the current plot 4 6 4 Edit curve button Edit the properties of the selected highlighted curve in the current plot Curve colour and text displayed in the plot legend can be changed as desired 4 6 5 Remove curve button Remove the selected highlighted curve from the current plot 4 6 6 Clear plot button Clear all curves from the current plot 5 DESCRIPTION OF THE INPUT FILES The input files required for a CROWM simulation are located in four input folders In nk Spectrum and Texture In the following each of the input files is explained in detail Please note that additional custom files can be created freely as long as the general structure of the files as explained in the following sections remains unchanged Indeed it is often best and most convenient to use the existing files as templates and simply replace the relevant data and save the file under a new name 5 1 Simulation input files txt located in In folder The input files are located in the In folder of the project folder An input file is a plain text file txt extension which lists all the important simulation parameters such as the structure definition the wavelength range etc The name of the input file can be chosen freely as long as there are no spaces and no non standard characters present in the text For example Sim_Odeg_10percent txt is a valid input file name whereas Sim Odeg 10 t
3. The names of all the output files created during a simulation consist of the name specified in the command e g Out_name followed by different endings e g Out_name_Jsc txt in the case of Jsc files see chapter 6 for a detailed description of the output files 8 Running CROWM from command line 3 2 Running a batch of simulations Batch files are a convenient way for running a series of CROWM simulations Batch files are simple text files with bat extension which contain one or more commands that are sent directly to the command line after the execution of the file Thus extensive series of simulations can be prepared in advance i e a list of commands in the batch file which can then be executed at leisure e g an overnight batch As an example CROWM package includes a batch file called Example_batch bat The file contains execution commands for three example simulations all of which use the same cell structure but different textures applied to the front and back surface of the thick incoherent layer The file can be opened and edited in any text editor such as Notepad The contents of the file are shown in Figure 3 1 echo off echo KKK KKK KKK KK KK KKK KKK KKK KKK KKK KKK KKK KKK KKK KKK KKK KK KK KK KK KKK KKKKKKK echo CROWM v2 6 SIMULATION BATCH FILE echo KAEKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK echo An example batch file for a series of three CROWM simulations echo of the
4. The schematic of the general optoelectronic device structure that can be simulated by means of the optical simulator CROWM is presented in Figure 1 1 The device consists of e A single thick incoherent layer with the thickness in the range of 10 um 10 mm e Optional one dimensional or two dimensional surface textures applied to the top surface and or the bottom surface of the thick incoherent layer The textures at the top and bottom surface do not need to be the same The lateral and vertical features of the textures are in the range of micrometres or larger The textures are assumed to be periodic in both directions see section 5 4 and should be continuous and single valued everywhere i e a single z value per x y coordinate e An arbitrary number of thin films deposited on either or both side of the thick incoherent layer The thicknesses of thin films should be in the range of 1 nm 1 um and are assumed to be much smaller than the lateral and vertical features of the textures As a result the thin films are assumed to be locally flat parallel to each other and the surface of the thick incoherent layer As an option one of the thin films can be treated incoherently e The incident medium typically air and the medium in transmission which are assumed to be infinitely thick incident ray LA O thin film stack top 2D texture Lz Z thick layer y x a bottom 2D texture thin film stack Fig
5. 2 Command Window during a simulation running on a single core Running CROWM using the graphical user interface GUI 13 4 1 2 Simulation batch setup A simulation batch is a series of CROWM simulations which are prepared in advance to be run one after another when required e g an overnight batch Each line in the simulation batch list represents a single simulation The simulations in the batch are executed in order beginning from the top of the simulation batch list A simulation batch can be saved loaded or rearranged as required by using the following controls 4 1 2 1 Open button Open a previously saved simulation batch 4 1 2 2 Save button Save the current simulation batch as a bat file If a simulation batch is saved to the root of the project folder it can be run as a standalone file without using the GUI see chapter 3 for more information about how to run CROWM without using the GUI 4 1 2 3 Remove button Remove the selected highlighted simulation from the simulation batch list 4 1 2 4 Clear button Clear the entire simulation batch list 4 1 2 5 Up button Move the selected highlighted simulation up through the simulation batch list it will be executed sooner 4 1 2 6 Down button Move the selected highlighted simulation down through the simulation batch list it will be executed later 4 1 2 7 RUN button Execute all the CROWM simulations in the simulation batch list using multi
6. 2 1 4 e Incident azimuth angle deg azimuth angle of the incident rays see section 4 2 1 5 e Period of plotted rays period of rays in the ray propagation figure see section 4 2 1 6 5 1 2 Simulation precision parameters e Ray tracing precision level precision level see section 4 2 3 1 e Ray tracing resolution nm ray tracing incremental step see section 4 2 3 2 e Max No of R T events max number of refl trans events see section 4 2 3 3 e Max No of vertical passes max number of vertical passes see section 4 2 3 4 e Max No of horizontal passes max number of horizontal passes see section 4 2 3 5 e Max No of reflections max number of reflections see section 4 2 3 6 e Random number generator seed custom seed for the RNG see section 4 2 2 4 5 1 3 Ray tracing parameters e Number of incident rays X axis number of rays along the x axis see section 4 2 2 1 e Number of incident rays Y axis number of rays along the y axis see section 4 2 2 1 e Ray matrix shift factor X axis shift of the rays along the x axis see section 4 2 2 2 e Ray matrix shift factor Y axis shift of the rays along the y axis see section 4 2 2 2 e Random ray generation randomly generated rays if set to 1 see section 4 2 2 3 e Trace entire thickness trace entire incoherent layer if set to 1 see section 4 2 2 5 e Incoherent ray traced layer index of the incoheren
7. as shown in Figure 5 3 The first block line of numerical data contains the maximum x and y values in micrometres of the texture In the example in Figure 5 3 the texture spans from 0 to 5 um along the x axis and from 0 to 10 um along the y axis The second block of numerical data contains the matrix of z values in micrometres which represents the morphology of the texture as seen from above The origin of the xy plane is assumed to be in the bottom left corner of the matrix The x axis increases from left to right and the y axis increases from bottom to top The matrix of z values must have at least 4 elements in each dimension however the number of elements in both dimensions does not need to be the same The matrix of z values is interpolated to fit across the entire domain as defined by the maximum x and y values During this linear interpolation the data points of the matrix are evenly distributed along each dimension Textures used in CROWM simulations need to be periodic in both dimensions Therefore each value at the right most column of the z matrix should be the same as the value at the left most column in the same row and each value at the top most row of the z matrix should be the same as the value at the bottom most row in the same column This can also be observed in the example texture file shown in Figure 5 3 KKK KKK KK KK KKK KKK KKK KKK KK KKK KKK KKK KKK KK KKK KKK KKK KKK KKK KEK KKK KKK KKK KK KK
8. boundary conditions are applied to the lateral borders of the ray tracing domain i e a ray reaching the left border will reappear at the right border and vice versa as schematically shown in Figure 1 1 e The thin film stacks in the simulated structure are treated by means of fully coherent transfer matrix formalism which is a widely established one dimensional method for simulation of light propagation through a stack of thin layers taking into account coherence effects such as destructive and constructive interference The thin film stacks are assumed to be parallel to each other i e the textures of the thick layers are transferred to all the interfaces within the thin film stacks as schematically shown in Figure 1 1 Since the total thicknesses of the thin film stacks are assumed to be much smaller than the thickness and the texture features of the thick layer the reflected and the transmitted rays through the thin film stacks will always emerge from the same point relative to the local surface where the incident ray impinged upon the thin film stack there are no lateral shifts as also shown in Figure 1 1 In other words infinitely thin thin film stacks are assumed when calculating the location of the reflected and transmitted rays in the incoherent components of the simulated structure Introduction 2 INSTALLATION OF CROWM 2 1 Installation of CROWM program files The optical stimulator CROWM runs on Microsoft Windows
9. set to 1 each ray will be stored if it is set to 2 every second ray along each of the x and y axes will be stored etc Please note that this setting does not alter the number of incident rays which are simulated see section 4 2 2 1 but merely controls the size and density of the ray propagation figure file which is created during the simulation If graphical representation of ray propagation is not required this option should be disabled in order to save disk space 16 Running CROWM using the graphical user interface GUI 4 2 2 Ray tracing parameters 4 2 2 1 Number of incident rays along the X and Y axis text box In a typical CROWM simulation the power of the incident illumination is evenly distributed among the incident rays which are evenly spaced along the x and or y axis also seen in Figure 4 6 This setting controls the number of rays to be generated along each axis Note that the numbers of rays generated along each of the axes do not need to be equal Indeed when performing CROWM simulations of device structures which only include 1D textures i e the texture morphology changes only in one dimension the user is advised to generate rays only along the dimension where the texture morphology changes while keeping the number of rays along the other dimension at this in effect turns 3D simulations to 2D The total number of rays that need to be simulated is one of the critical parameters which significantly affect th
10. INPUT FILES 25 Simulation input files txt located in In folder e ssesssocssocesooessosessesssoee 25 Complex refractive index files nk located in nk folder cccssscssesees 27 Spectrum files spc located in Spectrum folder sccscsssscsssessssesees 27 Texture files txt located in Texture folder sscccssscssssccsssscessssceseeces 28 Simulation batch files bat located in root folder csssscccsssssssccssssccees 29 DESCRIPTION OF THE OUTPUT FILES 31 LOe Ted UO D lt a PEETA SS T a vac oem ee oe ie 31 Reflectance transmittance absorptance files _RTA txt scsssscssssrcesseees 31 Short circuit current density file _JSC tXt sccsssccssssccssssccsssscsssssscsssssssscees 32 Ray propagation figure file _Rays fig cscccssccssssssssssscssssssssessssssseseeesees 32 1 INTRODUCTION 1 1 Short overview The optical simulator CROWM Combined Ray Optics Wave Optics Model has been developed for optical simulation of multi layered optoelectronic structures e g thin film solar cells comprised of a single thick incoherent layer and an arbitrary number of thin coherent layers located on either side of the thick layer The thick layer can be either flat or textured in the latter case arbitrary 1D or 2D textures with lateral and vertical features in the range of micrometres or millimetres c
11. K KKK KKK KK KKK x CROWM v2 6 SIMULATION TEXTURE FILE KKK KKK KKK KKK KKK KKK KKK KKK KKK KKK KKK KKK KK KKK KKK KKK KKK KK KKK KKK KKK KK KKK KKK KKK KK KKK KKK Example triangular texture ATERAL BORDERS OF THE SIMULATION DOMAIN X_max Y_max all dimensions in um TEXTURE MORPHOLOGY at least 4x4 matrix with Z values all dimensions in um Oo te 2 825 1 0 Oo E23 2 10 Of D2 B42 1 0 On M2821 0 Figure 5 3 Data structure of an example texture file Description of the input files 29 5 5 Simulation batch files bat located in root folder Simulation batch files are located in the root of the project folder They are used for running a series of CROWM simulations A batch file is a plain text file with bat extension It consists of a simple header followed by a list of CROWM simulation execution commands see section 3 2 30 Description of the input files 6 DESCRIPTION OF THE OUTPUT FILES The output files created during a CROWM simulation are stored in the Out folder They all have the same basic name defined by the user e g Out_name see section 4 1 1 8 but different endings There are five text files txt extension and optionally one Matlab figure file fig extension generated during each simulation e Out_name_Log txt e Out_name_RTA txt e Out_name_RTA_TE txt e Out_name_RTA_TM txt e Out_name_Jsc txt e Out
12. University of Ljubljana Faculty of Electrical Engineering Laboratory of Photovoltaics and Optoelectronics CROWM Combined ray optics wave optics model User Manual Version 2 6 Ljubljana May 2014 PVC Laboratory of Photovoltaics and Optoelectronics Faculty of Electrical Engineering University of Ljubljana Tr a ka 25 SI 1000 Ljubljana Slovenia http Apvo fe uni lj si Head of LPVO Prof Dr Marko Topi E mail marko topic fe uni lj si Tel 386 1 4768 470 Fax 386 1 4264 630 Author and contact person of CROWM Dr Benjamin Lipov ek E mail benjamin lipovsek fe uni lj si Tel 386 1 4768 845 Official CROWM webpage http Apvo fe uni lj si en software crowm 1 1 1 2 1 3 2 1 2 2 2 3 2 4 3 1 3 2 3 3 4 Contents INTRODUCTION cicsccceci sce sense ettescccepssectvecctacensasccdecestl Short OVERVIEW sciscasecssnccacscicesSnceancabeqoiavecusssacsoedsdeasSuesteadasciaceancadmereussucadagaranabensaceuiande 1 Description of the general simulated Structure ccssssccssssccsssccsssccssssssessescees 2 Description of the optical moOdel sccsssccssssscssssccssssccssssccsssscsssssssssssssssssssoessees 3 INSTALLATION OF CROWM uuu eccsccescceesereee 5 Installation of CROWM program files cssccssssccssssscsssccsssccssscsssssccsssssessessess 5 Installation of the hardware Security Key ccssccssssscssssccsssccssssccssssccsssssssessees 5 Installa
13. XP Vista 7 operating systems It is distributed as a single installation file CROWM_Installer exe located on the installation medium This installation package contains all the necessary program files and folders required to perform CROWM simulations The simulator can be installed to an arbitrary folder on the hard drive e g D CROWM After installation the folder structure within the main root program folder must not be changed in any way although the main program folder itself with all the sub folders and files can be freely copied elsewhere on the system To uninstall CROWM from your operating system simply delete the main program folder with all the contents 2 2 Installation of the hardware security key CROWM is copy protected by means of a hardware security key which needs to be connected to a free USB port during each simulation Before starting to use CROWM the drivers for the hardware security key need to be properly installed on the system The FTDI drivers for the hardware security key are located in the Drivers folder on the CROWM installation medium The same drivers are used for all versions of Microsoft Windows operating system however the installation procedure differs from system to system Therefore to properly install the drivers consult the appropriate installation guide located in the Documents folder on the CROWM installation medium three guides are available for Microsoft Windows XP Vista and 7 op
14. _name_Rays bmp 6 1 Log file _Log txt The log file summarises the most important information about the CROWM simulation It lists any potential errors that occurred during the execution such as missing input data etc stores the names of the input and texture files for future reference and saves the begin end times of the simulation 6 2 Reflectance transmittance absorptance files _RTA txt Reflectance transmittance and absorptance files RTA files in short list the simulated wavelength dependent total reflectance from the device total transmittance through the device and the absorptance within each layer of the device The reflectance transmittance and absorptance are defined as the relative fractions of the incident light power that gets reflected transmitted or absorbed on its path through the structure respectively R Preflecteal Pspc T Piransmittea Pspc A Papsorbeal Pspe Three RTA files are constructed as the result of the simulation one for the TE polarized light one for the TM polarized light and one for the total combined light see section 4 2 1 3 for the definition of polarisation The data structure of an example RTA file is presented in Figure 6 1 31 32 Description of the output files Wavelength nm Rtot A_air A_glass a Ttot 350 0000 0 0186 0 0003 0 0021 atk 0 0000 360 0000 0 0190 0 0003 0 0016 een 0 0000 370 0000 0 0196 0 0004 0 0013 ne 0 0000 Figure 6 1 Data st
15. an be applied on either side of the layer see section 1 2 for a detailed description of the general device structure that can be simulated by CROWM The main input parameters of a typical CROWM simulation are the illumination conditions the exact structure of the simulated device and the optical properties of the materials used in the device The main output parameters are the total reflectance and the total transmittance of the entire device and the absorptances within each of the individual layers see chapters 5 and 6 for a detailed description of the input and output files CROWM is equipped with a fully featured graphical user interface GUI which can be used for running the simulations for viewing and editing the input files for drawing the 3D schematics of the textures and entire device structures and for the analysis and comparison of simulation results see chapter 4 for a detailed description of the GUI features Optionally CROWM can also be run directly from the command line or even from within other programs such as Matlab see chapter 3 The purpose of this manual is to inform the user about the various features and settings of CROWM and at the same time explain how to best utilise the software in order to perform accurate and reliable simulations The user is expected to be familiar with the general topics in optics optoelectronics and photovoltaics 2 Introduction 1 2 Description of the general simulated structure
16. be selected at the top of the menu 4 1 1 7 View button View the selected top or bottom texture in a rendered 3D figure The texture viewer is opened after clicking the button see section 4 3 Running CROWM using the graphical user interface GUI 11 4 1 1 8 Output file name text box Enter the base name of the output files which will be created during the simulation Six output files are created during each simulation all of which have the same base name and different endings see chapter 6 for a detailed description of the output files 4 1 1 9 Browse button Select the base name of the output files by browsing through the previously created output files This is useful if trying to access the results of a previous simulation 4 1 1 10 View 3D structure button View the entire device structure in a rendered 3D figure showing both the top and the bottom texture The device structure viewer is opened after clicking the button see section 4 4 The button is greyed out if no input file is selected 4 1 1 11 View 3D rays button View the ray propagation schematic in a rendered 3D figure The schematic corresponds to the results of the simulation specified by the output name in the output file name text box see section 4 1 1 8 The ray propagation viewer is opened after clicking the button see section 4 5 The button is greyed out if no ray propagation figure file with the specified output name is found in the Out
17. e speed of the simulation Choosing the right number of rays is crucial for obtaining the most information in the least amount of time For this decision the textures of the thick incoherent layer present the most important factor While indeed a single ray is enough to simulate a perfectly flat structure the number of rays generally needs to be increased when the texture becomes more dynamic 4 2 2 2 Ray matrix shift along the X and Y axis check box amp text box In a typical CROWM simulation the incident rays are generated so that the origin of the first ray is located in the 0 0 point of the xy plane By enabling ray matrix shift the rays can be shifted along the x and or y axis by the specified amount 0 1 This value presents the relative shift compared to the full distance between two adjacent rays along the chosen axis 4 2 2 3 Random ray generation check box This setting enables random generation of incident rays which is an alternative to evenly spaced generation along the x and y axis The total number of incident rays is still controlled by the product of the two values specified in the Number of incident rays setting however the location of each ray is determined randomly 4 2 2 4 Custom seed check box amp text box When using random ray generation random number generation RNG functions need to be called By default the initial value seed of the RNG functions is determined automatically at the beginning
18. ength n k nm 300 000 1 530 1 67le 5 305 000 1 530 1 358e 5 1 310 000 530 1 104e 5 Figure 5 1 Data structure of an example refractive index file 5 3 Spectrum files spc located in Spectrum folder Spectrum files are located in the Spectrum folder of the project folder They are used in the simulation to calculate the potential short circuit current densities J from the simulated absorptances in each of the layers see section 6 3 A spectrum file is a plain text file with spc extension It consists of a simple textual header ignored by the simulator followed by two columns of data as shown in Figure 5 2 The first column lists the wavelengths in nanometres at which the spectrum data is given The second column lists the power density in mW cm of each spectral component AM1 5 Spectrum IEC60904 wavelength P nm mW cm2 300 000 3 1430e 3 310 000 0 0653 320 000 0 2043 Figure 5 2 Data structure of an example spectrum file 28 Description of the input files 5 4 Texture files txt located in Texture folder Texture files are located in the Texture folder of the project folder They are used in the simulation to define the texture morphology applied to the top and or bottom surface of the thick incoherent layer A texture file is a plain text file with txt extension It consists of a number of textual headers ignored by the simulator and two blocks of numerical data
19. erating systems During the installation procedure when the installation wizard asks for the location of the drivers simply point to the Drivers folder on the CROWM installation medium Please note that these drivers differ significantly from the official drivers located at the FTDI webpage www ftdichip com the official drivers will not work with the CROWM hardware security key If a communication error with the key should occur at any time during a simulation the event is also logged in the log file see section 6 1 try reconnecting the key and re run the simulation 6 Installation of CROWM 2 3 Installation of the Matlab Compiler Runtime MCR The optical simulator CROWM was written and compiled in the Matlab programming language In order to run CROWM on operating systems which don t have Matlab installed the Matlab Compiler Runtime MCR must be installed in order to provide all the necessary shared functions and libraries required by the simulator The MCR installation file MCR_Installer exe is located in the MCR folder on the CROWM installation medium Before starting to use CROWM MCR needs to be installed to an arbitrary folder on the system After a successful installation reboot of the system is also required Detailed instructions for installing the MCR libraries are located at the official Matlab support page http www mathworks com au help compiler working with the mcr html 2 4 Files and folder str
20. folder of the project folder i e the simulation has not been completed yet or the generation of ray propagation figure files has been disabled see section 4 2 1 6 4 1 1 12 View results button Open the results viewer see section 4 6 By default the results of the simulation specified by the output name in the output file name text box see section 4 1 1 8 are loaded into the simulation results list of the results viewer see section 4 6 4 1 1 13 Add to batch button Add the current simulation specified by the input file the texture files and the output file name to the bottom of the current simulation batch list see section 4 1 2 After adding a simulation to the batch the project folder can no longer be changed it is greyed out Note that all the simulations in the batch must be run from within the same project folder 12 Running CROWM using the graphical user interface GUI 4 1 1 14 RUN button Execute a single CROWM simulation using multiple processor cores After executing the simulation a Command Window is opened displaying the initialisation procedures including the distribution of the load between the processor cores followed by the current status of the simulation The current status of the simulation is given by the index of the current ray in relation to the total number of rays that need to be simulated After the simulation is completed the window is closed Please note that the current sta
21. hown in Figure 4 5 Figure 4 5 An example device structure displayed in the device structure viewer The device structure viewer features the same controls as the texture viewer see section 4 3 except the Open texture file button 22 Running CROWM using the graphical user interface GUI 4 5 Ray propagation viewer Ray propagation viewer is used for graphical representation of ray propagation through the device structure The viewer opens the ray propagation figure file which was created during the simulation see section 6 4 and displays it in the ray propagation viewer window Please note that creation of the ray propagation figure file is controlled by the Period of stored rays setting in the input file see section 4 2 1 6 Propagation of rays through an example device structure is shown in Figure 4 6 Figure 4 6 An example propagation of rays displayed in the ray propagation viewer The following controls can be accessed from the toolbar in the top left corner of the ray propagation viewer e Zoom in Zoom out e Pan Rotate Running CROWM using the graphical user interface GUI 23 4 6 Results viewer Results viewer shown in Figure 4 7 is used for viewing the results of CROWM simulations The basic controls can be accessed from the toolbar in the top left corner e Print prints the contents of the results viewer window e Set plot boundaries used for editing the range of both plot axes e Zo
22. inimum wavelength the maximum wavelength and the wavelength step all in nanometres 4 2 1 3 Polarisation ratio text box Enter the power ratio between the TE polarised and TM polarised incident illumination In the case of purely TE polarised illumination this setting should be set to 1 In the case of purely TM polarised illumination this setting should be set to 0 Global polarisation in CROWM is defined with respect to the horizontal xy plane the electric field of the incident TE polarisation is always parallel to the xy plane the orientation of the coordinate system as assumed in CROWM is also shown in Figure 1 1 4 2 1 4 Incident zenith angle text box Enter the zenith angle in degrees of the incident illumination Zenith angle values in the range of 90 are allowed In the case of perpendicular illumination relative to the horizontal xy plane the zenith angle should be set to 0 4 2 1 5 Incident azimuth angle text box Enter the azimuth angle in degrees of the incident illumination Azimuth angle values in the range of 360 are allowed The origin of the azimuth angle 0 is along the x axis 4 2 1 6 Period of stored rays check box amp text box The check box enables or disables creation of the ray propagation figure file see section 6 4 during the simulation Additionally if creation of ray propagation figure file is enabled the period of stored rays can be entered in the text box If the period is
23. is connected to a free USB port a CROWM simulation can be executed e directly from the command line e g Command Prompt e by means of a batch file or e by using the graphical user interface GUT which is the preferred option When running CROWM from the command line the execution command consists of the simulation execution file either crowm_mce cre for multi core or crowm_sc cre for single core processing followed by four arguments in order e name of the input file e g Input txt located in the In folder e name of the top texture file e g Texture_top txt located in the Texture folder e name of the bottom texture file e g Texture_bot txt located in the Texture folder e name of the output files e g Out_name This is an example command D CROWM crowm_mc cre Input txt Texture_top txt Texture_bot txt Out_name Please note that in the case of flat textures the texture name in the execution command can be omitted and replaced with a single character 0 zero No texture input files are required for specifying a flat texture Following is an example command for a simulation in which the front top surface of the thick incoherent layer is assumed to be flat D CROWM crowm_mc cre Input txt 0 Texture_bot txt Out_name Once the simulation has been executed the status of the simulation is displayed in the command window and the simulation results are stored in the Out folder
24. n limit the number of times that a single ray reflects from the textures If the specified maximum number of reflections is reached the ray is assumed to be absorbed in the vicinity of the texture and the simulator proceeds to the next ray in the analysis Note that in the case of a perfectly flat structure the number of reflections is equal to the number of vertical passes In the case of textured structures however the numbers are no longer the same the ray may experience multiple reflections from a texture before being reflected to the other side of the thick incoherent layer 4 2 4 Structure definition 4 2 4 1 Device structure panel Device structure panel lists the refractive index files used for the layers and their thicknesses in order from top to bottom throughout the device 4 2 4 2 Layer material menu Select the refractive index file which will be used for the layer Refractive index files are located in the nk folder of the project folder 4 2 4 3 Thickness text box Enter the thickness of the layer in nanometres Note that infinite thicknesses are assumed for the incident top medium and the medium in transmission bottom Running CROWM using the graphical user interface GUI 19 4 2 4 4 Insert above button Insert the current layer combination of the refractive index file and layer thickness above the selected highlighted layer in the device structure 4 2 4 5 Replace button Replace the selec
25. of each simulation based on the system clock However by enabling this setting the user has an option to use a custom number for the RNG seed This way if using the same seed in different simulations the same random numbers will be generated and therefore the same results will be obtained Running CROWM using the graphical user interface GUI 17 4 2 2 5 Trace entire thickness check box By default in order to speed up simulations incremental ray tracing between the lowest point of the top texture minimum z value and the highest point of the bottom texture maximum z value is not performed since the thick incoherent layer is perfectly uniform between these two points Enabling this option overrides the default simulation method and forces ray tracing to be performed throughout the thick incoherent layer Note that this setting results in significantly longer simulation times and should only be used when generation of full ray propagation figure file is required see section 6 4 4 2 3 Simulation precision parameters 4 2 3 1 Precision level minimum allowed power ratio text box When a ray with the initial incident power Po is propagating through the device its power P is diminished by numerous refractions reflections and absorption encountered on its path If the power compared to the incident power drops below a certain limit specified by the precision level e g P Po lt 0 0001 or le 4 the ray is ignored and the simula
26. om in e Zoom out e Pan e Legend toggles display of the legend e Open RTA results automatically opens the RTA file in the default text editor e Open Jsc results automatically opens the Jsc file in the default text editor e Open log file automatically opens the log file in the default text editor SIVA OH APO 1 Absorptance in i a SiH Total reflectance 0 9 0 8 0 7 0 6 0 5 0 4 0 3 0 2 550 600 Wavelength nm Simulation results _ _______ Contents of the current plot 2 in A_air Total reflectance 5 m A_glass_Prague Add to plot Hide curve Edit curve A_ITO_SL A_p_a_SiCH_Prague ec Remove curve Clear plot A_TCO_ZnO_u_sputtered Ao Denon Figure 4 7 Results viewer 24 Running CROWM using the graphical user interface GUI The bottom part of the results viewer is divided into two sections The first section is titled Simulation results and lists the reflectance transmittance and absorptance RTA results of the current simulation whereas the second section titled Contents of the current plot lists the selected RTA results which are displayed in the current plot The following controls can be accessed 4 6 1 Add to plot button Add the selected highlighted RTA simulation result to the current plot 4 6 2 Import results button Open RTA results from a previous simulation see section 6 2 4 6 3 Hide curve button
27. on events is reached the ray is assumed to be absorbed in the current medium and the simulator proceeds to the next ray in the analysis 18 Running CROWM using the graphical user interface GUI 4 2 3 4 Maximum number of vertical passes check box amp text box By means of this option the user can limit the number of times that a single ray passes the entire thick incoherent layer from one texture to the other If the specified maximum number of vertical passes is reached the ray is assumed to be absorbed in the thick incoherent layer and the simulator proceeds to the next ray in the analysis 4 2 3 5 Maximum number of horizontal passes check box amp text box By means of this option the user can limit the number of times that a single ray passes horizontally from one lateral border to the other before reaching the top or the bottom texture If the specified maximum number of horizontal passes is reached the ray is assumed to be absorbed in the thick incoherent layer and the simulator proceeds to the next ray in the analysis This setting can also be used as a safety option to prevent a ray becoming infinitely trapped when propagating horizontally within a non absorptive incoherent layer 1 e its power is never reduced below the limit given by the precision level see section 4 2 3 1 Normally such a situation should not arise 4 2 3 6 Maximum number of reflections check box amp text box By means of this option the user ca
28. ple processor cores beginning from the top of the list After running the simulation batch a Command Window is opened displaying the initialisation procedures of each simulation After all the simulations in the batch are completed the window is closed 14 Running CROWM using the graphical user interface GUI 4 2 Input file editor The input file editor shown in Figure 4 3 is used to setup all the parameters of the simulation which are stored in the simulation input file see section 5 1 The full path and name of the input file which is currently being edited by the input file editor is displayed in the text box at the top of the input file editor window To the right of the text box are buttons Open and Save which are used to open a different input file or to save the changes done to the current input file respectively the button Save turns red when any changes are done to the input parameters Input file editor a_SiH_Cell te Se Input file c Program Files CROWM In a_SiH_Cell txt General simulation parameters Spectrum file AM1_5 10nm_step_300nm_1100nm_IEC60904_3 Incident zenith angle deg min step Wavelength range nm 350 10 Incident azimuth angle deg Polarisation ratio TE TE TM 05 W Period of stored rays Ray tracing parameters Simulation precision parameters Number of incident rays along the X axis Precision level min allowed power ratio Number of incident rays along
29. ructure of an example RTA file 6 3 Short circuit current density file _Jsc txt The short circuit current density file Jsc file in short lists the potential J values calculated from the simulated absorptance spectra in each of the layers by applying the illumination spectrum specified by the input file see section 5 3 according to the following equation Iso Boc Atayer A Ada Please note that the J values should be treated merely as indicators of short circuit current gains losses throughout the optoelectronic device Js calculated for a TCO layer for example thus represents the optical losses due to the parasitic absorption in this layer whereas J calculated for an i a Si H layer on the other hand represents the actual expected generated photocurrent assuming that all the absorbed photons contribute to charge carrier generation i e QE A 6 4 Ray propagation figure file _Rays fig The ray propagation figure file is a Matlab figure which contains the structure of the device including both textures superimposed by the trajectories of the rays as they are propagating through the device also shown in Figure 4 6 Only the rays calculated for the last_wavelength of the simulation are included The thickness of each ray segment corresponds to the current power of the ray The generation of ray propagation figure file can be controlled by the Period of stored rays option in the input file see section 4 2 1 6
30. same a Si H solar cell with different glass textures echo on crowm_mc cre a_SiH_Cell txt 0 O a_SiH_Cell_Flat crowm_mc cre a_SiH_Cell txt Triangular txt 0 a_SiH_Cell_Textured_top crowm_mc cre a_SiH_Cell txt 0 Triangular txt a_SiH_Cell_Textured_bot Figure 3 1 Contents of the example batch file 3 3 Running CROWM from other programs The optical simulator CROWM can be run easily from within other applications such as Matlab which makes it fairly simple to implement custom simulation procedures for automatic program execution and optimisation of the simulated structures In the case of Matlab a CROWM simulation can be executed by means of the dos command which sends the string in the argument directly to the command line as shown by the following example dos crowm_mc cre Input txt Texture_top txt Texture_bot txt Out_name 4 RUNNING CROWM USING THE GRAPHICAL USER INTERFACE GUD 4 1 Main simulation panel The main simulation panel which is used to setup and execute CROWM simulations is displayed when running the CROWM exe file in the CROWM installation folder From this panel all the other features of the GUI can be readily accessed by clicking on the appropriate buttons as described in the following The screenshot of the main simulation panel is shown in Figure 4 1 University of Ljubljana C ROW M v2 5 6 Faculty of Electrical Engineering Laboratory of Photovol
31. t layer see section 4 2 4 9 e Incoherent thin layer additional thin incoherent layer see section 4 2 4 10 5 1 4 Structure definition Structure definition consists of two lists the first is the list of layers refractive index files as they appear top down through the device and the second is the list of the corresponding layer thicknesses in nanometres The thicknesses of the incident medium and the medium in transmission are set to 0 All the above settings indicated with an asterisk can be disabled when set to 0 Description of the input files 27 5 2 Complex refractive index files nk located in nk folder The complex refractive index files are located in the nk folder of the project folder They are used in the simulation to define the material of each layer in the analysed structure A refractive index file is a plain text file with nk extension It consists of a simple textual header ignored by the simulator followed by three columns of data as shown in Figure 5 1 The first column lists the wavelengths in nanometres at which the refractive index data is given The second column lists the real refractive index of the material n and the third column lists the imaginary refractive index or the extinction coefficient k for each wavelength A fourth column listing the absorption coefficient a may also be present in the file however it is ignored by the simulator Glass wavel
32. taics Combined Ray Optics Wave Optics Model and Optoelectronics Single simulation setup Simulation batch setup Project folder c Program Files CROWM Input file a_SiH_Cell Top texture file Parabolic Bottom texture file Output file name Results RUN View 3D structure Add to batch Remove RUN single core View 3D rays View results Clear Figure 4 1 Main simulation panel The main simulation panel is divided into two sections The first section is titled Single simulation setup and is used to setup a single CROWM simulation whereas the second section titled Simulation batch setup is used to prepare a series of simulations batch which are to be run in succession 10 Running CROWM using the graphical user interface GUI 4 1 1 Single simulation setup This section is used to setup single CROWM simulations and also access the various other features of the GUI The functionality of the individual controls is explained below 4 1 1 1 Project folder button amp text box Select the current project folder The project folder must contain all the folders required for running a CROWM simulation as described in section 2 4 The user can either browse for the folder by clicking on the button or enter the folder location direc
33. ted highlighted layer in the device structure with the current layer combination of the refractive index file and layer thickness 4 2 4 6 Insert below button Insert the current layer combination of the refractive index file and layer thickness below the selected highlighted layer in the device structure 4 2 4 7 Remove button Remove the selected highlighted layer in the device structure 4 2 4 8 Clear button Clear the entire device structure reverting to the basic device structure comprised of a single glass layer surrounded by air 4 2 4 9 Thick incoherent ray traced layer index text box Specify which layer in the device will be assumed as incoherent and analysed by means of ray tracing Enter the index number of the target layer in the device structure counting top down through the list Note that the incident top medium and the medium in transmission bottom are always assumed to be incoherent 4 2 4 10 Additional thin incoherent layer index check box amp text box If enabled specify a single additional thin layer which will be treated incoherently in the simulation within the framework of the transfer matrix formalism Enter the index number of the target layer in the device structure counting top down through the list 20 Running CROWM using the graphical user interface GUI 4 3 Texture viewer Texture viewer is used for graphical representation of the selected texture If the texture to be
34. the Y axis Ray tracing resolution step nm along the X axis Maximum number of R T events Ray matrix shift along the Y axis Maximum number of vertical passes Random ray generation Custom seed Maximum number of horizontal passes Trace entire thickness 0 Maximum number of reflections Structure definition i i i Insert above air inf A Layer material nk file __ Thickness nm glass 1000000 ITO 70 nm g p_a_SiH 10 nm Thick incoherent ray traced layer index n_a_SiH 20 nm ZnO 80 nm 7 Additional thin incoherent layer index Insert below Ag 300 nm glass 1000000 nm air inf Figure 4 3 Input file editor Additionally the input file editor is divided into four sections each dealing with a specific aspect of the CROWM simulation The functions of the controls contained within each of these sections are explained in the following Running CROWM using the graphical user interface GUI 15 4 2 1 General simulation parameters 4 2 1 1 Spectrum file menu Select the spectrum file see section 5 3 which will be used to calculate the short circuit current densities J from the reflectance transmittance and absorptance RTA results of the simulation The spectrum file must be located in the Spectrum folder of the current project folder 4 2 1 2 Wavelength range text box Enter the wavelength range of the simulation the m
35. tion of the Matlab Compiler Runtime MCR eesssssssesssecssocesoossoosessesssese 6 Files and folder structure of CROWM sssessessesseseesossesoosossesoosoesossossesossossossosossose 6 RUNNING CROWM FROM COMMAND LINE 7 Execution of a single simulation sesssoossooesooccssecssccssocesoossoosssoesssecesocesoosssoesssesssese 7 Running a batch of simulations e sseessecesooescoccssecssecesccesocesoosesoesssecesocesoosssossssesesose 8 Running CROWM from other programs sesssesssccssocesocesoosesoesssecesocesoosesoesssessseee 8 RUNNING CROWM USING THE GRAPHICAL USER INTERFACE GUD esc sccscsctasiccctncecscapassceacsoceteseceasnce 4 1 4 2 4 3 4 4 4 5 4 6 Main simulati n pan l sssssssssssssiseescssseesssssossssssossvsssssssiosssss besss on sonsos asi sovas buns 9 Input file CCUG O Ko sccesscccxesecisdavessescavesdaticeeaseencee aed wend eese ota ee manana 14 Texture VAG WY CN ices sass va gens cee sy cu eucaa euhcev iw seisto dee kosit sarsie teks siod seso rse Ceisiais isror 20 Deyice structure VIC WET ies cdeisusscusesvorcdoscednonssxoscdoaseseseovernsndocnvoeenededoncdentuaccugoatoncesais 21 Ray propagation viewer viscdiveddccccicesvctsdesdacccadesstdssecdecddedadsecsbisdaddeddsiatcsusddssdesesisedontal 22 Re sults VAC WER 2 55555eceseec ca skecbbec esses sesncasesebs cues saseadbascesGeessasecsSouesscescoosas toed ossesseccesoueee 23 5 1 5 2 5 3 5 4 5 5 6 1 6 2 6 3 6 4 DESCRIPTION OF THE
36. tly into the text box By default the project folder is set to the CROWM installation folder 4 1 1 2 Reload button Reload all the input and texture files located in the In and Texture folders of the project folder and list them into the input and texture menus see below This is useful if any changes are made to the input folders e g creating a new input file which would otherwise require a restart of the GUI 4 1 1 3 Input file menu Select the simulation input file from the menu The menu lists all the input files that are located in the In folder of the project folder The menu is empty if no input files are found 4 1 1 4 Edit New button Edit the selected input file or create a new input file if the input file menu is empty The input file editor is opened after clicking the button see section 4 2 4 1 1 5 Top texture file menu Select the texture file from the menu which will be used in the simulation to describe the top texture of the incoherent layer The menu lists all the texture files that are located in the Texture folder of the project folder A perfectly flat surface can be selected at the top of the menu 4 1 1 6 Bottom texture file menu Select the texture file from the menu which will be used in the simulation to describe the bottom texture of the incoherent layer The menu lists all the texture files that are located in the Texture folder of the project folder A perfectly flat surface can
37. tor proceeds to the next ray in the analysis The power of the incident ray Po is defined as the total power given at the current wavelength in the spectrum file see section 5 3 divided by the total number of incident rays Po Pepe A Ninc rays An increased level of precision lower power limit leads to more accurate results however it also leads to dramatically longer simulation times A careful balance thus must be achieved by selecting just the right precision level which will still result in accurate results but won t bog down the simulation to unreasonable durations The setting of 0 001 or le 3 will generally suffice in most cases 4 2 3 2 Ray tracing resolution step text box During a CROWM simulation finite ray tracing steps are employed to incrementally trace the propagation of rays along their trajectories A finer lower ray tracing resolution generally leads to more accurate results however it also leads to longer simulation times Again the most important factor in choosing the right ray tracing resolution is the nature of the textures smaller and more dynamic surface features generally require shorter ray tracing steps finer ray tracing resolution 4 2 3 3 Maximum number of R T events check box amp text box By means of this option the user can limit the number of times that a single ray exhibits reflection or transmission events at an interface If the specified maximum number of reflection transmissi
38. tus of the simulation in the case of multi core simulation is only useful for confirming that the simulation is running It does not however reveal any information about the work done so far since the order of the incident rays that are simulated is chosen randomly each time 4 1 1 15 RUN single core button Execute a single CROWM simulation using a single processor core After executing the simulation a Command Window is opened displaying the initialisation procedures followed by the current status of the simulation The current status of the simulation is given by the index of the current ray in relation to the total number of rays that need to be simulated as shown in Figure 4 2 After the simulation is completed the window is closed B C Windows system32 cmd exe crowm cre a_SiH_Cell txt Periodic_Parabolic txt Periodic_Triangul l Ls progress 5 1156 CWavelength 671156 Wavelength 771156 lt Wavelength 8 1156 lt Wavelength 971156 lt Wavelength 16 1150 CWavelength 11 1150 CWavelength 12 1150 CWavelength 13 1156 CWavelength 14 1156 lt Wavelength 15 1156 CWavelength 16 1156 CWavelength 17 1156 CWavelength 18 1150 CWavelength 1971156 lt CWavelength 20 1156 lt CWavelength 21 1156 lt Wavelength 22 1156 lt Wavelength 2371156 CWavelength 24 1150 CWavelength 25 1150 CWavelength 2671156 lt CWavelength 2771156 lt CWavelength 2871156 lt CWavelength Figure 4
39. ucture of CROWM After a successful installation of CROWM the following sub folders and files can be located in the main program folder e Help this folder contains the User Manual this file Hel oo e In this folder contains the simulation input files see section 5 1 h In e nk this folder contains the complex refractive index files for each layer of the simulated device see section 5 2 aL e Out here is where the simulation results are stored see chapter 6 A Out e Spectrum this folder contains the spectrum files used in the simulations see section 5 3 A Spectrum i ae e Texture this folder contains the files with the description of the _ Texture textures applied to the front and or back surface of the thick incoherent layer see section 5 4 e CROWM exe CROWM GUI execution file see chapter 4 crowm_mc cre e crowm_mce cre simulation execution file for running CROWM simulations on multiple processor cores mc multi core A CROWM exe crowm_sc cre e crowm_sc cre simulation execution file for running CROWM simulations on a single processor core sc single core MCR release 2014a 8 3 32 bit is required to run CROWM v2 6 7 3 RUNNING CROWM FROM COMMAND LINE 3 1 Execution of a single simulation When all the required input data files are present within the corresponding folders see chapter 5 for a detailed description of the input files and the hardware security key
40. ure 1 1 Schematic of the general device structure that can be simulated in CROWM Introduction 3 1 3 Description of the optical model Since the thickness of the thick layer is much larger than the effective wavelength of light incoherent light propagation can be assumed within this layer In the thin film stacks on the other hand layer thicknesses in the range of the effective wavelength of light result in fully coherent light propagation In order to simulate this combined incoherent coherent light propagation CROWM combines two numerical approaches for the optical analysis of the thick and thin components of the simulated structure e Light propagation through the incident medium the thick surface textured layer and the medium in transmission is analysed by means of incoherent three dimensional ray tracing based on geometric optics The incident illumination which can be applied under an arbitrary incident angle combination of azimuth and zenith angles is divided into a number of rays which are then traced through the structure The intensities and the directions of the rays are determined by the texture morphology refraction and reflection effects at the interfaces the optical absorption in the material in the case of absorptive layers and the calculated reflectances and transmittances through the thin film components calculated with a different model see below The textures are assumed to be periodic in which case the
41. viewed contains a large number of data points i e a large matrix in the texture file the texture can be interpolated to a maximum of 200 x 200 points before being plotted in the texture viewer An example parabolic texture displayed in the texture viewer is shown in Figure 4 4 YAO D B A Figure 4 4 An example parabolic texture displayed in the texture viewer The following controls can be accessed from the toolbar in the top left corner of the texture viewer in order from left to right e Zoom in e Zoom out e Pan e Rotate e Open texture file automatically opens the texture file in the default text editor e Save figure save the figure as a bitmap file e Set the point of view along the x axis view the texture in the yz plane e Set the point of view along the y axis view the texture in the xz plane e Set the point of view along the z axis view the texture in the xy plane Running CROWM using the graphical user interface GUI 21 4 4 Device structure viewer Device structure viewer is used for graphical representation of the entire device structure including both textures at the front and back side of the thick incoherent layer If any of the textures contains a large number of data points i e a large matrix in the texture file the texture can be interpolated to a maximum of 200 x 200 points before being plotted in the device structure viewer An example parabolic texture displayed in the texture viewer is s
42. xt is not The contents of the input files can be most conveniently edited by means of the Input file editor window of the CROWM GUI see section 4 2 Alternatively they can also be edited in a standard text editor e g Notepad The input files are divided into four sections e General simulation parameters e Simulation precision parameters e Ray tracing parameters e Structure definition IMPORTANT The structure of the input files must not be changed in any way All the spaces titles and empty lines must remain at their original position The editable parameters in the first three sections must always begin on the 35 column In the following the function of each of the settings in the input files will be explained Where applicable the user will be referred to section 4 2 where these settings have already been explained for the case of Input file editor of the CROWM GUI 25 26 Description of the input files 5 1 1 General simulation parameters e Spectrum file name of the spectrum file see section 4 2 1 1 e TE TE TM ratio polarisation ratio see section 4 2 1 3 e Wavelength start nm minimum wavelength of the simulation see section 4 2 1 2 e Wavelength step nm wavelength step in the simulation see section 4 2 1 2 e Wavelength stop nm maximum wavelength of the simulation see section 4 2 1 2 e Incident zenith angle deg zenith angle of the incident rays see section 4
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