OPTICAL MODELLING AND OPTIMIZATION OF SOLAR CELLS WITH NANO- AND MICROPHOTONIC STRUCTURES BASED ON RIGOROUS COUPLED WAVE ANALYSISLOKAR, ŽIGA (Avtor) Krč, Janez (Mentor) Optical modellingphotovoltaicssilicon heterojunction solar cellsRCWACMAThis thesis is focused on the optical simulations of the silicon heterojunction (Si HJ) solar cells. A model based on Rigorous Coupled Wave Analysis (RCWA) was developed and integrated in the so-called Coupled Modelling Approach (CMA). The Si HJ structure consists of a thick crystalline silicon wafer as the absorber, while thin layers of amorphous silicon serve for passivation and selective charge carrier collection to the transparent conductive oxide contacts. Textured silicon wafers with inverted nano pyramids and random micro pyramids were experimentally fabricated at IMEC, Belgium. Some of the wafers were completed to Si HJ solar cells. Primary purpose of the experimental samples was validation and calibration of the developed optical models. The RCWA model was implemented in MATLAB and extended with calculation of local absorption to calculate local absorption in individual layers of the solar cell. After, it was coupled together with ray tracing (RT) and transfer matrix method (TMM) models in the CMA. We show that under certain conditions (number of sub-layers and number of modes) RCWA method accurately simulates structures with nanometer textures, while the CMA is applicable to structures including thin and thick layers, and nano, micro or combined textures. RCWA was extensively analyzed with respect to the number of modes and sublayers required for accurate simulations of textures of different sizes. The P = 900 nm and h = 530 nm textures were found to be efficiently simulated by the RCWA, requiring only 30 sublayers and 3 modes for the inverted pyramid grating, while sine grating required 20 sublayers and 5 modes. Considering the worst-case simulations, 30 sublayers and 5 modes are sufficient for simulations of textures with P = 900 nm and h = 530 nm. Oblique light incidence requires slightly increased number of modes and sublayers. Simulation of P = 1800 nm texture with same aspect ratio was also found possible with reasonable convergence speed and resulting in good efficiency, enabling simulations of structures too large for finite element method (FEM) on current PCs, while requiring wave optics and preventing RT simulations. P = 5000 nm texture, however, was found too large to accurately simulate – convergence was poor, while simulations also showed numeric artefacts. RCWA was applied to partial solar cell structure optimization to improve light in-coupling in Si HJ solar cell. Inverted nano pyramid texture was optimized in simulations by varying pyramid fraction (PF) and found that PF = 1 is the optimal value. CMA was utilized for simulations of complete and encapsulated (PV module) Si HJ structures. Different combinations of front and rear silicon textures were tested first with CMA. Nano/flat texture combination outperformed the rest and offered approximately 0.5 mA/cm2 (1.4%) higher JSC than the commonly used random micro pyramids on both sides. Besides single-side illuminated devices, bifacial PV module was also optimized. In addition to considering different front and rear textures, light management foil (LMF) was applied on top of glass layers. LMF offered significant improvement to the performance of the untextured Si HJ module beyond lowering initial reflectance, while improvements on the textured modules were limited to the lowering air-glass reflectance. Nonetheless, the optimized module with LMF on both sides and micro/nanotexture combination offered 2.63 mA/cm2 (5.6%) higher JSC and thus the conversion efficiency than the one without LMF and micro/micro texture combination. Additionally, for bifacial illumination at albedo α=0.3 at the rear side it had higher JSC than would be theoretically possible with single side illumination.20192019-03-25 11:30:07Doktorsko delo/naloga106891VisID: 45761sl