Design and fabrication of hydrogenated amorphous silicon germanide solar cells for high end-of-life performance

Triple junction a-Si:H solar cells form an essential component of high efficiency large area photovoltaic modules. During design, attention is paid to maximizing the end-of-life performance of these cells as they show light-induced degradation of efficiency. This thesis identifies the main loss mechanisms in a-Si:H based solar cells and develops engineering concepts to limit their effects with special emphasis on the bottom a-SiGe:H solar cell of a triple junction stack. The numerical model AMPS was integrated into the cell design cycle by a simultaneous examination of experimental and modeling data. It is shown that cell performance degradation is predominantly a bulk phenomena and the losses at the doped/i-layer interfaces are minimal. The np model to predict the end-of-life performance of a-Si:H based cells is developed and verified against experimental data. These results were integrated into the model for optimizing the end-of-life performance of a SiGe:H cells using i-layer Ge grading and microdoping. The computer designed cells were fabricated in a new three chamber PECVD system and the measured cell performance compared well with the predicted performance verifying model reliability. Suitable i-layer microdoping and Ge grading improve cell performance.