a-Si/c-Si1−xGex/c-Si heterojunction solar cells

The performance and material quality requirements of thin film a-Si/c-Si_1-xGe_x/Si heterojunction solar cells are investigated by modeling and simulation. The effects of Ge content, Si_1-xGe_x thickness, Si_1-xGe_x lifetime and a-Si/c-Si_1-xGe_x interfacial quality have been studied. The simulations predict that Si_1-xGe_x based thin film solar cells provide a significant increase in solar cell output current for Ge fractions larger than 30%, due to the narrower band-gap and increased absorption. In addition, the efficiency of thin (2μm) Si_1-xGe_x solar cells surpasses that of Si for minority carrier lifetimes larger than 0.5μs. For these 2μm thin layers, simulations predict reduced material quality requirements for Si_1-xGe_x cells, with a clear performance advantage relative to Si based solar cells.