Development of amorphous silicon based p-i-n solar cell in a superstrate structure with p-microcrystalline silicon as window layer

Single junction p-i-n cells using a p-μc-Si:H layer as the window layer on top of SnO₂:F coated glass have been fabricated. For the first time an efficiency of 9.63% could be achieved for a single junction cell with a truly microcrystalline p-layer in a superstrate configuration. This was possible because of the success in depositing thin (15 nm) p-μc-Si:H layer on top of SnO₂:F coated glass deposited at low power (100 mW/cm²), moderate temperature (160°C) and conventional frequency (13.56 MHz). This has manifested in excellent blue spectral response and short circuit current. However, open circuit voltage and fill factor were critically dependent on the choice of buffer layer at the p/i interface. Computer simulations point out that this can be attributed to the large valence band offset between the amorphous i-layer and the microcrystalline p-layer. The buffer acts as a barrier to electron back diffusion and it reduces recombination in the p-layer. Tandem cells using both n-μc-Si:H and p-μc-Si:H in the tunnel junction showed an efficiency of 9.9% and FF of 0.73. The tunnel junction n-μc-Si:H/p-μc-Si:H needed an oxide interface layer for a good performance. The role of the interface layer may be to increase the tunnel recombination as well as to act as a diffusion barrier to dopants