Influence of deposition pressure on p-type a-Si:H window layer doped by trimethylboron for a-Si:H superstrate solar cell in plasma enhanced chemical vapor deposition

Wide bandgap (Eg) p-type window layer is very important for silicon based thin film solar cell to obtain high performance, especially high open-circuit voltage (VOC). In this work, the influence of the deposition pressure on the properties of p-type a-Si:H window layer doped by trimethylboron (TMB) in plasma enhanced chemical vapor deposition (PECVD) was investigated systematically by transmission, Raman, and Fourier transform infrared (FTIR) spectroscopies. As a result, high performance hydrogenated amorphous silicon (a-Si:H) p–i–n superstrate solar cell with VOC up to 927 mV was successfully achieved on Asahi Type-U SnO2:F coated glass. In this case, excellent wide bandgap p-type a-Si:H window layer was fabricated under a mild deposition condition, including a low hydrogen dilution ratio (H2/SiH4) of 20, a relatively high deposition temperature of 220 °C, which was also adopted for the i-layer and n-layer deposition, and a moderate deposition pressure of about 160 Pa. We think it is the compromise between wide Eg and good microstructure quality of the p-layer that brings about the good solar cell performance. Such p-type window layer will be very helpful for the fabrication of a-Si:H solar cell, especially of the cell finished in a single PECVD chamber, due to its mild deposition condition.