Phosphorous and boron doping of a-Si-Ge:H alloys and its effect on p-i-n solar cells

The performance of single-junction a-SiGe:H p-i-n solar cells has been optimized by addressing the alloy composition of the n-layer, the importance of the i(a-SiGe:H)/n interface, and the modification of hole transport in the intrinsic layer by low-level boron doping. The dark conductivity of an a-SiGe:H n-layer was about one order of magnitude lower than that of an a-Si:H n-layer, with a difference of 0.092 eV in the activation energy. Devices with an a-Si:H n-layer have superior performance with higher short-circuit current and FF (fill factor). An inverse graded layer at the i/n interface further improves the FF. Low-level boron doping of the i-layer shifts the Fermi level and changes the charge state of the recombination centers, resulting in an improvement in the long-wavelength response of devices. This optimization has led to an a-SiGe:H solar cell with a conversion efficiency of 10.1% for a short-circuit current density of 20.1 mA/cm².