Stability of P-I-N Amorphous Silicon Solar Cells with Boron-Doped and Undoped I-Layers

Boron-doping the i-layer in p-i-n amorphous silicon solar cells improves the device performance when the density of impurities in the undoped i-layer material is high (< 1020 cm-3). While this technique can boost the initial device efficiencies for poor quality i-layer material, our devices degrade faster than devices made with undoped, low impurity i-layer material. We have measured the degradation of photovoltaic parameters as a function of continuous AM1 exposure time for devices with and without B-doped i-layers. For single junction p-i-n solar cells with comparable initial conversion efficiencies (< 7%, area < 1cm2) we find that our devices containing i-layers deposited from gas mixtures containing 2–3 ppm diborane degrade faster than devices containing undoped i-layers. Similar effects are observed when two-junction stacked cells with B-doped i-layers are compared to two-junction stacked cells with undoped i-layers.