Significant improvements in stability of amorphous silicon solar cells by using ECR deposition

The fabrication and stability of p-i-n amorphous Si(a-Si:H) solar cells using low pressure electron-cyclotron-resonance (ECR) discharge are reported. The cells are fabricated at high temperatures (325 to 375 degrees C) on tin oxide substrates using a Hydrogen-ECR discharge. Problems relating to diffusion of B from the p-layer at these temperatures are solved using unique diffusion barriers. High fill factors (68%) have been achieved in these cells using 350 nm thick i-layers in a p-i-n structure. Quantum efficiency (QE) measurements show that the i-layers in these cells have low defect densities and Urbach energies. The ECR cells and companion glow discharge cells with similar initial device parameters were subjected to 200 mW/cm(2) of xenon illumination for 160 h. The tests show that the ECR cells degrade significantly less than comparable glow discharge cells. Detailed measurements of quantum efficiency before and after light soaking show that the improved stability of the ECR cells is due to the more stable i-layer in these cells.