Improvements in stability of amorphous silicon solar cells by using ECR-CVD processing

Abstract

We report on significant improvements in the stability of a-Si:H prepared using an electron-cyclotron-resonance (ECR) plasma chemical vapor deposition process. The p-i-n samples were prepared on stainless steel substrates in a single ECR chamber reactor using a remote, diluted plasma process, with either hydrogen or helium being the diluent gas. The devices had fill factors of about 70%. The stability of the devices was monitored by subjecting the devices to 2× sun illumination from a xenon lamp. We find that the devices prepared using the remote, hydrogen-diluted ECR (H-ECR) process had a stability with a degradation in fill factor of less than 5% over a 900-h illumination time. In contrast, the devices prepared using either He dilution, or with a standard glow-discharge process, were much less stable than the H-ECR devices. The stability of the H-ECR devices is directly related to the improved stability of the material produced using this technique. We have also fabricated tandem a-Si/a-Si solar cells using this technique, and the stability of the tandem cells is also excellent.