Improvements in performance and stability of hydrogenated amorphous silicon based p-i-n solar cell structures

Hydrogenated amorphous silicon (a-Si:H) based materials and p-i-n solar cell structures fabricated from glow discharge chemical vapor deposition of silane (SiH{dollar}sb4){dollar} with and without hydrogen dilution are studied. Deposition parameters leading to high quality doped and intrinsic materials are identified, whose optical, structural, and optoelectronic properties are characterized in detail in order to establish standard baseline materials for use in solar cell studies. Results show that a-Si:H materials and their corresponding solar cells fabricated from glow discharge of silane diluted in hydrogen exhibit distinctly different properties than those fabricated from pure silane not only in the initial state but also in the light-induced degradation kinetics and the final degraded state values, which are thermally reversible (the Staebler Wronski Effect). It is found that these 'hydrogen diluted materials and cells' reach a degraded steady state within 100 hours of AM1.5 illumination, whereas 'undiluted materials and cells' exhibit a continuous degradation for times as long as 500 hours. The origin and exact nature of the differences in degradation kinetics between these diluted and undiluted materials are still controversial. However, experimental results indicate that they can be associated with differences in material microstructures as well as distributions and densities of midgap silicon dangling bond defect states including both neutral and charged states.; In 'standard' p-i-n solar cell structures where no additional p/i interface treatments are performed, the roles played by the component layers are identified. It is found that cells incorporating diluted i-layers exhibit higher initial and stable open circuit voltages (V{dollar}rmsb{lcub}OC{rcub}){dollar} than undiluted cells. Contributions to and limitations on V{dollar}rmsb{lcub}OC{rcub}{dollar} from the p/i interface and bulk i-layer regions are identified with results from dark I-V and light intensity dependence of V{dollar}rmsb{lcub}OC{rcub}{dollar} characteristics, which leads to proposed novel 'customized' cell structures to achieve higher and stable V{dollar}rmsb{lcub}OC{rcub}{dollar} by using atomic hydrogen treatment of or highly hydrogen diluted protocrystalline silicon interface layers at the p/i interface. The built-in potentials (V{dollar}rmsb{lcub}bi{rcub}){dollar} in these p-i-n cells are estimated by the saturated values of V{dollar}rmsb{lcub}OC{rcub}{dollar} measured at low temperatures and no limitations on the AM1.5 V{dollar}rmsb{lcub}OC{rcub}{dollar} are found.