Analysis of p–n Junction Profiles of Polycrystalline Silicon Thin-Film Solar Cells by Electron-Beam-Induced Current Technique

Abstract

The correlation between the p–n junction profiles and photovoltaic performance of polycrystalline silicon (poly-Si) thin-film solar cells deposited by atmospheric chemical vapor deposition is discussed. The p–n junctions were formed by two methods applicable to poly-Si thin-film solar cells, i.e., a conventional solid-phase diffusion process and a low temperature deposition method. The junction profiles were directly observed by a high-resolution cross-sectional electron-beam-induced current technique. The p–n junctions perpendicular to the substrate due to the preferential diffusion of phosphorous atoms along grain boundaries were observed for the high-temperature diffusion process. The perpendicular p–n junction induced the high carrier collection probability through the grain boundaries. The effective carrier diffusion length linearly increased with the p–n junction depth along grain boundaries. In this case, however, the shunt resistance deteriorated due to the carrier recombination through defects at the grain boundaries. The low temperature deposition emitter could suppress the preferential diffusion and then the recombination process through the grain boundaries.