Development of close-to-zero damage rear heterojunction stripe contacts and compatible front metallization approaches for hybrid heterojunction solar cells

摘要

A close-to-zero damage rear-side heterojunction stripe contact has been realized using laser ablation, which involves the optimization of (1) laser fluence and (2) wet-chemical damage removal processes. The saturation current density (j_0) values underneath the heterojunction stripe contacts as well as underneath the passivated regions have been extracted using intensity-dependent photoluminescence (PL) imaging and PL image analysis using Griddler AI. Thus the area-fraction and pitch of rear-side heterojunction stripe-contacts can be optimized by means of numerical computer simulation. The measured implied open circuit voltages and extracted saturation current densities of the heterojunction stripe-contacts (j_(0,cont) ≈ 20 fA cm~(-2)) show that close-to-zero damage rear-side heterojunction stripe contacts can be realized under optimized conditions. For the front-side metallization scheme, a low-temperature metallization approach, i.e. light-induced plating thickened by electroplating, is investigated to avoid degradation of the heterojunction layers by conventional high-temperature screen printing. It's demonstrated that plating can achieve comparable efficiencies with respect to conventional screen printing and can be applied directly to hybrid heterojunction solar cells using a rear-emitter configuration. For front-emitter configurations, a thin evaporated metal contact layer may be used as the seed layer for subsequent electroplating.