Role of Interfaces and Contact Formation for the Application of Lead-Free Perovskite Materials in Photovoltaic Cells

Perovskite solar cells (PSCs) represent a promising approach toward a climate-neutral energy supply. Great progress has been made to reach attractive efficiencies of photovoltaic cells at rather low energy input. However, the toxicity of today ' s most efficient materials combined with their chemical instability even when assembled to devices poses unsolved problems. Alternative materials have been developed but up to now cannot compete in efficiency. In many instances, such lack of efficiency is caused by problems in contact formation. Aside from reports in cell architecture, a number of studies have focused on the specific investigation of contact phenomena, also in lateral geometry. Chemical reactivity at interfaces and migration of ions in contacts and within the perovskite materials lead to significant hysteresis in electron conduction and photovoltaic properties. Herein, recent results on such investigations for lead-free perovskite materials are reviewed. The main findings of contact formation with these materials are summarized and the specific impact of different methods of analysis is discussed. By these means, the hope is to provide a good starting ground for groups with new approaches to materials chemistry or device architecture as well as to groups with new approaches to device analysis.