Perovskite tandem solar cells with improved efficiency and stability

Tandem solar cells represent an attractive technology to overcome the Shockley-Queisser limit of single-junction cells. Recently, wide-bandgap metal halide perovskites are paired with complementary bandgap photovoltaic technologies (such as silicon, CIGS, and low-bandgap perovskites) in tandem architectures, enabling a pathway to achieve industry goals of pushing power-conversion-efficiency (PCE) over 30% at low cost. In this review of perovskite tandems, we aim to present an overview of their recent progress on efficiency and stability enhancement. We start by comparing 2-terminal and 4-terminal tandems, from the perspective of technical and cost barriers. We then focus on 2-terminal tandems and summarize the collective efforts on improving their performance, fabrication processing, and operational stability. We also present the comprehensive progress in perovskite/Si, perovskite/CIGS, and perovskite/perovskite monolithic tandems, along with advanced technology for subcell diagnosis. We highlight that an in-depth understanding of the mobile ion character of perovskites and applying consensus stability tests (such as the extended ISOS protocol for perovskite) under light, heating, and voltage bias are critically important for improving perovskite tandems toward 25-year outdoor operation lifetime.