Transparent conducting electrodes for perovskite–silicon tandem solar cells

Transparent conducting electrodes (TCEs) combine high optical transmittance and electrical conductivity, and are an essential component of tandem solar cells. Although tandem cells offer a pathway to power conversion efficiencies exceeding 40% at low cost, they introduce new challenges for TCE design. Achieving the required balance of optical, electrical and chemical properties has so far limited practical TCEs in tandems to a small set of high-cost, indium-based oxides. Recent advances in computational and experimental techniques have improved understanding of TCE solid-state physics, revealing promising alternative materials. In this Review, we examine the material properties essential for TCEs in perovskite–silicon tandems, evaluate current candidates, and highlight the key challenges and opportunities for next-generation TCE development. Our goal is to bridge the gap between materials science and device engineering, providing a roadmap to accelerate the integration of advanced TCEs in high-efficiency optoelectronic devices. Transparent conducting electrodes are a key performance and sustainability bottleneck in high-efficiency perovskite–silicon tandem solar cells. This Review examines how optical, electrical and interfacial losses in transparent conducting electrodes arise in tandem cells and outlines strategies to enable scalable, low-indium electrodes for next-generation devices.