Monolithic All‐Perovskite Tandem Solar Cells with Minimized Optical and Energetic Losses

Abstract Perovskite‐based multijunction solar cells are a potentially cost‐effective technology that can help surpass the efficiency limits of single‐junction devices. However, both mixed‐halide wide‐bandgap perovskites and lead‐tin narrow‐bandgap perovskites suffer from non‐radiative recombination due to the formation of bulk traps and interfacial recombination centers which limit the open‐circuit voltage of sub‐cells and consequently of the integrated tandem. Additionally, the complex optical stack in a multijunction solar cell can lead to losses stemming from parasitic absorption and reflection of incident light which aggravates the current mismatch between sub‐cells, thereby limiting the short‐circuit current density of the tandem. Here, an integrated all‐perovskite tandem solar cell is presented that uses surface passivation strategies to reduce non‐radiative recombination at the perovskite‐fullerene interfaces, yielding a high open‐circuit voltage. By using optically benign transparent electrode and charge‐transport layers, absorption in the narrow‐bandgap sub‐cell is improved, leading to an improvement in current‐matching between sub‐cells. Collectively, these strategies allow the development of a monolithic tandem solar cell exhibiting a power‐conversion efficiency of over 23%.