High-efficiency (>30%) monolithic perovskite-Si tandem solar cells with flat front-side wafers

Abstract Perovskite-Si tandem solar cells are the most prominent contenders to succeed commercial single-junction Si cells that dominate the market today. Yet, to justify the added cost of inserting a perovskite cell on top of Si, the tandem devices should first exhibit sufficiently high power conversion efficiencies (PCEs). Here, we present two key developments with a synergetic effect that boost the PCEs of our tandem devices with front-side flat Si wafers - the use of 2,3,4,5,6-pentafluorobenzylphosphonic acid (pFBPA) in the perovskite precursor ink that suppresses non-radiative recombination near the perovskite/C60 interface, and the use of SiO2 nanoparticles under the perovskite film that suppresses the enhanced number of pinholes and shunts introduced by pFBPA, while also allowing the use of [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid as a hole transport layer. Integrating a perovskite cell featuring these developments with a Si cell, reproducible PCEs of 30±1% and a certified maximum of 30.9% are achieved for an active area of 1cm2.