Synergetic substrate and additive engineering for over 30%-efficient perovskite-Si tandem solar cells

Perovskite-silicon (Si) tandem solar cells are the most prominent contenders to succeed single-junction Si cells that dominate the market today. Yet, to justify the added cost of inserting a perovskite cell on top of Si, these 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 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 reliable use of Me-4PACz as a hole transport layer. Integrating these developments in an optically and electrically optimized tandem device (e.g., with a durable Si cell), reproducible PCEs of 30 ± 1%, and a certified maximum of 30.9% are achieved.