Impact of Ultrathin Electron-Selective Contacts on Perovskite–Silicon Tandem Solar Cells

During the development of perovskite–silicon tandem solar cells, the impact of transport layers of perovskite top cells on the short-circuit current density (JSC) has rarely been considered. Here, we report ultrathin electron-selective contacts as new architectures of electron transport layers (ETLs) by decreasing the C60 thickness to 1 nm, where the carrier collection efficiency is proven to be independent of C60 thickness with tin oxide as a buffer layer. Benefiting from the lowest C60 parasitic absorption, the JSC in the tandem device with ultrathin C60 is enhanced by 0.24 mA/cm2. Moreover, to recover the damage from atomic layer deposition on uncovered perovskite surface, we use poly(methyl methacrylate) (PMMA) as a protective layer. Combining ultrathin C60 and PMMA protective layer, an efficiency of 31.70% is finally achieved in tandem solar cells. These findings demonstrate the feasibility of ultrathin ETLs or ETL-free designs for perovskite–silicon tandem solar cells.