Indium oxide buffer layer for perovskite/Si 4-terminal tandem solar cells with efficiency exceeding 30%

Perovskite/Si tandem solar cells (TSCs) present great potential to surpass the Shockley-Queisser limit of single-junction solar cells for further advancing the power conversion efficiency (PCE) of solar cells. However, the fabrication of TSCs usually encounters challenge of selecting suitable sputtering buffer layer (SBL) to prevent the bombardment during the transparent electrode deposition. Herein, we introduce an indium oxide (In₂O₃) buffer layer via e-beam deposition to fabricate semi-transparent perovskite solar cells (ST-PSCs). The optical transmittance and electrical conductivity of In₂O₃ highly depend on the deposition rate. High deposition rate results in high ratio of metallic indium in the film, which causes severe parasitic absorption. A 20 nm-thick In₂O₃ film deposited at lower rate demonstrated high conductivity, transmittance and robust protection during sputtering. A 1.68 eV ST-PSC incorporating this In₂O₃ buffer layer exhibits a champion PCE of 20.20%, demonstrating the excellent optoelectronic and protective properties of In₂O₃. When combined with a Si subcell, the 4-terminal TSC obtains a remarkable PCE of 30.04%. Importantly, the unencapsulated ST-PSC maintained 80% of initial PCE after 423 h of continuous light soaking in N₂. This work has provided a facile and instrumental transparent SBL strategy for perovskite/Si TSCs.