Precisely Tuning 3D/Quasi‐2D Perovskite Heterojunctions in Wide‐Bandgap Perovskites for High‐Performance Tandem Solar Cells

Wide-bandgap (WBG) perovskite sub-cells in all-perovskite tandem solar cells (AP-TSCs) suffer from severe open-circuit voltage loss and poor light stability. The formation of 3D/2D or 3D/quasi-2D perovskite heterojunctions can effectively passivate interface defects and optimize energy level alignments at the 3D perovskite/C60 interface, thereby enhancing both the efficiency and stability of perovskite solar cells. Herein, a combined evaporation/solution technique is employed to construct Dion-Jacobson (DJ) 2D or quasi-2D perovskites with uniform-phase distribution on wide-bandgap 3D perovskite substrates. By tuning the n values of the DJ phase perovskites, well-refined WBG 3D/2D or quasi-2D perovskite heterostructures are achieved, which exhibit tunable energy levels and mitigate the non-radiative recombination losses at the WBG 3D perovskite/C60 interface. The devices with the WBG (1.78 eV) 3D/quasi-2D n = 3 perovskite heterostructures achieve the champion power conversion efficiency (PCE) of 20.71% (certified 20.53%). When combined with narrow-bandgap (NBG) perovskite sub-cells, the fabricated 2-terminal AP-TSCs achieve a PCE of 28.99% (certified 28.81%). The tandem device maintains 80% of its initial PCE after 501 h of operation at maximum power point.