Suppressing Bulk and Interfacial Recombination Losses in Sn–Pb Perovskites for Efficient Printable Low‐Bandgap Photovoltaic Devices

Thin films of tin–lead alloyed perovskites are drawing growing attention, mainly owing to their tunable bandgaps in delivering efficient single‐ and multi‐junction photovoltaic devices. The rapid efficiency advancement of Sn–Pb perovskite devices has been dependent primarily on improving the crystal quality of perovskite films via retarding oxidation of Sn 2+ . Herein, it is demonstrated that in addition to obtaining high‐quality Sn–Pb perovskite thin films, reducing nonradiative recombination losses at interfaces is equally important for realizing efficient solar cells. An aromatic amine is first introduced to passivate the grain boundary in printed Sn–Pb perovskite films, which boosts the open‐circuit voltage ( V OC ) of the solar devices from 700 to 766 mV. Further enhancement of the V OC to 814 mV and finally to 837 mV is realized by forming a 2D/3D‐layered heterojunction and doping the hole extraction layer with a polyelectrolyte, respectively, benefiting from the largely suppressed nonradiative recombination losses at interfaces. Eventually, the mixed Sn–Pb perovskite devices with a bandgap of ≈1.27 eV yield a high efficiency of 19.06% and in parallel show improved shelf and light‐soaking stability.