Greatly improved efficiency and stability of planar perovskite solar cells via BDADI interfacial modification†

Perovskite solar cells (PSCs) based on the SnO₂ electron transport layer have been widely developed due to their exceptional power conversion efficiency (PCE). Nevertheless, current studies on additive engineering to passivate internal defects can only optimize one layer of the device. In this study, 1,4-butanediamine dihydroiodide (BDADI), which has –NH₃⁺ groups at both ends, is creatively introduced between the SnO₂ film and the perovskite film as a bidirectionally modified agent. Hence SnO₂ electron transport and perovskite growth interface optimization are improved at the same time. The –NH₃⁺ groups of BDADI form chemical bonds with SnO₂, reducing the hydroxyl radicals on SnO₂. The energy level alignment at the buried interface is well optimized. Meanwhile, the –NH₃⁺ groups at the other end interact with the uncoordinated Pb²⁺ through ionic bonding, effectively suppressing the residue of excess PbI₂ at the grain boundaries. As a consequence, SnO₂–BDADI-based PSCs achieve a high PCE of 22.17%. In terms of stability, unpackaged modified devices have also been improved. A BDADI-optimized device that is unpackaged retains 84% of its initial efficiency at 25–30% relative humidity in a dark environment after 720 hours.