Eliminating Voids and Residual PbI 2 beneath a Perovskite Film via Buried Interface Modification for Efficient Solar Cells.

The commercialization process of perovskite solar cells (PSCs) is markedly restricted by the power conversion efficiency (PCE) and long-term stability. During fabrication and operation, the bottom interface of the organic-inorganic hybrid perovskite layer frequently exhibits voids and residual PbI 2 , while these defects inevitably act as recombination centers and degradation sites, affecting the efficiency and stability of the devices. Therefore, the degradation and nonradiative recombination originating from the buried interface should be thoroughly resolved. Here, we report a multifunctional passivator by introducing malonic dihydrazide as an interfacial chemical bridge between the electron transport layer and the perovskite (PVK) layer. MADH with hydrazine groups improves the surface affinity of SnO 2 and provides nucleation sites for the growth of PVK, leading to the reduced residual PbI 2 and the voids resulting from the inhomogeneous solvent volatilization at the bottom interface. Meanwhile, the hydrazine group and carbonyl group synergistically coordinate with Pb 2+ to improve the crystal growth environment, reducing the number of Pb-related defects. Eventually, the PCE of the PSCs is significantly enhanced benefiting from the reduced interfacial defects and the increased carrier transport. Moreover, the reductive nature of hydrazide further inhibits I 2 generation during long-term operation, and the device retains 90% of the initial PCE under a 1 sun continuous illumination exposure of 700 h.