In-situ reaction modification of isocyanate derivatives with hole-transport units on perovskite film surface for efficient and stable solar cells

FAPbI3 perovskite solar cells (PSCs) have attracted widespread research attention. The interfacial properties play a crucial role in perovskite defect passivation and interfacial carrier transport, significantly influencing the power conversion efficiency (PCE) and stability of devices. Here, a novel interface modification strategy of in-situ reaction on perovskite surface is proposed. A molecule N,N'-bis(4-isocyanatophenyl)-N,N'-di-p-tolyl-[1,1'-biphenyl]-4,4'-diamine (TPD-NCO), involving a hole-transporting unit TPD was synthesized. The highly reactive isocyanate (NCO) groups addition-reacted with formamidine ions (FA+) from the FAPbI3 surface, forming urea with firm covalent bonds. The resulting stable modification smoothened the interface, and its urea groups coordinated with Pb2+ and formed hydrogen bonds with I-, thereby passivating the surface defects and inhibiting ion migration. Moreover, the hole-transporting units were firstly anchored through this covalent modification as a p-type dopant to lower the interface energy barrier for hole extraction. The PCE of target devices increased from 22.82% to 24.46%, which also remained 93% for 5460 h under high humidity (65% RH), 87% for 1060 h under 75 °C, and 77% for 420 h under maximum power point (MPP) operation at 50 °C, indicating both excellent efficiency and long-term stabilities. This work displays the value of both firm and hole-conductive features in in-situ reactive interface modification.