Enhancing the adhesion between self-assembled molecules and perovskites enabled 22.6% efficiency for flexible solar cells

Abstract

Flexible perovskite solar cells (F-PSCs) hold exceptional promise for portable electronics, yet emerging evidence demonstrates that their efficiency and stability are constrained by the weak adhesion between the hole transporting layer (HTL) and the perovskite. Herein, this study strengthens the interfacial adhesion by improving the film properties of the HTL via optimizing the annealing temperature of self-assembled molecules (SAMs). It is found that an optimal annealing temperature enables the formation of a dense SAM with a good coverage on the flexible substrate. By using an asymmetric SAM of (2-(12-phenylindolo[2,3-a]carbazol-11(12H)-yl)ethyl)phosphonic acid (CPP-2PACz), we significantly enhance the interfacial shear strength and induce a slower crystallization process during perovskite deposition, thereby yielding perovskite films with prolonged carrier lifetimes and suppressed nonradiative recombination. As a result, a champion efficiency of 22.6% is achieved for F-PSCs, and the devices retain over 89% of their initial efficiency after 1000 h of continuous operation, along with improved stability under a thermal cycling ageing protocol.