# Co‐Self‐Assembled Interface Engineering Assisted for Bend‐Resistant and Efficient Flexible Perovskite Solar Cells

## TL;DR

Researchers improved flexible solar cells by using a new interface engineering method that boosts efficiency and durability.

## Contribution

A co-self-assembled monolayer strategy using PNPP and Me-4PACz is introduced to enhance interface properties in flexible perovskite solar cells.

## Key findings

- The device efficiency increased from 21.46% to 23.66% with the new interface strategy.
- The solar cells retained 80% of their efficiency after 10,000 bending cycles.
- PNPP effectively captures PbI2, reducing lead leakage in the device.

## Abstract

Flexible perovskite solar cells (F‐PSCs) have attracted considerable interest for their superior mechanical flexibility. Nonetheless, cryptic bottom‐interface defects hinder further improvements in device performance. Here, a co‐self‐assembled monolayer (Co‐SAM) engineering strategy is implemented by integrating 4‐nitrophenyl phosphate (PNPP) into [4‐(3,6‐dimethyl‐9H‐carbazol‐9‐yl) butyl] phosphonic acid (Me‐4PACz) to improve the NiOx/perovskite (PVK) interface. This technique enhanced the surface uniformity and hydrophilic nature of the NiOx/Me‐4PACz, while promoting favorable growth of PVK crystal orientation. Furthermore, the PNPP effectively mitigates the generation of defects at the NiOx surface and the underlying PVK, ultimately significantly improving the interfacial charge transfer efficiency. Consequently, the efficiency of F‐PSCs rose from 21.46% to 23.66%. Due to better stress distribution within the PVK and stronger adhesion at the NiOx/PVK boundary, the F‐PSCs retained 80% of their original efficiency even after undergoing 10 000 bending cycles. Notably, PNPP exhibited an outstanding capacity to capture PbI2, contributing to the potential for reducing Pb leakage of the device under operational conditions.

In this study, by incorporating 4‐nitrophenyl phosphate (PNPP) into [4‐(3,6‐dimethyl‐9H‐carbazol‐9‐yl)butyl]phosphonic acid (Me‐4PACz), an efficient co‐assembled monolayer (Co‐SAM) is constructed to modulate the bottom interface region, thereby developing highly efficient and stable inverted flexible perovskite solar cells. As a result, we achieved a champion device efficiency of 23.66%, and the device retained 80% of its initial efficiency after 10 000 continuous bending cycles under one‐sun illumination.