Confinement‐Driven Bulk Photovoltaic in Lead‐Free Hybrid Perovskite for Self‐Powered X‐Ray Detection

Abstract Lead‐free hybrid perovskites (HPs) are considered as environmentally friendly photodetection materials. However, there are few studies on self‐powered photodetection in lead‐free HPs, and most of them are achieved through the introduction of chiral ammonium cations induced bulk photovoltaic effect (BPVE). Notably, enantiomeric pure chiral ammonium cations are difficult to synthesize, the quantity is small and the price is high. Therefore, choosing achiral ammonium cations to induce BPVE in lead‐free HPs is crucial. Herein, achiral cations 1,3‐bis(aminomethyl)cyclohexane (1,3‐BMACH) is exploited to induce bulk photovoltaic through confinement effect in (1,3‐BMACH)BiI₅, then self‐powered X‐ray detection is successfully realized. Due to the large space in zero‐dimensional (0 D) (MXD)BiI₅ (MXD is meta‐xylylenediammonium), the confinement effect is not obvious, resulting in the disorderly arrangement of MXD²⁺ cations and a centrosymmetry structure of (MXD)BiI₅. Benefiting from the large photovoltage (1.0 V) of (1,3‐BMACH)BiI₅ under X‐ray, its single crystal devices exhibit ultra‐high sensitivity of 170 µC Gy⁻¹ cm⁻² and extremely low detection limit of 49 nGy s⁻¹ under self‐powered mode, which almost surpassing most low‐dimensional single‐phase lead‐free HPs at 0 V bias. This work has promoted the application of lead‐free HPs in the field of self‐powered X‐ray detection.