Synergistic Interfacial Engineering With Butylamine Hydrochloride (BACl)-Doped PCBM Enables Four-Orders-of-Magnitude...

Planar perovskite photodetectors are limited by severe interfacial recombination and inefficient charge extraction. Here, we enhance the photoresponsivity of CsPbI₃ photodetectors by four orders of magnitude via incorporating butylamine hydrochloride (BACl) into the PCBM electron transport layer. BACl improves film morphology and conductivity while passivating perovskite surface defects, suppressing non-radiative recombination and optimizing energy alignment. Transient photovoltage and photocurrent measurements confirm the reduced recombination and accelerated charge extraction. The enhancement arises from suppressed recombination and a photogating effect, where trapped holes at the interface create an internal gate that boosts conductivity. Consequently, the champion device achieves a high responsivity of 3.4 A W^{- 1}, a specific detectivity of 4.85 × 10¹² Jones, and a fast response time of 40 µs. Furthermore, the modified device exhibits outstanding operational and storage stability: under continuous 660 nm illumination for 6 h, it shows only a 15.9% fluctuation in the light on-off ratio, vastly outperforming the pristine device (99.5%). After 500 h of storage in a glove box, it retains 48% of its initial photoresponsivity, while the pristine device loses all photosensitivity. This work highlights multifunctional ETL doping as a simple route to high-performance perovskite photodetectors.