Dual functional doping with 3-bromopyridine in Spiro-OMeTAD for high-performance and stable perovskite photodetectors

Improving detector performance through simple doping engineering of hole transport layers. • 3-Bromopyridine, as a dual function dopant of Spiro-OMeTAD, can enhance ion transport and passivate defects to achieve the synergistic optimization of transport and stability. • The device is self-powered, the external quantum efficiency of the device is 90%, the dark current density is reduced by two orders of magnitude, the detection rate is increased to 2.77 × 10 13 Jones, and the linear dynamic range is widened to 168.23 dB. Spiro-OMeTAD (2,2′,7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene) is widely used as the hole-transport layer (HTL) in perovskite optoelectronic devices due to its solution processability and favorable material properties. However, undoped Spiro-OMeTAD exhibits inherently low electrical conductivity, necessitating dopants such as lithium bis(trifluoromethanesulphonyl)imide (Li-TFSI) to enhance its charge transport properties. Nevertheless, Li-TFSI possesses strong hygroscopicity and is prone to aggregation within the Spiro-OMeTAD film, which significantly compromises both device performance and stability. To address this challenge, we report a dual-functional strategy that employs 3-Bromopyridine (3-BP) as a dopant to simultaneously enhance hole transport and provide interfacial passivation in Spiro-OMeTAD HTLs. The pyridine nitrogen atom in 3-BP coordinates with Li + ions, weakening Li + –TFSI - interactions and consequently enhancing the mobility of TFSI − anions and the overall film conductivity. Simultaneously, the bromine atom forms halogen bonds with the methoxy oxygen atoms of Spiro-OMeTAD, which strengthens intermolecular interactions and passivates defects. Optimal doping at 2 wt% 3-BP leads to significant performance enhancements: the external quantum efficiency (EQE) increases from 82% to 90%, the dark current density (J d ) decreases by two orders of magnitude (from 7.46× 10 −8 A/cm 2 to 8.71 × 10 −10 A/cm 2 ), and the stability is enhanced, retaining 83.77% of its initial EQE after 500 h of unencapsulated storage in ambient air.