Electrospun tri-cation perovskite nanofibers for infrared photodetection

Tri-cation (Cs${}^{+}$/CH${}_3$NH${}_3$${}^{+}$/CH(NH${}_2$)${}_2$${}^{+}$) and dual-anion (Br${}^{-}$/I${}^{-}$) perovskites are promising light absorbers for inexpensive infrared (IR) photodetectors but degrade under prolonged IR exposure. Here, stable IR photodetectors based on electrospun tri-cation perovskite fibers infiltrated with hole-transporting π-conjugated small molecule 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9-spirobifluorene (Spiro-OMeTAD) are demonstrated. These hybrid perovskite photodetectors operate at a low bias of 5 V and exhibit ultra-high gains with external quantum efficiencies (EQEs) as high as 3009%, decreasing slightly to ≈2770% after 3 months in air. These EQE values are almost ten times larger than those measured for photodetectors comprising bilayer perovskite/Spiro-OMeTAD films. A high density of charge traps on electrospun fiber surfaces gives rise to a photomultiplication effect in which photogenerated holes can travel through the active layer multiple times before recombining with trapped electrons. Time-resolved photoluminescence and conductive atomic force microscopy mapping reveal the improved performance of electrospun fibers to originate from the significantly enhanced interfacial surface area between the perovskite and Spiro-OMeTAD compared to bilayers. As a solution-based, scalable and continuous method of depositing perovskite layers, electrospinning thus presents a promising strategy for the inexpensive fabrication of high-performance IR photodetectors for applications ranging from information technology to imaging. (© 2022 Wiley‐VCH GmbH)