A Self‐Powered UV Photodetector With Ultrahigh Responsivity Based on 2D Perovskite Ferroelectric Films With Mixed Spacer Cations

Abstract Self‐powered photodetectors (PDs) have the advantages of no external power requirement, wireless operation, and long life. Spontaneous ferroelectric polarizations can significantly increase built‐in electric field intensity, showing great potential in self‐powered photodetection. Moreover, ferroelectrics possess pyroelectric and piezoelectric properties, beneficial for enhancing self‐powered PDs. 2D metal halide perovskites (MHPs), which have ferroelectric properties, are suitable for fabricating high‐performance self‐powered PDs. However, the research on 2D metal halide perovskites ferroelectrics focuses on growing bulk crystals. Herein, 2D ferroelectric perovskite films with mixed spacer cations for self‐powered PDs are demonstrated by mixing Ruddlesden–Popper (RP)‐type and Dion–Jacobson (DJ)‐type perovskite. The (BDA_0.7(BA₂)_0.3)(EA)₂Pb₃Br₁₀ film possesses, overall, the best film qualities with the best crystalline quality, lowest trap density, good phase purity, and obvious ferroelectricity. Based on the ferro–pyro–phototronic effect, the PD at 360 nm exhibits excellent photoelectric properties, with an ultrahigh peak responsivity greater than 93 A W⁻¹ and a detectivity of 2.5 × 10¹⁵ Jones, together with excellent reproducibility and stability. The maximum responsivities can be modulated by piezo–phototronic effect with an effective enhancement ratio of 480%. This work will open up a new route of designing MHP ferroelectric films for high‐performance PDs and offers the opportunity to utilize it for various optoelectronics applications.