2D hybrid halide double perovskites (HHDPs) have been demonstrated to be a promising alternative to conventional lead-based halide perovskites as a new system of photoferroelectrics, due to their unique characteristics of environmental friendliness, favorable stability, and fascinating optoelectronic properties. Herein, for the first time, a 2D iodide double perovskite photoferroelectric is reported based on Ag/Sb ions, (4,4-DFPD) 4 AgSbI 8 (4,4-DFPD = 4,4-difluoropiperidinium), which possesses a high Curie temperature of 414 K (above BaTiO 3 ), a large spontaneous polarization of 9.6 µC cm −2 , ferroelectric photovoltaic effect, and photostrictive effect. Notably, to the best of the authors' knowledge, the discovery of photostriction in HHDP photoferroelectrics is unprecedented. Moreover, (4,4-DFPD) 4 AgSbI 8 exhibits an impressive X-ray responsivity, with a sensitivity as high as 704.8 µC Gy air −1 cm −2 at 100 V bias and a detection limit as low as 0.36 µGy air s −1 at 10 V bias, both of which outperform the current all HHDP photoferroelectrics. This work enriches the photoferroelectric family, and proves that Ag/Sb-based HHDP photoferroelectrics are a promising candidate for the next-generation optoelectronic devices.

Tin organic-inorganic halide perovskites (tin OIHPs) possess a desirable band gap and their power conversion efficiency (PCE) has reached 14 %. A commonly held view is that the organic cations in tin OIHPs would have little impact on the optoelectronic properties. Herein, we show that the defective organic cations with randomly dynamic characteristics can have marked effect on optoelectronic properties of the tin OIHPs. Hydrogen vacancies originated from the proton dissociation from FA [HC(NH 2 ) 2 ] in FASnI 3 can induce deep transition levels in the band gap but yield relatively small nonradiative recombination coefficients of 10 À 15 cm 3 s À 1 , whereas those from MA (CH 3 NH 3 ) in MASnI 3 can yield much larger nonradiative recombination coefficients of 10 À 11 cm 3 s À 1 . Additional insight into the "defect tolerance" is gained by disentangling the correlations between dynamic rotation of organic cations and charge-carrier dynamics.

The development of perovskite light-emitting diodes (PeLEDs) has progressed rapidly over the past several years, with high external quantum efficiencies exceeding 20%. However, the deployment of PeLEDs in commercial devices...

Tin organic-inorganic halide perovskites (tin OIHPs) possess a desirable band gap and their power conversion efficiency (PCE) has reached 14 %. A commonly held view is that the organic cations in tin OIHPs would have little impact on the optoelectronic properties. Herein, we show that the defective organic cations with randomly dynamic characteristics can have marked effect on optoelectronic properties of the tin OIHPs. Hydrogen vacancies originated from the proton dissociation from FA [HC(NH 2 ) 2 ] in FASnI 3 can induce deep transition levels in the band gap but yield relatively small nonradiative recombination coefficients of 10 À 15 cm 3 s À 1 , whereas those from MA (CH 3 NH 3 ) in MASnI 3 can yield much larger nonradiative recombination coefficients of 10 À 11 cm 3 s À 1 . Additional insight into the "defect tolerance" is gained by disentangling the correlations between dynamic rotation of organic cations and charge-carrier dynamics.