Fig. 1. Crystal structure of perovskites. (a) Crystal structure of ABX3 perovskites. (b) Tolerance factors (t) of a series of halide perovskites. (c) Schematic diagram of the temperature-induced phase transition of FASnI3. Reproduced with permission from Ref. 33. (d) XRD patterns of MASnI3 during two sequential compression−decompression cycles. Reproduced with permission from Ref. 34.

Fig. 2. TiPes with different dimensions. (a) Schematic diagram illustrating the reduction in size and dimensionality of TiPes. (b) Typical examples of ammonium cations used to reduce the dimensionality of TiPes.

Fig. 3. Charge carrier and exciton properties. Schematic diagram of (a) carrier generation (including hot carrier generation) and (b) carrier recombination. (c)–(e) Energy-dependent and time-dependent photoluminescence spectra of perovskite thin films at low and high excitation densities for FASnI3, FAPbI3, and MAPbI3, showing that the FASnI3 thin films exhibit a much stronger band-filling effect and prolonged hot carrier emission. Reproduced with permission from Ref. 21. (f) Dark conductivity spectra (real part). (g) OPTPS measurements of the charge-carrier recombination dynamics of FASnI3 thin films treated with SnF2. Reproduced with permission from Ref. 71.

Fig. 4. Band structure and optical properties. (a) Energy band of MASnI3 and MAPbI3. Reproduced with permission from Ref. 91. Based on SOC-GW calculation: (b) electronic DOS of MASnI3 and (c) energy band structure of MASnI3 and MAPbI3. Reproduced with permission from Ref. 92. (d) Schematic energy level diagram of tin and lead perovskites. Reproduced with permission from Ref. 93. (e) Optical absorption and steady-state PL spectra of CsSnX3. Reproduced with permission from Ref. 94. (f) Optical absorption spectra and (g) PL emission spectra of TiPes [x represents the percentage of MA+ substituted by ethylenediamine ions (en)]. Reproduced with permission from Ref. 95.

Fig. 5. Environmental and operational stability. (a) Electronic structure of Sn and Pb atoms. (b) Schematic of typical TiPes device degradation. Reproduced with permission from Ref. 113. (c) Schematic diagram of vanillin reduction of TiPes. Reproduced with permission from Ref. 114. (d) Schematic diagram of 2D DJ-phase TiPes. Reproduced with permission from Ref. 115. (e) Schematic of the encapsulation of TiPes with poly(methyl methacrylate) and Al2O3. Reproduced with permission from Ref. 116.

Fig. 6. Fabrication of polycrystalline TiPes films. (a) Schematic diagram of one-step deposition method for MASnI3 film preparation. Reproduced with permission from Ref. 138. (b) Schematic diagram of MASnI3 film preparation based on ion exchange/insertion reaction. Reproduced with permission from Ref. 139.

Fig. 7. Fabrication of single crystals, nanocrystals, and quantum dots. (a) Schematic diagram of (4-FPEA)2SnI4 single crystals prepared by slow solution temperature lowering method. Reproduced with permission from Ref. 165. (b) Schematic for the synthesis of CsSnI3 nanocrystal by the hot injection. (c) TEM images of CsSnI3 nanocrystal with different Cs:Sn ratios. Reproduced with permission from Ref. 166.

Fig. 8. Application of TiPes in solar cells. (a) Schematic diagram of formal and inverted solar cell structure. Reproduced with permission from Ref. 192. (b) Schematic crystal structures of trans-2, trans-3, trans-4, and e. Reproduced with permission from Ref. 193. (c) Schematic illustration of the interface between F3-TMOS, NH2-TMOS anchored PEDOT:PSS and TiPes. (d) Current density voltage curves. (e) EQE spectra of tin PSCs with/without F3-TMOS. Reproduced with permission from Ref. 194. (f) Schematic diagram of FPEABr molecular dipole. (g) Ultraviolet photoelectron spectra (UPS) of FASnI3 films with and without FPEABr. (h) Schematic diagram of interface dipole and (i) energy level alignment. Reproduced with permission from Ref. 23.

Fig. 9. Application of TiPes in light-emitting diodes. (a) Schematic of the LED device structure. (b) Cross-sectional SEM image of LED device (scale bar: 100 nm). (c) Current density and radiance-dependent EQE of TiPes LED. Reproduced with permission from Ref. 231. (d) Crystal structure image of PEA2SnI4 perovskite and electrostatic potential image of GSH. (e) Photos of air aging (40% RH, 25°C) of PEA2SnI4 perovskite with and without GSH addition. Reproduced with permission from Ref. 232. (f) EL spectra of CsSnI3 LED with moisture treatment. (g) Statistical results and (h) operation lifetime test results of EQE with and without moisture treatment for CsSnI3 LEDs. Reproduced with permission from Ref. 222.

Fig. 10. Application of TiPes in photodetectors. (a) Schematic diagram of the effect of halogen ion migration on the barrier. Reproduced with permission from Ref. 27. (b) Schematic diagram of fabrication of CsSnI3 PDs. Reproduced with permission from Ref. 237. (c) Responsivity of the flexible FASnI3 PDs with and without CNI treatment. (d) Schematic diagram of photoplethysmography test. (e) Heart rate results of rigid (blue) and flexible (red) FASnI3 PDs with CNI treatment at 0 V and 200μWcm−2 light intensity. Reproduced with permission from Ref. 238.

Fig. 11. Application in lasing. (a) RL spectra and (b) normalized RL spectra of FASnI3 thin film at different excitation fluences (20 K, excitation by 532 nm pulses). Reproduced with permission from Ref. 244. (c) Temperature-dependent PL spectra of PEA2SnI4 at an excitation fluence of 2mJcm−2 and (d) FWHM of the ASE peak. Reproduced with permission from Ref. 245. (e) Schematic presentation of BA+ substitution by conjugated monomers. (f) Lasing spectra for (PEA)2SnI4 at 129μJcm−2, (2T)2SnI4 at 210μJcm−2, and (3T)2SnI4 at 252μJcm−2 [Inset is a lasing image of (3T)2SnI4]. (g) Temperature-dependent PL spectra of (3T)2MASn2I7 at different excitation fluences. Reproduced with permission from Ref. 25.

Fig. 12. Application of TiPes in transistors. (a) TFTs structure. (b) Transfer characteristics of TFTs with different halogen-substituted TiPes. Reproduced with permission from Ref. 26. (c) Inverter structure and optical image. (d) Butterfly voltage transfer characteristic (VDD=12.5V); noise margin (NM) in blue color. (e) Gain [=(dVout)/(dVin)]. Reproduced with permission from Ref. 249.

Fig. 13. Applications of TiPes in memory capacitor and sensor. (a) Schematic diagram of ITO/MASnBr3/Au device structure. (b) Typical C–V and Q–V loops detected at 1 MHz. Reproduced with permission from Ref. 252. (c) Sensitivity of modified PEA2SnI4 to various gases (gas concentration of 0.5%). (d) Response of the TiPes sensor to oxygen in a wet or dry atmosphere. Reproduced with permission from Ref. 253.