Fig. 1. (a)Structural diagram and energy level diagram of the perovskite solar cell based on the GO:Spiro-OMe-TAD composite HTL^[20]; (b)structural diagram of the perovskite solar cell based on the rGO:PCBM composite ETL^[22]; (c)SEM images of perovskite films on different substrates (ITO/GO, ITO/PEDOT:PSS, and bare ITO)^[29]; (d)PCE degradation trend for the perovskite solar cells with/without Ag-rGO after 330 days storage in 45%–55% relative humidity at room temperature^[38].

Fig. 2. (a)Schematic diagram of the perovskite solar cell based on the MoS₂:Spiro-OMe-TAD composite HTL ^[47]; (b)energy level diagram of the perovskite solar cell based on the MoS₂:Spiro-OMe-TAD composite HTL^[47]; (c)impedance analysis spectrum of the perovskite solar cell based on the TiO₂:MoS₂ composite ETL (R_s: the series resistance, R_sc: the shunt resistance generated by electron selective contacts, and R_rec; the shunt resistance associated with the active layer)^[52].

Fig. 3. (a)Energy level diagram of the perovskite solar cell based on the ZnO nanoparticles ETL ^[64]; (b)schematic diagram of the photodetector based on the CsPbBr₃:ZnO heterostructure ^[65]; (c)schematic diagram of the perovskite solar cell using α-CsPbI₃ quantum dots as the interface layer^[68]; (d)absorption spectra of different thin films (pristine PbS QDs, pristine CH₃NH₃PbI₃, and PbS QDs/CH₃NH₃PbI₃)^[69]; (e) SEM images of TiO₂ nanotubes before and after the perovskite deposition^[75]; (f)time-resolved photoluminescence decays of different thin films (CH₃NH₃PbI₃/NiO-NP, CH₃NH₃PbI₃/NiO-NS, and CH₃NH₃PbI₃/ZrO₂-NP)^[77].

Fig. 4. (a)Schematic diagram of the perovskite solar cell with CH₃NH₃PbI₃/Au-NRs@SiO₂ heterostructure^[83]; (b)schematic diagram and energy level diagram of the quasi-2 D perovskite solar cell incorporated with AuAg-NPs@SiO₂^[86]; (c)schematic diagram of the perovskite solar cell with a configuration of FTO/Ag-NPs@compact-TiO₂/CH₃NH₃PbI₃:TiO₂/Au^[88]; (d)steady-state PL spectra of different films (CH₃NH₃PbI₃, TiO₂/CH₃NH₃PbI₃, and TiO₂:AuAg-NPs/CH₃NH₃PbI₃)^[92].

Fig. 5. (a) Energy level diagram of the perovskite solar cell incorporated with a PS layer and schematic diagram illustrating the carrier transfer at the interface between the perovskite and HTL layers^[95]; (b) schematic diagram of the perovskite solar cell with a the PVP layer inserted between the perovskite and the HTL^[96]; (c)SEM images of the perovskite films with/without PVP ^[101]; (d) PCE degradation trend for perovskite solar cells devices with/without PVP after 30 days storage in 50% relative humidity at room temperature ^[99].