Fig. 1. (Color online) The PCE evolution of FPSCs from 2013 to 2021^[17–26].

Fig. 2. (Color online) High-efficiency FPSC based on PEN and PET substrates. (a) Schematic diagram of the FPSC structure based on a perovskite layer doped with artemisinin. (b) J–V curves on rigid and flexible substrates with and without artemisinin doping^[17]. (c) Scanning electron microscope characterization of thin film deposited on glass/fluorine-doped tin oxide (FTO) substrate^[26]. (d) The room temperature sheet resistance of conductive PET/ITO, PEN/ITO, glass/ITO, and glass/FTO substrates after heat treatment at different temperatures for 30 min^[29].

Fig. 3. (Color online) (a) Schematic diagram of FPSC structure based on Ti foil. (b) J–V curves of Au/Cu/HTM/CH₃NH₃PbI₃/TiO₂/Ti cells under 100 mW/cm² AM 1.5G solar light with the same oxidized thickness of TiO₂ layer (~50 nm) based on the same ambience, air, with different annealing temperatures^[35]. (c) FPSC cross-section SEM based on ultra-thin Willow Glass substrate^[37]. (d) Static contact angle of deionized water on PDMS layers with different aspect ratios. (e) Photograph of a flexible perovskite module. (f) J–V curve of the champion flexible perovskite modules^[38].

Fig. 4. (Color online) (a) Flexible perovskite device diagram^[18]. (b) J–V curve of FPSC based on ZnO prepared at low temperature. (c) Light and dark J–V curves of FPSC^[41]. (d) J–V curve under different ALD cycles. (e) Optimized FPSC structure and its J–V curve. (f) Variation of VOC, JSC, FF and PCE with bending times^[42].

Fig. 5. (Color online) (a) The first FPSC based on the TiO₂ electron transport layer and (b) its J–V curve as the FPSCs performance of the electron transport layer^[49]. (c) Steady-state PL spectra of glass/perovskite, FTO/anatase-TiO₂/perovskite and FTO/amorphous-TiO₂/perovskite film^[50]. (d) FPSC cross-section scanning electron microscope with ALD deposited TiO₂ dense layer and UV-irradiated mesoporous TiO₂^[51]. (e) Impedance diagram (Z"– Z')^[57].

Fig. 6. (Color online) (a) Schematic diagram of the fabrication of nanostructured NiO_x thin films^[65]. (b) Cu-doped NiO_x FPSC device structure^[67]. (c) PhNa-1T structure diagram (d) Energy band diagram using different hole transport layers^[68].

Fig. 7. (Color online) (a) Schematic diagram of the device prepared by blade coating method^[73]. (b) Blow N₂ gas and precursor solution with the addition of NH₄Cl^[38]. (c) J–V curve under an area of 8 mm². (d) J–V curve under an area of 42.9 cm². (e) Double hole transport Energy band diagram. (f, g) Under the layer MAPbI₃, PTAA/MAPbI₃ and PEDOT:PSS/MAPbI₃ diagram of PL and its partial enlargement^[74].

Fig. 8. (Color online) (a) Resistance change of multilayer structure with bending cycle (ΔR/R₀ (%)). (b, c) Low-magnification SEM images of PEN/ITO/TiO_x/perovskite and PEN/TiO_x/perovskite after 300 bending cycles, scale bar: 100 μm^[86]. (d) The bionic mechanism of vertebrae and FPSCs. (e) PCE of FPSC after 500 cycles of bending at different bending radii. (f) The average PCE value of FPSC with a bending radius of 3 mm and bending 7000 cycles^[25].

Table 1. Performance parameters of polymer substrate^[28].