Fig. 1. Inverted perovskite solar cell. (a) Device structure; (b) crystal structure of perovskite^[43]

Fig. 2. BCP devices were fabricated at different spin coating speeds. (a) Energy level matching diagram; (b) current density-voltage (J-V) curves^[75]

Fig. 3. Interface performance of PCBM modified by different metal oxides. (a) J-V curves and (b) thermal stability measurement of Nb-TiO₂^[79]; (c) J-V curves and (d) thermal stability measurement of TBAOH-SnO₂^[31]

Fig. 4. Structure diagram and J-V curves of different materials. (a) Molecular structure diagram of Triton X-100; (b) J-V curves of s-PCBM with different mass fractions^[68]; (c) synthesis of C₆₀-tBu-I; (d) structural principle and J-V curves^[27]

Fig. 5. Correlation Diagram of ETL improvement by different polymers. (a) Molecular structure diagram of PS^[32],PFNOX^[63], and PNDI-2T^[86]; (b) device ETL is the photoelectric voltage attenuation curves of PCBM: PS^[32]; (c) J-V curves of PNDI-2T with different doping ratios; (d) stable photocurrent density and PCE of doped and undoped PNDI-2T PSCs at maximum power point^[86]

Fig. 6. Different carbon materials doped with PCBM. (a) J-V curves (inset: external quantum efficiency spectrum of optimal PCBM); (b) luminescence spectrum ^[33]; (c) J-V curves of ETL with different proportions of C₆₀; (d) schematic of free carrier generation rate and electron transfer mechanism from perovskite layer to different ETLs of original PC₆₁BM and PC₆₁BM∶C₆₀(1∶0.07) ^[82]

Fig. 7. PCBM doped with different materials. (a) Molecular structure diagram of IZ、BIZ^[76]; (b) passivation of surface traps in perovskite films and Doped PC₆₁BM electron transport layer^[69];(c) J-V curves of Doped iz or biz^[76]; (d) J-V curves (PSC Ref represents original PC₇₀BM, PSC-Dop2 represents 2% Bi₂Te₃ in doped PC₇₀BM, PSC-Int2 represents 2 SC Bi₂Te₃ with intermediate layer, and PSC-Com2 represents both doped and intermediate layer); (e) long term ISOS-L2 stability measurement^[34]

Fig. 8. [in Chinese]

Fig. 9. Performance of different polymers doped with ETL. (a) Mechanical stability diagram before and after doping P(NDI2DT-TTCN) ^[95]; (b) electronic conductivity of doped TPA-3CN; (c) PL spectra; (d) J-V curves of flexible devices^[96]

Fig. 10. Correlation diagram of different organic small molecules in ETL. (a) Molecular structure diagram of DS1、DS2^[92]、IT-4F、IT-4H、IT-4M^[98]、TTIC-4F^[85]; (b) research on the correlation between V_OC and LUMO based on IT-4F, IT-4H and IT-4M; (c) device stability measurement of unpackaged PSCs containing ETL in ambient atmosphere^[98]

Fig. 11. Relevant performance of different materials as ETL.(a) Molecular structure diagram of Q10; (b) ETL is the J-V curves of conductivity of Q10; (c) TRPL spectrum with ETL of Q10^[99]; (d) C²-V of PSCs based on different ETL; (e) steady state spectra of perovskite coated on glass,In₂O₃,Sn∶In₂O₃, and Sn∶In₂O₃/In₂O₃ bilayers^[100]

Table 1. Performance of inverted perovskite solar cells with fullerene as electron transport layer

Table 2. Performance of inverted perovskite solar cells with non-fullerene electron transport layer

Table 3. Photoelectric parameters of inverted perovskite solar cells with Alq3 and C60 of different thicknesses^{［52，77］}