Hysteresis-less inverted CH₃NH₃PbI₃ planar perovskite hybrid solar cells with 18.1% power conversion efficiency

Hysteresis-less inverted ITO/PEDOT:PSS/CH₃NH₃PbI₃ (MAPbI₃)/PCBM/Au planar hybrid solar cells with 18.1% average power conversion efficiency irrespective of the scan rate were fabricated by depositing dense pinhole-free MAPbI₃ perovskite on a PEDOT:PSS/ITO substrate via a single-step spin-coating of solubility controlled MAPbI₃ solution. The conductivities of PEDOT:PSS, PCBM, poly(triaryl amine) (PTAA):tert-butylpyrridne (tBP) + Li-bis(trifluoromethanesulfonyl)imide (Li-TFSI), MAPbI₃, and TiO₂ were 0.014, 0.016, 0.034, 0.015, and 0.00006 mS cm^-1, respectively. The average PL lifetimes (τ_av) of the inverted and normal cell were 1.277 and 1.94 ns, respectively. The diffusion coefficient (D_n) and charge carrier lifetime (τ_n) for the inverted MAPbI₃ planar hybrid solar cells were increased by 1.14-fold and 1.1-fold, respectively, compared with the conventional FTO/TiO₂/MAPbI₃/PTAA:tBP + Li-TFSI/Au planar hybrid cells. Hence, the inverted MAPbI₃ planar hybrid solar cells exhibited better power conversion efficiency and stability than the conventional MAPbI₃ cells because (i) the electron extraction from MAPbI₃ to the electron conductor was improved because the electron conductivity of PCBM is higher than that of TiO₂; (ii) the EQE value was increased by the better charge injection/separation efficiency between MAPbI₃ and PCBM, and by the higher charge collection efficiency than the conventional cell; (iii) the fill factor is improved by the increased D_n and τ_n; and (iv) the air and humidity stability is improved by the absence of corrosive additives in the device architecture and the hydrophobicity of the PCBM top layer. The reduced current density-voltage (J-V) hysteresis with respect to the scan rate and scan direction in the inverted planar hybrid solar cells could be attributed to a more balanced electron flux (J_e) and hole flux (J_h), and a reduced number of surface traps.