Efficient CH₃NH₃PbI₃ perovskite solar cells with 2TPA-n-DP hole-transporting layers

CH₃NH₃PbI₃ perovskite solar cells with 2TPA-n-DP (TPA = 4, 4′-((1E, 1′E, 3E, 3′E)-[1, 1′-biphenyl]-4, 4′-diylbis(buta-1, 3-diene-4, 1-diyl)); DP = bis(N, N-di-p-tolylaniline); n = 1, 2, 3, 4) as hole-transporting materials (HTMs) have been fabricated. After optimization of the mesoporous TiO₂ film thickness, devices based on 2TPA-2-DP with power conversion efficiencies (PCEs) of up to 12.96% have been achieved, comparable to those of devices with (2, 2′, 7, 7′-tetrakis(N, N-di-p-methoxyphenylamine)-9, 9′-spirobifluorene) (spiro-OMeTAD) as HTM under similar conditions. Further time-resolved photoluminescence (PL) measurements showed a fast charge transfer process at the perovskite/2TPA-2-DP interface. With the aid of electrochemical impedance spectra, a study of the electron blocking ability of 2TPA-2-DP in the device reveals that the presence of 2TPA-2-DP can greatly increase charge transfer resistance at the HTM/Au interface in the device, thus reducing the recombination. Furthermore, the perovskite solar cells based on these four HTMs exhibit good stability after testing for one month.