Investigation of polyaniline doped with camphorsulfonic acid in chloroform solution as a hole transporting layer in PTB7: PCBM and perovskite-based solar cells

Polyaniline was chemically synthesized and protonated (doped) with CSA in chloroform with different PANI:CSA molar ratios, ranging from 6:1 to 1:4. Protonation level of the polymer was monitored by means of UV–Vis spectra of the solution and FTIR measurements of thin films. The results were correlated with the changes of specific conductivity in a function of PANI:CSA molar ratio in the films. A broad maximum of conductivity was found in the range from 1:1 to 1:3, i.e. for over-protonated polymer. The solutions with various PANI doping levels were used as hole transport layers (HTLs) in the polymer-fullerene (PTB7:PC70BM) and perovskite (MAPbI3) solar cells. The highest power conversion efficiency (PCE=3.8%) obtained for the organic cell with molar ratio PANI:CSA=1:1 was only slightly lower than that of the reference cell with PEDOT:PSS HTL (4%). The best perovskite cells achieved PCE of about 4% which was markedly lower that the efficiency of cells with Spiro-OMeTAD HTL. However, some of the perovskite cells with PANI:CSA revealed very high short current density, of about 20 mA cm−2 but relatively low open circuit photovoltage (0.42 V). The changes of the PCE in a function of PANI protonation level were discussed in terms of alignment of HOMO and LUMO levels of HTL, donor and acceptor layers in the solar cells as well as quality of interfacial layers.