High-efficiency perovskite solar cells employing a conjugated donor-acceptor co-polymer as a hole-transporting materialElectronic supplementary information (ESI) available. See DOI: 10.1039/c7ra04611a

In this work, we have successfully introduced 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) as an efficient p-type dopant for donor-acceptor (D-A) co-polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4 H -cyclopenta[2,1- b ;3,4- b ′]dithiophene)- alt -4,7(2,1,3-benzothiadiazole)] (PCPDTBT) as an HTM in mesoscopic perovskite solar cells (PSCs). The bulk conductivity is significantly enhanced by 4 orders of magnitude when PCPDTBT is doped with F4TCNQ (6%, w/w). UV-vis and Fourier transform infrared spectroscopy (FTIR) results indicate the occurrence of p-doping, which results in higher bulk conductivity. The high conductivity leads to an impressive overall efficiency of 15.1%, which is considerably higher than the pristine PCPDTBT based devices (9.2%). The superior performance obtained should be largely attributed to the significant enhancement of the photocurrent density strongly correlated with a more efficient charge collection. This is the highest efficiency reported so far for PCPDTBT-based PSCs. Thus, molecularly p-doping has been demonstrated to be an effective strategy for further improving the performance of a wide range of D-A and other types of polymeric HTMs in PSCs. In this work, we have successfully demonstrated that molecularly p-doping of donor-acceptor co-polymer PCPDTBT as an efficient hole-transporting material in perovskite solar cells with a decent power conversion efficiency of 15.1%.