N,N-Di-para-methylthiophenylamine-Substituted (2-Ethylhexyl)-9H-Carbazole: A Simple, Dopant-Free Hole-Transporting Material for Planar Perovskite Solar Cells

A dopant-free hole-transporting material (HTM), with (2-ethylhexyl)-9H-carbazole as core and N,N-di-p-methylthiophenylamine as end groups, termed CMT, has been designed and synthesized by a simple method. For the first time, four methylthiol groups have been introduced, rather than methoxy groups, at the para position of the diphenylamine. Under AM 1.5 illumination at 100 mW cm–2, perovskite solar cells based on CH3NH3PbI3 with pristine CMT as the HTM achieved a power conversion efficiency of 13.05%, with a short-circuit current density of 21.82 mA cm–2, an open-circuit voltage (VOC) of 1.03 V, and a fill factor of 58.23%. The value of VOC is comparable to that of the device based on 2,2′,7,7′-tetrakis(N,N-di-para-methoxy-phenylamino)-9,9′-spirobifluorene, which was 1.02 V.