Tetrabenzotriazacorrole and its derivatives as undoped hole transporting materials for perovskite solar cells: Synthesis, device fabrication, and device performance

Phosphorous tetrabenzotriazacorrole (TBC) and its two soluble derivatives (TBC-1 and TBC-2) were synthesized and used for the first time as undoped hole transporting materials (HTMs) in MAPbI 3 perovskite solar cells (PSCs). Their performance in PSCs was measured and compared with that of Spiro-OMeTAD and phthalocyanine precursor. The fundamental properties related to HTMs are also examined. These novel HTMs are easily prepared, cost-effective, and solution processable. The materials exhibited much higher hole transport mobility and broader light absorption than pristine Spiro-OMeTAD and phthalocyanine precursor. They can work efficiently in the absence of any dopant for devices composed of FTO/cp-TiO 2 /mp-TiO 2 /MAPbI 3 /HTM/Au. The undoped mesoscopic solar cell devices based on TBC exhibited a promising power conversion efficiency (PCE) of up to 16.2% (measured at 100 mW cm 2 illumination, AM 1.5 G), together with good long-term stability under ambient conditions. This PCE of 16.2% observed using TBC is remarkably higher than the 11.2% observed using undoped Spiro-OMeTAD and also much better than the 8.70% observed using its phthalocyanine precursor. As to substitution effects, α-substituted TBC-1 was found to be a better HTM than β-substituted TBC-2 (PCE 11.4%) and unsubstituted TBC-3 (PCE 6.81%) under the same conditions. These results provide the basis for further exploiting TBC compounds as a new type of low-cost and effective HTM for PSCs.