Experimental investigation of additive free-low-cost vinyl triarylamines based hole transport material for FAPbI3-based perovskite solar cells to enhance efficiency and stability

Perovskite-based solar cells have drawn a lot of attention recently because they possess many desirable qualities, including strong photon absorption, large carrier lifetime, ambipolar transmission, and low exciton binding energy. With continual optimization of each functional layer, particularly the active layer and hole transporting layer, the power conversion efficiency (PCE) of perovskite materials has reached over 25%. Spiro-OMeTAD is a widely utilized hole transport material (HTM) for efficient solar cell operation. To improve conductivity, this material is often doped with additives such as 4-tert-butylpyridine (TBP) or bis(trifluoromethane)sulfonimide lithium salt (Li-TFSI). Unfortunately, these additives can weaken the perovskite layer and reduce device stability. In this work, we enhanced the efficiency as well as stability of formamidinium-based perovskite using additive-free, cost-effective HTM based on vinyl triarylamines developed by the Tokyo chemical industry. We have deposited vinyl triarylamines-based HTM on both FAPbI3 and MAPbI3 perovskite. To compare the results, we have deposited traditional additive-based as well as additive free Spiro-OMeTAD on FAPbI3 perovskite. Results are encouraging as the FAPbI3-based device showed a decent power conversion efficiency of 16.86%, which is higher than when the same HTM is deposited on the MAPbI3-based device and comparable with doped Spiro-OMeTAD and much higher than undoped Spiro-OMeTAD based HTM deposited on FAPbI3 perovskite. Enhancement in device performance is attributed to better hole mobility and favourable energy band positioning of vinyl triarylamines based hole transport layer w.r.t FAPbI3 perovskite. The PCE of a FAPbI3-based device using the suggested HTM (SHTM) suffers only a 12% decrease while following the maximum power point for 1800 h in ambient air.