Back interface engineering by 2D layered N–Ti3C2 in low-cost carbon based all-inorganic hole transport layer free perovskite solar cells

The mismatched energy level alignments, back interface defects in the perovskite/carbon back interface, as well as low conductivity of carbon counter electrode are the primary factors for the low photovoltaic behavior of all-inorganic hole transport layer (HTL)-free perovskite solar cells (C–PSCs) using carbon counter electrode-based. Herein, 2D layered Ti 3 C 2 and N–Ti 3 C 2 are proposed to form Ti 3 C 2 @carbon and N–Ti 3 C 2 @carbon counter electrodes for modifying the perovskite/carbon back interface. First, the appropriate work function of Ti 3 C 2 can optimize the energy level alignments. Second, nitrogen doping can enhance the conductivity of Ti 3 C 2 which can lower the total resistance of the device. Third, the specific 2D layered structure Ti 3 C 2 and N–Ti 3 C 2 can reduce back interface defects. Therefore, the perovskite/carbon back interface shows improved charge extraction and transport capabilities disclosed by photoluminescence measurements. Consequently, the power conversion efficiencies (PCE) of the C–PSCs are enhanced to 7.56 % from 5.94 % by using Ti 3 C 2 @carbon counter electrode, and further to 8.91 % by using N–Ti 3 C 2 @carbon counter electrode, indicating remarkable PCE improvements of 27.3 % and 50.0 %. Moreover, the Ti 3 C 2 @carbon and N–Ti 3 C 2 @carbon-based C–PSCs show remarkable stabilities under ambient conditions for 30 days. This work is expected to provide a feasible path to optimize the back interface of the all-inorganic C–PSCs.