Engineering charge transfer pathways in anion exchanged CsPbBr_3-xCl_x perovskite nanocrystals with fullerene

The optoelectronic efficacies of lead halide perovskite nanocrystal (PNC)-driven devices are often assessed by the interfacial charge-transfer (CT) dynamics between the active layer and the adjacent charge-transporting layers. Enhanced device performance typically requires efficient charge-carrier generation, swift CT dynamics, effective carrier extraction, and reduced recombination losses. In the current study, we have attempted to unveil the underlying photoinduced CT kinetics among the compositionally tuned CsPb(Br/Cl)₃ PNCs with fullerene (C₆₀) through a series of steady-state and time-resolved spectroscopic and conductivity measurements along with simulations. Among the investigated systems, the mixed-halide CsPb(Br/Cl)₃ PNCs exhibit a markedly higher CT rate with C₆₀ compared to their pristine CsPbBr₃ and CsPbCl₃ counterparts. The analysis further uncovers signatures of both electron and hole transfer processes at the CsPb(Br/Cl)₃-C₆₀ interface, indicating a more efficient dual-channel deactivation pathway. Conductive atomic force microscopy shows enhanced conductivity and the most significant relative resistance reduction for CsPb(Br/Cl)₃-C₆₀, evidencing superior charge injection and transport. Complementarily, a one-dimensional solar cell capacitance simulator (SCAPS-1D) further reveals that incorporation of C₆₀ enhances the photovoltaic parameters, with the CsPb(Br/Cl)₃-based device showing the most pronounced improvement, in agreement with the spectroscopic and conductance measurements. These results provide crucial insights into strategies for tailoring PNC-based optoelectronic devices towards higher efficiency while highlighting the critical influence of CT in governing charge transport and device performance.