Boosting PhotovoltaicEfficiency: The Role of LongitudinalCarrier Transport in Carbon Dot-Modified Perovskite Films

Defect passivation engineering, an effective strategy to optimize grain boundaries and reduce defects in organic–inorganic hybrid perovskites, has been widely used to improve device performance; however, knowledge of its impact on the carrier transport property is still limited. Herein, we take carbon dot (CD) passivation as an example to explore the effect of surface modification on the longitudinal carrier diffusivity (D) in CH₃NH₃PbI₃ perovskite films by using transient reflection spectroscopy. The results show that the D value remarkably increases from 0.30 cm² s^–1 in unmodified film to 1.02 cm² s^–1 in CD-modified film due to their enhanced conductivity, where CDs act as a highly conductive interstitial medium to enhance intergrain contact. Benefiting from the increase in carrier diffusivity, the power conversion efficiency of CD-modified perovskite solar cells (PSCs) increased from 23.1% (unmodified) to 25.4%, strongly confirming the positive effect of CD passivation on the PSC performance. Our finding highlights a novel avenue for enhancing PSC performance through the improvement of longitudinal carrier diffusivity via high-conductivity nanomaterial doping.