Observation of the slower thermalization process with increasing IA in CsPbIxBr3−x perovskite quantum dots for wider bandgap solar cell absorber

Conventional single junction solar cells are fundamentally limited by the Shockley–Queisser efficiency limit, while hot carrier solar cell (HCSC) aims to overcome this through efficient hot carrier extraction, thereby revitalizing the application prospects of wide bandgap materials in photovoltaic technologies. This study demonstrates that isonicotinamide (IA)—previously shown to enhance bulk perovskite solar cells via defect passivation—can be strategically applied to quantum dots (QDs) by replacing oleylamine (OLA) ligands. Systematic studies reveal a non-monotonic dependence of the thermalization coefficient (Qth) on IA/OLA ratios in CsPbIxBr3−x QDs. At optimal concentrations, Qth decreases to 1.89 ± 0.059 mW⋅K−1⋅cm−2, accompanied by a prolonged carrier lifetime (17.7 ns), attributed to dual functional groups of IA passivating undercoordinated Pb defects. However, excess IA overcrowds surfaces of QDs, displacing OLA and creating new defects that increase Qth. These competing effects determine an optimal IA/OLA ratio for Qth minimization, which is almost two orders of magnitude lower than in bulk materials. The suppressed hot carrier thermalization could significantly enhance the maximum achievable power conversion efficiency of HCSC. This work establishes the perovskite QDs as promising wide bandgap absorbers for HCSC and provides a ligand-engineering strategy to optimize hot carrier dynamics.