Quantized Photocatalysis Using Bandgap-Engineered Metal Halide Perovskite Nanocrystals

Size quantization in semiconductor quantum dots (QDs) offers a convenient way to tune their bandgap and energy levels of conduction and valence bands. We have now employed a room-temperature synthesis of CsPbBr3 and CsPbI3 quantum dots, with sizes from 5 to 13.5 nm, to probe hole transfer to p-phenylenediamine and m-phenylenediamine. The apparent hole-transfer rate constants, as estimated from transient absorption spectroscopy measurements, indicate a strong dependence on QD size. The shift in the valence-band energy with decreasing QD size increases the driving force (−ΔG) for hole transfer. The apparent hole-transfer rate constants, which vary in the range of (1.5 ± 0.2) – (17.3 ± 0.6) × 1010 s–1 exhibit a dependence on the energy difference between the QD valence band energy and the oxidation potential of the hole acceptor. This dependence of the rate constants further establishes the normal and inverted regions, as expected from Marcus electron-transfer theory. The ability to modulate charge-transfer rate constants through size control paves the way for tailoring the performance of quantized photocatalytic systems.