Control of Charge Carrier Dynamics and Bandgap Renormalization in CdS Quantum Dot Hybrids by Interface Polarity

Charge carrier dynamics in wurtzite CdS quantum dots (QDs) form the basis for applications in optoelectronics and photocatalysis. We demonstrate that the quantum dynamics, energy gaps, and energy level alignments at CdS QD interfaces can be controlled by the polarity of the CdS QD surface. By performing nonadiabatic molecular dynamics simulations within a density-functional tight-binding framework, we demonstrate a strong dependence of photoinitiated processes in CdS QDs/graphene nanoribbon (GNR) hybrids on interface polarity. At room temperature, hole transfer is accelerated by a factor of 2 and exciton lifetime is enhanced by nearly an order of magnitude when the CdS QD surface is switched from polar to nonpolar. Remarkably, the interfacial bandgap for the polar QD/GNR hybrid is reduced to half upon heating from 0 K to room temperature, while it remains nearly unchanged for the nonpolar hybrid. At an intermediate temperature, the ultrafast charge separation is maintained; however, charge recombination shows the opposite trend relative to room temperature. The polar interface exhibits a longer lifetime than the nonpolar interface, due to weakened electron–phonon Fröhlich interaction and decreased gap renormalization. The strong and highly nonlinear dependence of bandgap renormalization and carrier dynamics on temperature in the polar QD/GNR hybrid is associated with significant structural reconstruction, which is absent in the nonpolar counterpart. The demonstrated control of excited-state processes by interface polarity and the strong dependence of the dynamics and energy level alignment on temperature provide key fundamental insights for informed design of modern materials for optoelectronics and energy conversion.