Slow Cooling and Transfer Dynamics of Hot Excitons in CsPbBr3 Perovskite Quantum Dots/g-CN Nanosheet Heterostructures: Implications for Optoelectronic Applications

Slowcooling and long-lived hot carrier (HC) population plays acrucial role in crossing the Shockley-Queisser limit and achievinghigh-efficiency perovskite photovoltaic devices up to 66%. Herein,we investigated the slow cooling of HCs via charge transfer in in-situsynthesized CsPbBr3 perovskite quantum dots-decorated graphiticcarbon nitride nanosheet (CsPbBr3 PQDs/g-CN NS) heterostructuresusing ultrafast transient absorption (UTA) spectroscopy. Halide perovskitesshowed excitation energy-dependent HC cooling. We examined the HCdynamics at two different excitation energies with varying excitationpump fluences. UTA revealed significantly higher slow cooling andslow bleach recovery in CsPbBr3 PQDs/g-CN NSs (i.e., 632fs and 845 ps) compared to pure CsPbBr3 PQDs (i.e., 512fs and 371 ps) at an excitation energy of 3.54 eV and a fluence of250 mu W, suggesting that HCs transfer through the heterostructureinterface. The observed slow cooling can be explained by the strongerinteraction between the organic polymeric frameworks of g-CN NSs andCsPbBr(3) PQDs, which passivates the trap states of CsPbBr3 PQDs and offers slow electron-hole recombination byslowing down the Auger recombination or the hot-phonon bottleneckeffect. Additionally, density functional theory (DFT) calculationswere carried out to shed light on band alignment at the interfaceto reveal the mechanism of efficient charge transfer in CsPbBr3 PQDs/g-CN NSs and validate the experimental findings. Theinsight of this study is quite beneficial for designing modified perovskitenanostructures for realization in perovskite solar cells in the nearfuture.