Two-dimensional (2D) semiconductor colloidal nanoplatelets (NPLs) have shown great potential as light-harvesting materials due to their advanced optical properties. Here, we designed hybrid nanostructures of 2D CdSe nanoplatelets with phenothiazine (PTZ) for high-performance photodetector with varying thickness of CdSe NPLs by controlling the charge transfer process. Significant photoluminescence quenching and the shortening of the average decay time of CdSe NPLs in the presence of PTZ reveal the charge transfer process. Transient absorption spectroscopic analysis reveals the hot carrier cooling dynamics varies with changing the thickness of monolayers (ML) of CdSe NPLs. Furthermore, the slow exciton recombination of CdSe NPLs in the presence of PTZ indicates the efficient charge separation. The optimized CdSe NPLs-PTZ hybrid exhibits a significant enhancement of photocurrent (∼(4.7 × 103)-fold photo-to-dark current ratio) as compared to pure 3 ML CdSe NPLs (∼10 fold) at the applied voltage of 1.5 V. The measured external quantum efficiency, maximum detectivity, and response time for the optimized hybrid are found to be ∼40%, 4 × 1011 Jones, and 107 ms, with the responsivity value of 160 mA/W. These highly efficient measured parameters clearly suggest that CdSe NPLs-PTZ hybrid systems are a promising alternate for ultrasensitive photodetector.

The understanding of ultrafast carrier relaxation process in doped semiconductor quantum dots (QDs) is very important for their potential applications in light-emitting diodes, optoelectronics. Here, we have studied the change in electronic properties of Cu-doped CdSe QDs upon light illumination. The light-induced effect leads to the enhancement of the band edge decay time and reduces the decay time of the dopant emission due to photocorrosion of Cu-doped CdSe QDs. The bleaching recovery kinetics and the hot electron cooling dynamics have been studied by using femtosecond transient absorption spectroscopy. It is observed that the electron cooling process of doped CdSe QDs is dependent on the dopant concentration and the cooling kinetics of doped CdSe QDs are found to be slower than undoped QDs. After light irradiation, the cooling processes of hot electron and recovery process in doped systems are modified.

Two-dimensional (2D) material-based composites are considered to be an important class of materials for light-harvesting applications because of their efficient charge separation. In this article, we have designed composites of 2D CdSe nanoplatelets (NPLs) and CsPbX 3 (X = mixture of Br and I or I) perovskite nanocrystals and investigated their ultrafast carrier dynamics using ultrafast spectroscopy. A time-resolved fluorescence upconversion study reveals that the electron transfer from CdSe NPLs to CsPbX 3 varies with changing the composition of perovskite from CsPbBr 1.5 I 1.5 to CsPbI 3 . From the transient absorption spectroscopic study, the shortening of the faster component of bleach recovery kinetics of CdSe NPLs along with the enhancement of growth time of CsPbX 3 NCs in composites indicates the ultrafast electron transfer from CdSe NPLs to CsPbX 3 NCs. The ultrafast electron transfer from 2D CdSe NPLs to CsPbX 3 NCs enhances in the following order: CsPbI 3 > CsPbBrI 2 > CsPbBr 1.5 I 1.5 . The dark current and photocurrent are 0.04 and 62.4 μA in the CdSe−CsPbI 3 composite. The dramatically improved photocurrent response in the CdSe−CsPbI 3 composite confirms the enhancement of their efficient charge separation because of the ultrafast electron transfer from CdSe NPLs to pervoskite NCs. Our finding reveals that the integration of 2D CdSe NPLs with perovskite NCs offers a great opportunity for the improvement of the efficiency of perovskite solar cells by engineering the interfacial chargetransfer dynamics.

The electronic interactions between colloidal two-dimensional (2D) semiconductor nanoplatelets (NPLs) and Au nanoclusters (NCs) remain unexplored, which are decisive for optoelectronic applications. Here, we report the synthesis of heterostructures based on colloidal 2D CdSe NPLs and Au 25 NCs and investigate their electronic interactions using density functional theory (DFT) calculations. The steady state, time-resolved photoluminescence, and transient absorption (TA) spectroscopic studies are carried out to understand the charge-transfer dynamics. The replacement of CdSe bands by Au bands in the valence band edge in CdSe NPLs−Au NCs heterostructures attests the charge transfer from the conduction band of CdSe to Au. Ultrafast TA spectroscopy further confirms the electron transfer in the heterostructures, and the faster bleach recovery kinetics is also observed in CdSe NPLs−Au NCs heterostructures. The observed charge transfer from the conduction band of CdSe NPLs to Au NCs has been corroborated by the difference in the orbital composition of the valence band edges between CdSe and Au NCs, as calculated by DFT. Photodetectors fabricated with these heterostructures feature high enhancement in photocurrent (∼350-fold), fast photoresponse (∼200 ms), and high detectivity (∼2.5 × 10 11 Jones), which hold promise for the future design of 2D NPL-based materials for optoelectronic applications.

The strategy of a new generation of light-harvesting systems based on two-dimensional (2D) colloidal semiconductor nanoplatelets (NPLs) is an emerging field of research owing to the strong confinement in one direction, narrow emission, large exciton binding energy, and large absorption cross-section. In this Perspective, we provide fundamental insights into the ultrafast dynamics and luminescent properties of 2D semiconductor NPLs and their heterostructures. The variation of hot carrier cooling dynamics with changing the thickness of monolayers of CdSe NPLs is evident. Slow exciton recombination of 2D NPLs is reported in the presence of electron and hole acceptor molecules, indicating efficient charge separation which eventually controls the device performance. We envision the possibility of designing 2D NPLs heterostructures in combination with metal clusters, perovskite nanocrystals, and graphene oxide for photodetector, light-emitting diodes, photocatalysis, electroluminescence, and photovoltaics applications by controlling their charge transfer dynamics. The future perspective of this research field with promising areas is discussed.