Charge carrier dynamics essentially determines the performance of various optoelectronic applications of colloidal semiconductor nanocrystals. Among them, two-dimensional nanoplatelets provide new adjustment freedom for their unique core/crown heterostructures. Herein, we demonstrate that by fine-tuning the core size and the lateral quantum confinement, the charge carrier transfer rate from the crown to the core can be varied by one order of magnitude in CdSe/CdSeS core/alloy-crown nanoplatelets. In addition, the transfer can be affected by a carrier blocking mechanism, i.e., the filled carriers hinder further possible transfer. Furthermore, we found that the biexciton interaction is oppositely affected by quantum confinement and electron delocalization, resulting in a non-monotonic variation of the biexciton binding energy with the emission wavelength. This work provides new observations and insights into the charge carrier transfer dynamics and exciton interactions in colloidal nanoplatelets and will promote their further applications in lasing, display, sensing, etc.

Two-dimensional semiconductors such as transition metal dichalcogenides (TMDs) have attracted much interest in the past decade. Herein, we present an all-physical top-down method for the scalable production of the intrinsic TMD quantum sheets (QSs). The phases of the TMDs (e.g., 2H-MoSe₂, 2H-WSe₂, and T_d-WTe₂) remain stable during the transformation from bulk to QSs. However, phase transition (from T_d to 2H) is detected in MoTe₂. Such phase-modulation by size-reduction has never been reported before. The TMD QSs can be well dispersed in solvents, resulting in remarkable photoluminescence with excitation wavelength-, concentration-, and solvent-dependence. Meanwhile, the TMD QSs can be readily solution-processed into hybrid thin films, which demonstrate exceptional nonlinear saturation absorption (NSA). Notably, 2H-MoTe₂ QSs in poly(methyl methacrylate) show extremely high NSA performance with (absolute) modulation depth up to 46.6% and saturation intensity down to 0.81 MW·cm⁻². Our work paves the way towards quantum-sized TMDs.

Small-molecule organic solar cell is a category of clean energy potential device since charge transfers between donor and acceptor. The morphologies, co-assembly behavior, interaction sites, and charge transfer of BTID-nF (n = 1, 2)/PC₇₁BM donor–acceptor system in the active layer of organic solar cell have been studied employing scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), density functional theory (DFT) calculations, and transient absorption (TA) spectroscopy. The results show that BTID-1F and BTID-2F form bright strip structures, whereas BTID-nF (n = 1, 2)/PC₇₁BM form ridge-like structures with each complex composed of one BTID-nF (n = 1, 2) molecule and four PC₇₁BM molecules which adsorbed around the BTID-nF (n = 1, 2) molecule by S···π interaction. With the assistance of S···π interaction between BTID-nF (n = 1, 2) and PC₇₁BM, BTID-nF (n = 1, 2)/PC₇₁BM co-assembled ridge-like structures are more stable than the BTID-nF (n = 1, 2) ridge structures. To investigate the charge transfer of BTID-nF (n = 1, 2)/PC₇₁BM system, STS measurements, DFT calculation, and TA spectroscopy are further performed. The results show that charge transfer occurs in BTID-nF (n = 1, 2)/PC₇₁BM system with the electron transferring from BTID-nF (n = 1, 2) molecules to PC₇₁BM.

The production of two-dimensional nanosheets (2D NSs) with all sizes (1–100 nm) and few (< 10) layers is highly desired but far from satisfactory. Herein, we report an all-physical top-down method to produce indium chalcogenide (In₂X₃ (X = S, Se, Te)) NSs with wide-range (150–3.0 nm) controlled sizes. The method combines silica-assisted ball-milling and sonication-assisted solvent exfoliation to fabricate multiscale NSs with varying distributions, which are then precisely separated by cascade centrifugation. Multiple characterization techniques reveal that the as-produced In₂X₃ NSs are intrinsic and defect-free and remain β-phase during the whole process. The redispersions of In₂X₃ NSs exhibit prominent excitation wavelength-, solvent-, concentration-, and size-dependent photoluminescence. The NSs-poly(methyl methacrylate) (PMMA) hybrid thin films demonstrate strong size effects in nonlinear saturation absorption. The absolute modulation depths of 35.4%, 43.3%, 47.2% and saturation intensities of 1.63, 1.05, 0.83 MW·cm⁻² (i.e., 163, 105, and 83 nJ·cm⁻²) are derived for the In₂S₃, In₂Se₃, and In₂Te₃ quantum sheets, respectively. Our method paves the way for mass production and full exploration of full-scale 2D NSs.

Photogating and electrical gating are key physical mechanisms in organic phototransistors (OPTs). However, most OPTs are based on thick and polycrystalline films, which leads to substantially low efficiency of both photogating and electrical gating and thus reduced photoresponse. Herein, high-performance OPTs based on few-layered organic single-crystalline heterojunctions are proposed and the obstacle of thick and polycrystalline films for photodetection is overcome. Because of the molecular scale thickness of the type I organic single-crystalline heterojunctions in OPTs, both photogating and electrical gating are highly efficient. By synergy of efficient photogating and electrical gating, key figures of merit of OPTs reach the highest among those based on planar heterojunctions so far as we know. The production of few-layered organic single-crystalline heterojunctions will provide a new type of advanced materials for various applications.