Phase-modulated quantum-sized TMDs for extreme saturable absorption

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-MoSe_(2),2H-WSe_(2),and Td-WTe2)remain stable during the transformation from bulk to QSs.However,phase transition(from Td 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.

Lateral quantum confinement regulates charge carrier transfer and biexciton interaction in CdSe/CdSeS core/crown nanoplatelets

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.

Sulfur vs. tellurium: the heteroatom effects on the nonfullerene acceptors

The effect of chalcogen heteroatom variation on donor materials has been systematically investigated. However, this effect on acceptors has rarely been explored. Herein, nonfullerene acceptors BFPSP and BFPTP were reported by simply changing the chalcogen atoms from S to Te. The differences between BFPSP and BFPTP in light absorption, energy levels, excited-state lifetimes, energy loss, charge mobilities, morphology, and photovoltaic properties were systematically investigated to understand the heteroatom effects. More importantly, the electroluminescence spectra, external quantum efficiency of photovoltaics and TDDFTcalculations revealed that the triplet excited state(T1) in energy of BFPTP equals to the charge transfer(CT) state in PBDBT:BFPTP, which allows T1 excitons, generated by intersystem crossing, to split into free charges to contribute to the efficiency.This contribution provides a strategy for tuning the photophysical properties of nonfullerene acceptors and designing high performance triplet materials for OSCs.

Phase/size dual controlled 2D semiconductor In_(2)X_(3)(X=S,Se,Te)for saturable absorption modulation

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 remainβ-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 In_(2)S_(3),In_(2)Se_(3),and In2Te3 quantum sheets,respectively.Our method paves the way for mass production and full exploration of full-scale 2D NSs.

Investigation of charge transfer between donor and acceptor for small-molecule organic solar cells by scanning tunneling microscopy and ultrafast transient absorption spectroscopy

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···πinteraction.With the assistance of S···πinteraction 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.