Interface optimization and defects suppression via Na F introduction enable efficient flexible Sb_(2)Se_(3) thin-film solar cells

Sb_(2)Se_(3) with unique one-dimensional(1D) crystal structure exhibits exceptional deformation tolerance,demonstrating great application potential in flexible devices.However,the power conversion efficiency(PCE) of flexible Sb_(2)Se_(3) photovoltaic devices is temporarily limited by the complicated intrinsic defects and the undesirable contact interfaces.Herein,a high-quality Sb_(2)Se_(3) absorber layer with large crystal grains and benign [hkl] growth orientation can be first prepared on a Mo foil substrate.Then NaF intermediate layer is introduced between Mo and Sb_(2)Se_(3),which can further optimize the growth of Sb_(2)Se_(3)thin film.Moreover,positive Na ion diffusion enables it to dramatically lower barrier height at the back contact interface and passivate harmful defects at both bulk and heterojunction.As a result,the champion substrate structured Mo-foil/Mo/NaF/Sb_(2)Se_(3)/CdS/ITO/Ag flexible thin-film solar cell delivers an obviously higher efficiency of 8.03% and a record open-circuit voltage(V_(OC)) of 0.492 V.This flexible Sb_(2)Se_(3) device also exhibits excellent stability and flexibility to stand large bending radius and multiple bending times,as well as superior weak light photo-response with derived efficiency of 12.60%.This work presents an effective strategy to enhance the flexible Sb_(2)Se_(3) device performance and expand its potential photovoltaic applications.

Recent progress and perspectives on Sb_(2)Se_(3)-based photocathodes for solar hydrogen production via photoelectrochemical water splitting

Photoelectrochemical(PEC) cells involved with semiconductor electrodes can simultaneously absorb solar energy and perform chemical reactions, which are considered as an attractive strategy to produce renewable and clean hydrogen energy. Sb_(2)Se_(3) has been widely investigated in constructing PEC photocathodes benefitting of its low toxicity, suitable band gap, superior optoelectronic properties, and outstanding photocorrosion stability. We first present a brief overview of basic concepts and principles of PEC water splitting as well as a comparison between Sb_(2)Se_(3) and other numerous candidates. Then the material characteristics and preparation methods of Sb_(2)Se_(3) are introduced. The development of Sb_(2)Se_(3)-based photocathodes in PEC water splitting with various architectures and engineering efforts(i.e., absorber engineering, interfaces engineering, co-catalyst engineering and tandem engineering) to improve solar-to-hydrogen(STH) efficiency are highlighted. Finally, we debate the possible future directions to further explore the researching fields of Sb_(2)Se_(3)-based photocathodes with a strongly positive outlook in PEC processed solar hydrogen production.

Over 12%efficient kesterite solar cell via back interface engineering

Kesterite Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)has attracted considerable attention as a non-toxic and earthabundant solar cell material.During selenization of CZTSSe film at high temperature,the reaction between CZTSSe and Mo is one of the main reasons that result in unfavorable absorber and interface quality,which leads to large open circuit voltage deficit(VOC-def)and low fill factor(FF).Herein,a WO_(3)intermediate layer introduced at the back interface can effectually inhibit the unfavorable interface reaction between absorber and back electrode in the preliminary selenization progress;thus high-quality crystals are obtained.Through this back interface engineering,the traditional problems of phase segregation,voids in the absorber and over thick Mo(S,Se)_(2)at the back interface can be well solved,which greatly lessens the recombination in the bulk and at the interface.The increased minority carrier diffusion length,decreased barrier height at back interface contact and reduced deep acceptor defects give rise to systematic improvement in VOCand FF,finally a 12.66%conversion efficiency for CZTSSe solar cell has been achieved.This work provides a simple way to fabricate highly efficient solar cells and promotes a deeper understanding of the function of intermediate layer at back interface in kesterite-based solar cells.

High-efficiency ultra-thin Cu_(2)ZnSnS_(4) solar cells by double-pressure sputtering with spark plasma sintered quaternary target

In recent years,Cu_(2)ZnSnS_(4)(CZTS)semiconductor materials have received intensive attention in the field of thin-film solar cells owing to its non-toxic and low-cost elements.In this work,double-pressure sputtering technology is applied to obtain highly efficient and ultra-thin(-450 nm)pure Cu_(2)ZnSnS_(4)(CZTS)solar cell.Using mixed materials with sulfides and copper powder as a quaternary target via spark plasma sintering(SPS)method and adopting double-layer sputtering(high+low pressure),a highly adhesive and large-grained CZTS thin film is achieved.As a result,the damage to the surface of Mo contact is decreased so that the reflectivity of incident light can be improved.Moreover,the composition of CZTS film was more uniform and the secondary phase separation at the Mo interface was reduced.Therefore,the interface defect state and deep level defect density in corresponding device with double-pressure is reduced and the ratio of depletion thickness to absorption layer thickness can reached to 0.58,which promoted the collection of photogenerated carriers.Finally,an efficiency of 9.3%for ultra-thin(~450 nm)CZTS film solar cell is obtained.

Microstructure and 355 nm Laser-Induced Damage Characteristics of Al₂O₃Films Irradiated with Oxygen Plasma under Different Energy

Al2O3 films were prepared using electron beam evaporation at room temperature. The samples were irradiated with oxygen plasma under different energy. The variations in average surface defect density and root mean square (RMS) surface roughness were characterized using an optical microscope and an atomic force microscope. Surface average defect density increased after plasma treatment. The RMS surface roughness of the samples decreased from 1.92 nm to 1.26 nm because of surface atom restructuring after oxygen plasma conditioning. A 355 nm laser-induced damage experiment indicated that the as-grown sample with the lowest defect density exhibited a higher laser-induced damage threshold (1.12 J/cm2) than the other treated samples. Laser-induced damage images revealed that defect is one of the key factors that affect laser-induced damage on Al2O3 films.

Back contact interfacial modification mechanism in highly-efficient antimony selenide thin-film solar cells

Antimony selenide(Sb_(2)Se_(3))is a potential photovoltaic(PV)material for next-generation solar cells and has achieved great development in the last several years.The properties of Sb_(2)Se_(3)absorber and back contact influence the PV performances of Sb_(2)Se_(3)solar cells.Hence,optimization of back contact characteristics and absorber orientation are crucial steps in raising the power conversion efficiency(PCE)of Sb_(2)Se_(3)solar cells.In this work,MoO2was introduced as an intermediate layer(IL)in Sb_(2)Se_(3)solar cells,and comparative investigations were conducted.The growth of(211)-oriented Sb_(2)Se_(3)with large grains was facilitated by introducing the MoO2IL with suitable thickness.The MoO2IL substantially lowered the back contact barrier and prevented the formation of voids at the back contact,which reduced the thickness of the MoSe2interface layer,inhibited carrier recombination,and minimized bulk and interfacial defects in devices.Subsequently,significant optimization enhanced the open-circuit voltage(VOC)of solar cells from 0.481 V to 0.487 V,short-circuit current density(JSC)from 23.81 m A/cm^(2)to 29.29 m A/cm^(2),and fill factor from 50.28%to 57.10%,which boosted the PCE from 5.75%to 8.14%.

Thermodynamically induced crystal restructuring to make CsPbCl_(3) single crystal films for weak light detection

CsPbCl_(3) perovskite is considered a highly promising material for ultraviolet (UV) photodetectors due to its exceptional thermal stability and excellent short-wavelength light response. However, its high lattice energy and low polarizability result in extremely low solubility in conventional solvents, making the synthesis of CsPbCl_(3) single crystals a significant challenge. In this study, we propose a novel thermodynamically induced crystal restructuring (TICR) process that can transform microcrystalline films (MCFs) into single crystal films (SCFs) within a short period. This method, for the first time, has successfully achieved the synthesis of centimeter-sized CsPbCl_(3) SCFs and the mechanism has been explored in depth using in-situ techniques. Furthermore, we report the first instance of a CsPbCl_(3) SCF UV photodiode, which exhibits a record-breaking on/off ratio of 3.32 × 10^(7) and a detectivity of up to 1.15 × 10^(14) Jones under 0 V bias. It demonstrates excellent response even under weak light conditions of 10 nW·cm^(−2) and maintains outstanding stability with almost no performance degradation after 15 months. This study provides a novel approach for the synthesis of perovskite single crystals and holds significant potential for advancing the development of high-performance optoelectronic devices.

Potassium doping for grain boundary passivation and defect suppression enables highly-efficient kesterite solar cells

The complicated and diverse deep defects,voids,and grain boundary in the CZTSSe absorber are the main reasons for carrier recombination and efficiency degradation.The further improvement of the open-circuit voltage and fill factor so as to increase the efficiency of CZTSSe device is urgent.In this work,we obtained K-doped CZTSSe absorber by a simple solution method.The medium-sized K atoms,which combine the advantages of light and heavy alkali metals,are able to enter the grain interior as well as segregate at grain boundary.The K-Se liquid phase can improve the absorber crystallinity.We find that the accumulation of the wide bandgap compound K_(2)Sn_(2)S_(5)at grain boundary can increase the contact potential difference of grain boundary,form more effective hole barriers,and enhance the charge separation ability.At the same time,K doping passivates the interface as well as bulk defects and suppresses the non-radiative recombination.The improved crystallinity,enhanced charge transport capability and reduced defect density due to K doping result in a significant enhancement of the carrier lifetime,leading to 13.04%device efficiency.This study provides a new idea for simultaneous realization of grain boundary passivation and defect suppression in inorganic kesterite solar cells.

Carrier recombination suppression and transport enhancement enable high-performance self-powered broadband Sb_(2)Se_(3) photodetectors

Antimony selenide(Sb_(2)Se_(3))is a promising candidate for photodetector applications boasting unique material benefits and remarkable optoelectronic properties.Achieving high-performance self-powered Sb_(2)Se_(3)photodetector through a synergistic regulation of absorber layer and heterojunction interface demonstrates great potential and needs essential investigation.In this study,an effective two-step thermodynamic/kinetic deposition technique containing sputtered and selenized Sb precursor is implemented to induce self-assembled growth of Sb_(2)Se_(3)light absorbing thin film with large crystal grains and desirable[hk1]orientation,presenting considerable thin-film photodetector performance.Furthermore,aluminum(Al^(3+))cation dopant is introduced to modify the optoelectronic properties of CdS buffer layer,and further optimize the Sb_(2)Se_(3)/CdS(Al)heterojunction interface quality.Thanks to the suppressed carrier recombination and enhanced carrier transport kinetics,the champion Mo/Sb_(2)Se_(3)/CdS(Al)/ITO/Ag photodetector exhibits self-powered and broadband characteristics,accompanied by simultaneously high responsivity of 0.9 A W^(-1)(at 11 nW cm^(-2)),linear dynamic range of 120 dB,impressive ON/OFF switching ratio over 10^(6)and signal-to-noise ratio of 10^(9),record total noise determined realistic detectivity of 4.78×10^(12)Jones,and ultra-fast response speed with rise/decay time of 24/75 ns,representing the top level for Sb_(2)Se_(3)-based photodetectors.This intriguing work opens up an avenue for its selfpowered broadband photodetector applications.

Anode interfacial modification for non-fullerene polymer solar cells:Recent advances and prospects

Recently,the power conversion efficiency(PCE)of single-junction non-fullerene polymer solar cells(NF-PSCs)has surpassed 19%due to the fast development of novel donor polymers,NF-acceptors,device engineering,and interlayer materials.The anode interlayer(AIL)plays a vital role in improving the efficiency and stability of PSCs.The challenges and opportunities in this research area encourage researchers to pursue great innovation in developing new materials and strategies for highly efficient NF-PSCs.This review summarizes the recent development of AIL materials and their modification strategies in single-junction NF-PSCs.Firstly,a brief introduction,key functions,basic requirements,and peculiar features of AILs when employed in NF-PSCs are discussed.Then,the impact of AIL materials(including organic,inorganic,and hybrid materials)on the PCE and the stability of NF-PSCs are described.Afterward,the fabrication of large-area devices and related issues are highlighted.The summary and the future challenges regarding efficient AIL are summarized in the last section of this review.

Ion doping simultaneously increased the carrier density and modified the conduction type of Sb_(2)Se_(3) thin films towards quasi-homojunction solar cell

Antimony selenide(Sb_(2)Se_(3))has drawn tremendous research attentions in recent years as an environment-friendly and cost-efficient photovoltaic material.However,the intrinsic low carrier density and electrical conductivity limited its scope of applications.In this work,an effective ion doping strategy was implemented to improve the electrical and photoelectrical performances of Sb_(2)Se_(3) thin films.The Sn-doped and I-doped Sb_(2)Se_(3) thin films with controllable chemical composition can be prepared by magnetron sputtering combined with post-selenization treatment based on homemade plasma sintered targets.As a result,the Sn-doped Sb_(2)Se_(3) thin film exhibited a great increase in carrier density by several orders of magnitude,by contrast,a less increase with one order of magnitude was achieved for the Idoped Sb_(2)Se_(3) thin film.Additionally,such cation or anion doping could simultaneously modify the conduction type of Sb_(2)Se_(3),enabling the first fabrication of a substrate structured Sb_(2)Se_(3)-based quasihomojunction thin film solar cell with configuration of Mo/Sb_(2)Se_(3)-Sn/Sb_(2)Se_(3)-I/ITO/Ag.The obtained power conversion efficiency exceeding 2%undoubtedly demonstrated its attractive photovoltaic application potential and further investigation necessity.

Nonlinear optical performance of few-layer molybdenum diselenide as a slow-saturable absorber

Two-dimensional transition metal dichalcogenides are considered promising materials for next-generation photonics and nano-optical devices. Although many previous reports have shown saturable absorption of molybdenum diselenide(Mo Se2), these nonlinear optical(NLO) properties of Mo Se2 were measured in separate works and under different conditions with their hot-carrier relaxations. Here, we conducted a series of coherent studies on the NLO properties of few-layer Mo Se2 via open-aperture Z-scan and degenerate pump-probe techniques. These measurements were taken to test the materials' capabilities as a slow-saturable absorber. A slowabsorber model was employed to analyze the NLO measurements, and the results show that the NLO modulation depth was modeled to be 7.4% and 15.1% for the linear absorption coefficients of 5.22 cm-1 and 6.51 cm-1,respectively. The corresponding saturated intensities were modeled to be 39.37 MW∕cm2 and 234.75 MW∕cm2,respectively. The excitation carrier recovery time of few-layer Mo Se2 was measured by degenerate pump-probe techniques to be ～220 ps. These nonlinear optical performances make it a promising slow-saturable absorber for passive mode locking in femtosecond lasers.

The influence of sequence of precursor films on CZTSe thin films prepared by ion-beam sputtering deposition

The CuZnSn（CZT） precursor thin films are grown by ion-beam sputtering Cu, Zn, Sn targets with different orders and then sputtering Se target to fabricate Cu_2ZnSnSe_4（CZTSe） absorber thin films on molybdenum substrates. They are annealed in the same vacuum chamber at 400 ℃. The characterization methods of CZTSe thin films include X-ray diffraction（XRD）, energy dispersive spectroscopy（EDS）, scanning electron microscopy（SEM）, and X-ray photoelectron spectra（XPS） in order to study the crystallographic properties, composition, surface morphology, electrical properties and so on. The results display that the CZTSe thin films got the strongest diffraction peak intensity and were with good crystalline quality and its morphology appeared smooth and compact with a sequence of Cu/Zn/Sn/Se, which reveals that the expected states for CZTSe are Cu^（1＋）, Zn^（2＋）, Sn^（4＋）, Se^（2）.With the good crystalline quality and close to ideal stoichiometric ratio the resistivity of the CZTSe film with the sequence of Cu/Zn/Sn/Se is lower, whose optical band gap is about 1.50 eV.