Wurtzite CZTS nanocrystals and phase evolution to kesterite thin film for solar energy harvesting

Ghorpade, Uma V.,Suryawanshi, Mahesh P.,Shin, Seung Wook,Hong, Chang Woo,Kim, Inyoung,Moon, Jong H.,Yun, Jae Ho,Kim, Jin Hyeok,Kolekar, Sanjay S. The Royal Society of Chemistry 2015 Physical chemistry chemical physics Vol.17 No.30

<P>A quaternary indium- and gallium-free kesterite (KS)-based compound, copper zinc tin sulfide (Cu<SUB>2</SUB>ZnSnS<SUB>4</SUB>, CZTS), has received significant attention for its potential applications in low cost and sustainable solar cells. It is well known that the reaction time, reactivity of the precursors, and types of capping ligands used during the synthesis of colloidal nanocrystals (NCs) strongly influence the crystallographic phase of the NCs. In this research, a non-toxic and green synthetic strategy for both the synthesis of CZTS NCs and the fabrication of a highly efficient CZTS absorber layers using an ink formulation without a toxic solvent, which meets the comprehensive framework for green chemistry that covers major aspects of the environmental strain, is demonstrated. In particular, pure metastable wurtzite (WZ) CZTS NCs are synthesized using the environmentally harmless, polyol mediated hot-injection (HI) technique at a low reaction temperature. The influence of the reaction time on the properties of the CZTS NCs is investigated in detail. Based on detailed reaction time dependent phase evolution, a possible growth and formation mechanism is proposed. Furthermore, a scalable, low cost, binder free ink formulation process without ligand exchange is developed using ethanol as the dispersal solvent. The as-prepared WZ-derived CZTS NC thin films are observed to undergo a phase transformation to KS during annealing in a sulfur vapor atmosphere <I>via</I> rapid thermal annealing above 500 °C, and surprisingly, this process results in fully sintered, compact and uniform CZTS thin films with large sized grains. The best solar cell device fabricated using a CZTS absorber that was sulfurized at an optimized temperature exhibits a power conversion efficiency of 2.44%, which is the highest efficiency obtained using the polyol-based HI route.</P> <P>Graphic Abstract</P><P>A quaternary indium- and gallium-free kesterite (KS)-based compound, copper zinc tin sulfide (Cu<SUB>2</SUB>ZnSnS<SUB>4</SUB>, CZTS), has received significant attention for its potential applications in low cost and sustainable solar cells. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5cp02007g'> </P>

Eutectic solvent-mediated selective synthesis of Cu-Sb-S-based nanocrystals: combined experimental and theoretical studies toward highly efficient water splitting

Ghorpade, Uma V.,Suryawanshi, Mahesh P.,Shin, Seung Wook,Wang, Xiaoming,Jo, Eunae,Bae, Hyojung,Park, KuSung,Ha, Jun-Seok,Kolekar, Sanjay S.,Kim, Jin Hyeok The Royal Society of Chemistry 2018 Journal of materials chemistry. A, Materials for e Vol.6 No.40

<P>Recently, emerging Cu-Sb-S-based compounds have been identified as an attractive candidate for photovoltaic (PV) applications because of their high natural abundance, eco-friendly features and typical phase-dependent characteristics. Herein, a simple eutectic solvent-mediated (choline chloride/ethylene glycol) synthetic approach for newly debuted Cu-Sb-S-based nanocrystals (NCs) with phase-selective properties is presented. This combination of material and preparation method may promote the exchange of carriers by avoiding a steric hindrance for a facile charge transport encountered in NCs prepared using amines, thiols, hydrazines and phosphine oxide solvents. A temperature-dependent study of an ethaline-based deep eutectic solvent (DES) is conducted to elucidate the characteristics of associated chemical shifts and vibrations and to determine changes in hydrogen bonding interactions using structural and thermal analytical techniques. The results suggest that ethaline is a strong candidate as a greener solvent for the synthesis of NCs at relatively low temperatures. The electronic structures of all four Cu-Sb-S phases-Cu3SbS4, CuSbS2, Cu3SbS3, and Cu12Sb4S13-were simulated using the Vienna <I>ab initio</I> Simulation (VASP) code, projector augmented-wave (PAW) potentials and the hybrid functional method (HSE 06) and using density functional theory for combined theoretical and experimental studies. Discrepancies between the experimental and theoretical bandgap values of 0.29, 0.18, 0.12 and 0.16 eV were observed for Cu3SbS4, CuSbS2, Cu3SbS3 and Cu12Sb4S13 compounds, respectively. A photoelectrochemical (PEC) water reduction system with a Mo/photoelectrode/CdS/Pt/electrolyte configuration generated a cathodic photocurrent of −1.28 and −2.72 mA cm<SUP>−2</SUP> for Cu3SbS4 and CuSbS2 electrodes, respectively, at 0 V <I>versus</I> the reversible hydrogen electrode (VRHE) under AM 1.5 G illumination, demonstrating the great potential of NCs prepared <I>via</I> eutectic solvent-mediated synthesis. This is the first successful attempt to apply eutectic solvent-mediated Cu-Sb-S NCs for solar driven H2 production. These outcomes suggest that designing proper functional materials through the application of greener synthesis strategies can improve water-splitting performance and would help meet the perpetual technological need for greener methods.</P>

SYNTHESIS OF METASTABLE WURTZITE CZTS NCs AND THEIR TRANSFORMATION INTO KESTERITE CZTS ABSORBER LAYER FOR SOLAR CELL APPLICATION

Uma Ghorpade,Mahesh Suryawanshi,Seung Wook Shin,K. V. Gurav,S. A. Patil,B. S. Pawar,M. G. Gang,Sanjay Kolekar,Jin Hyeok Kim 한국신재생에너지학회 2014 AFORE Vol.2014 No.-

ENABLING UNASSISTED VISIBLE SOLAR WATER SPLITTING VIA GREEN AND EFFICIENT EUTECTIC MEDIATED QUANTUM DOT SENSITIZED PHOTOELECTRODES

Uma V. Ghorpade,Jin Hyeok Kim 한국신재생에너지학회 2017 AFORE Vol.2017 No.11

Studies on the influence of etching solution on the properties of Cu₂ZnSn(S,Se₄) thin film solar cells

Shim, Hong Jae,Ghorpade, Uma V.,Surywanshi, Mahesh P.,Gang, Myengil,Kim, Jin Hyeok Elsevier 2019 THIN SOLID FILMS - Vol.670 No.-

<P><B>Abstract</B></P> <P>Cu<SUB>2</SUB>ZnSn(S,Se)<SUB>4</SUB> (CZTSSe) thin film solar cells (TFSCs) have emerged as the most promising low-cost alternatives to well-established CuInGaS<SUB>2</SUB> and CuInS<SUB>2</SUB>-based TFSCs technologies. The surface composition of the absorber layer and the interface quality between the absorber and buffer layers play a key role in the performance of CZTSSe TFSCs. In this study, we investigated the influence of different etchants namely potassium cyanide (KCN), hydrochloric acid (HCl) and ammonia on different properties such as structural, morphological, and compositional as well as the solar cell performance of CZTSSe TFSCs. The results revealed no significant changes in the film structural properties before and after etching with any of the tested etchants. However, the slight changes in the composition and microstructure were observed after etching treatment. The microstructure was improved after KCN treatment with larger grain size compared to absorber layer without etching, whereas the slightly distorted microstructure with several surface pinholes was observed after HCl and ammonia treatment. Surprisingly, HCl and ammonia treatments degraded the open circuit voltage and fill factor values and thereby decreasing the power conversion efficiency (PCE) of the CZTSSe TFSCs. On the other hand, KCN treatment slightly improved the PCE of CZTSSe TFSCs. The decreased PCE after HCl and ammonia treatments could be mainly attributed to the deteriorated absorber quality as well as poor formation of poor juction between the absorber layer and the CdS buffer layer.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Comparative study of different etchants has been conducted on CZTSSe solar cells. </LI> <LI> KCN etching improved the performance of CZTSSe solar cells. </LI> <LI> HCl and NH<SUB>4</SUB>OH degraded the performance of CZTSSe solar cells. </LI> </UL> </P>

A Simple Aqueous Precursor Solution Processing of Earth-Abundant Cu₂SnS₃ Absorbers for Thin-Film Solar Cells

Suryawanshi, Mahesh P.,Ghorpade, Uma V.,Shin, Seung Wook,Pawar, Sachin A.,Kim, In Young,Hong, Chang Woo,Wu, Minhao,Patil, Pramod S.,Moholkar, Annasaheb V.,Kim, Jin Hyeok American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.18

<P>A simple and eco-friendly method of solution processing of Cu2SnS3 (CTS) absorbers using an aqueous precursor solution is presented. The precursor solution was prepared by mixing metal salts into a mixture of water and ethanol (5:1) with monoethanolamine as an additive at room temperature. Nearly carbon-free CTS films were formed by multispin coating the precursor solution and heat treating in air followed by rapid thermal annealing in S vapor atmosphere at various temperatures. Exploring the role of the annealing temperature in the phase, composition, and morphological evolution is essential for obtaining highly efficient CTS-based thin film solar cells (TFSCs). Investigations of CTS absorber layers annealed at various temperatures revealed that the annealing temperature plays an important role in further improving device properties and efficiency. A substantial improvement in device efficiency occurred only at the critical annealing temperature, which produces a compact and void-free microstructure with large grains and high crystallinity as a pure-phase absorber layer. Finally, at an annealing temperature of 600 degrees C, the CTS thin film exhibited structural, compositional, and microstructural isotropy by yielding a reproducible power conversion efficiency of 1.80%. Interestingly, CTS TFSCs exhibited good stability when stored in an air atmosphere without encapsulation at room temperature for 3 months, whereas the performance degraded slightly when subjected to accelerated aging at 80 degrees C for 100 h under normal laboratory conditions.</P>

Solution Processed Porous Fe₂O₃ Thin Films for Solar-Driven Water Splitting

Suryawanshi, Mahesh P.,Kim, Seonghyeop,Ghorpade, Uma V.,Suryawanshi, Umesh P.,Jang, Jun Sung,Gang, Myeng Gil,Kim, Jin Hyeok,Moon, Jong Ha Materials Research Society of Korea 2017 한국재료학회지 Vol.27 No.11

We report facile solution processing of mesoporous hematite (${\alpha}-Fe_2O_3$) thin films for high efficiency solar-driven water splitting. $Fe_2O_3$ thin films were prepared on fluorine doped tin oxide(FTO) conducting substrates by spin coating of a precursor solution followed by annealing at $550^{\circ}C$ for 30 min. in air ambient. Specifically, the precursor solution was prepared by dissolving non-toxic $FeCl_3$ as an Fe source in highly versatile dimethyl sulfoxide(DMSO) as a solvent. The as-deposited and annealed thin films were characterized for their morphological, structural and optical properties using field-emission scanning electron microscopy(FE-SEM), X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS) and UV-Vis absorption spectroscopy. The photoelectrochemical performance of the precursor (${\alpha}-FeOOH$) and annealed (${\alpha}-Fe_2O_3$) films were characterized and it was found that the ${\alpha}-Fe_2O_3$ film exhibited an increased photocurrent density of ${\sim}0.78mA/cm^2$ at 1.23 V vs. RHE, which is about 3.4 times higher than that of the ${\alpha}-FeOOH$ films ($0.23mA/cm^2$ at 1.23 V vs. RHE). The improved performance can be attributed to the improved crystallinity and porosity of ${\alpha}-Fe_2O_3$ thin films after annealing treatment at higher temperatures. Detailed electrical characterization was further carried out to elucidate the enhanced PEC performance of ${\alpha}-Fe_2O_3$ thin films.

FABRICATION OF Cu₂SnS₃ THIN FILM SOLAR CELLS USING CU/SN LAYERED METALLIC PRECURSORS PREPARED BY SPUTTERING PROCESS

Ju Yeon Lee,In Young Kim,Uma V. Ghorpade,Dong Seon Lee,Jin Hyeok Kim 한국신재생에너지학회 2015 AFORE Vol.2015 No.11

A facile, one-step electroless deposition of NiFeOOH nanosheets onto photoanodes for highly durable and efficient solar water oxidation

Suryawanshi, Mahesh P.,Shin, Seung Wook,Ghorpade, Uma V.,Kim, Jihun,Jeong, Hye Won,Kang, Soon Hyung,Kim, Jin Hyeok The Royal Society of Chemistry 2018 Journal of materials chemistry. A, Materials for e Vol.6 No.42

<P>A low-cost, highly efficient and durable photoelectrochemical (PEC) water-splitting system can be realized through designing a hierarchical core/shell nanostructured photoanode entirely composed of Earth-abundant elements. Herein, we report the rational design of a core/shell nanostructured photoanode with a TiO2 nanorod (NR) array as the core and a highly active Earth-abundant NiFe oxyhydroxide ((Ni1−xFex)OOH, NiFeOOH) oxygen evolution catalyst (OEC) as the shell for PEC water oxidation. Specifically, the NiFeOOH nanosheets were prepared <I>via</I> a facile, one-step electroless deposition method for a short reaction time of 10 min at room temperature. The TiO2/NiFeOOH core/shell nanostructured photoanode exhibits an unprecedented enhancement in photocurrent density (3.85 mA cm<SUP>−2</SUP> at 1.23 V <I>vs.</I> a reversible hydrogen electrode, (RHE)), no decay in photocurrent density over 24 h, and an obvious cathodic onset potential shift of 133 mV compared to the TiO2 NRs (0.73 mA cm<SUP>−2</SUP> at 1.23 V <I>vs.</I> RHE). The electron transfer mechanism is discussed through electrochemical impedance spectroscopy studies and calculated band alignments <I>via</I> ultraviolet photoelectron spectroscopy characterization. This work not only suggests a simple, room temperature electroless strategy for integrating Earth-abundant catalysts with photoanodes, but also accelerates the development of rationally designed core/shell photoanodes for efficient and durable solar water oxidation.</P>

Tailor-made dicationic ionic liquid as a fluorescent sensor for detection of hydroquinone and catechol

Patil, Sandip K.,Patil, Suryakant A.,Vadiyar, Madagonda M.,Awale, Deepak V.,Sartape, Ashish S.,Walekar, Laxman S.,Kolekar, Govind B.,Ghorpade, Uma V.,Kim, Jin H.,Kolekar, Sanjay S. Elsevier 2017 Journal of molecular liquids Vol.244 No.-

<P>We are exploring a geminal dicationic ionic liquid (DCIL), 1,1'-(propane-1,3-diyl)bis(4-aminopyridin-1-ium) dihydroxide, [C-3(Amp)(2)][OH](2) as a fluorescent probe for detection of dihydroxybenzenes viz. hydroquinone (HQ) and catechol (CC). Simple and sensitive spectrofluorometric method is described which accomplished with efficient quenching of fluorescence of aqueous DCIL by dihydroxybenzenes. The sensor offers good linear detection range of 1-400 mu M and 1-1000 mu M with detection limits of 0.31 mu M and 0.40 mu M for HQ and CC, respectively. Under alkaline conditions HQ/CC oxidizes to corresponding benzoquinones which interact with DCIL and consequently quenching of fluorescence is occurred. This essential alkaline condition is in situ provided by purposefully tuned DCIL to having basic nature. The plausible quenching mechanism that involves photo-induced charge transfer pathway is evidently discussed. The proposed method is competent over a broad detection range. Selectivity of method is demonstrated by scrutinizing intervention of various interfering species. Recoveries from water sample analysis emphasize the possible use of DCIL probe in the detection of HQ and CC from water sources. The proposed method certainly confers a new approach in sensing techniques for dihydroxybenzenes. (C) 2017 Published by Elsevier B.V.</P>