N-type Buffer Layer Research Articles

Defect characterization of heavy-ion irradiated AlInN/GaN on Si high-electron-mobility transistors

The characteristic energies of traps in InAlN/AlN/GaN high-electron mobility transistor structures on Si(111) substrates formed after irradiation with 75 MeV S-ions are studied by means of c-lattice parameter analysis, vertical IV-characteristics, micro-photoluminescence (µ-PL), photocurrent (PC) and thermally stimulated current (TSC) spectroscopy. From the lattice parameter analysis, point defect formation is concluded to be the dominant source of defects upon irradiation. A strong compensation effect manifests itself through enhanced resistivity of the devices as found in vertical IV-measurements. Defect formation is detected optically by an additional PL-band within the green spectral region, while defect states with threshold energies at 2.9 eV and 2.65 eV were observed by PC spectroscopy. The TSC spectra exhibit two defect-related emissions between 300 K and 400 K with thermal activation energies of 0.78–0.82 eV and 0.91–0.98 eV, respectively. The data further supports the formation of Ga vacancies (V Ga) and related complexes acting mainly as acceptors compensating the originally undoped n-type GaN buffer layers after irradiation.

Properties of sputter-grown CuGaS2 absorber and CuGaS2/Cd1-xZnxS buffer heterointerface for solar cell application

In realizing wide-bandgap CuGaS2 (CGS) based solar cells, CGS thin film deposition methods and suitable n-type buffer layers need to be studied. Even though CGS belongs to the same chalcopyrite family as the more extensively-studied Cu(In,Ga)Se2, their different nature of defects and band profile require a different thin-film deposition approach as well as a careful tuning of the band alignment at the p-n heterojunction. This study focuses on the material properties of sputter-grown CGS films as absorber layer and the heterointerface between CGS absorber and Cd1-xZnxS buffer layer. A moderate amount of Zn is found to be effective in widening the bandgap of the buffer layer while suppressing undesirable absorption loss of high energy photons. Improved optical and structural properties and photocurrent generation are observed from solar cell structure with a sputter-grown CGS absorber with Cd1-xZnxS buffer layer.

Pulse electrodeposited zinc sulfide as an eco-friendly buffer layer for the cadmium-free thin-film solar cells

Zinc sulfide (ZnS) is an emerging alternate n-type buffer layer for the cadmium-free thin-film solar cells. The present research adopts a unique mixture of glycerol and tartaric acid for the emergence of phase-pure ZnS during pulse electrodeposition . Besides, proper optimization of pulse parameters aid in producing crystalline ZnS films with no post-deposition heat treatment. The as-deposited films exhibit cubic ZnS as confirmed from X-Ray Diffraction (XRD) and micro-Raman analyses. The optical study reveals an average transmittance of 71% in the wavelength spread of 300–900 nm with a band gap of 3.8 eV. The n-type semiconducting behavior of ZnS is affirmed from the Mott-Schottky analysis and the flat band potential is inferred to be −1.0 V vs SCE . The crystalline ZnS films produced from the economic pulse electrodeposition method devoid of heat treatment step, with their demonstration as photoanode in photoelectrochemical cells are suitable for the relevant applications. • A room temperature electrodeposition process for ZnS with better control over the morphology and composition. • Phase-pure ZnS is obtained using pulse electrodeposition with no post heat-treatment. • A novel method using a blend of organic reagents, tartaric acid and glycerol in the electrolyte.

Towards Highly Efficient Chalcopyrite Photocathodes for Water Splitting: The Use of Cocatalysts beyond Pt.

Solar radiation is a renewable and clean energy source used in photoelectrochemical cells (PEC) to produce hydrogen gas as a powerful alternative to carbon-based fuels. Semiconductors play a vital role in this approach, absorbing the incident solar photons and converting them into electrons and holes. The hydrogen evolution reaction (HER) occurs in the interface of the p-type semiconductor that works as a photocathode in the PEC. Cu-chalcopyrites such as Cu(In, Ga)(Se,S)2 (CIGS) and CuIn(Se,S)2 (CIS) present excellent semiconductor characteristics for this purpose, but drawbacks as charge recombination, deficient chemical stability, and slow charge transfer kinetics, demanding improvements like the use of n-type buffer layer, a protective layer, and a cocatalyst material. Concerning the last one, platinum (Pt) is the most efficient and stable material, but the high price due to its scarcity imposes the search for inexpensive and abundant alternative cocatalyst. The present Minireview highlighted the use of metal alloys, transition metal chalcogenides, and inorganic carbon-based nanostructures as efficient alternative cocatalysts for HER in PEC.

(Invited) Potentials and Challenges of Wide Bandgap Copper Chalcopyrite Thin Film Absorbers for Photoelectrochemical Water Splitting Applications

Photoelectrochemical (PEC) water splitting has the potential to become an efficient method for renewable hydrogen production. However, the efficiency, projected cost, and durability of lab-scale systems are not yet at the level required to make this technology economically feasible. Amongst all materials studied to date, the chalcopyrite class is arguably one of the best classes for PEC water splitting, as it has already demonstrated low-cost and high photoconversion capabilities as a photovoltaic material. In the context of PEC, our group has shown that co-evaporated 1.65 eV bandgap (EG) CuGaSe2 is capable of evolving hydrogen with Faradaic efficiency greater than 85% and generate photocurrent densities over 15 mA.cm-2, as measured in a 3-electrode configuration in 0.5M H2SO4 under simulated AM1.5G illumination. Unfortunately, CuGaSe2’s narrow EG limits its integration as top absorber into a dual junction stacked PEC device (also known as hybrid photoelectrode, HPE). In the present communication, we report on our latest efforts to synthesize wide-EG (1.8-2.0 eV) chalcopyrites, compatible with the HPE integration scheme, and capable of generating saturated photocurrent densities greater than 10 mA/cm2. We present specifically results on EG tunable Cu(In,Ga)(S,Se)2, Cu(In,Ga)S2, CuGa(S,Se)2 and CuGa3Se5. We also discuss some of the strategies developed to improve their surface energetics for the hydrogen evolution reaction, including the use of bandgap tunable MgZnO n-type buffer layers. We also include recent durability testing of chalcopyrite photocathodes coated with metal oxide protection layers. Finally, we present solid-state techniques and theoretical modeling used by our team to identify possible pitfalls in these material systems and discuss potential paths for improvement.

Depth profile of acceptor concentration in InGaN/GaN multiple quantum wells

Zn contamination of InGaN/GaN multiple quantum well (MQW) structure from unknown source is found. A model describing concentration profile of Zn acceptor impurity in InGaN/GaN MQW structure is introduced and compared to measured values. The model is based on difference among the formation energies of acceptors in the InGaN quantum wells. A nice correlation of the model and experimental data helps to reveal origin of Zn impurity in InGaN quantum wells. Proposed methodology can be applied to different acceptor-like defects and shine light the upon enigma of high defect concentration in the bottom quantum wells grown atop the n-type buffer layer.

Accumulation-Mode Lateral Double-Diffused MOSFET Breaking Silicon Limit by Eliminating Dependence of Specific ON-Resistance on Doping Concentration

An accumulation-mode lateral double-diffused MOSFET (LDMOS) is proposed and its mechanism is investigated in this article. To optimize the tradeoff between breakdown voltage (BV) and specific ON-resistance ( ${R}_{\text {on,sp}}$ ), the idea of separating the breakdown area from the conduction path is designed. The N-type buffer layer is adopted to obtain ideal reverse characteristics for accumulation-mode LDMOS. The electrons are introduced to eliminate the dependence of the ${R}_{\text {on,sp}}$ on the doping concentration of the drift region. Simulation results show that the ${R}_{\text {on,sp}}$ of the proposed LDMOS is 6.83 $\text{m}\Omega \cdot \text {cm}^{{2}}$ with the BV of 460 V, which is less than 30.2 $\text{m}\Omega \cdot \text {cm}^{{2}}$ that of the conventional LDMOS with the BV of 223 V for the same drift region length of $20~\mu \text{m}$ . Moreover, the ${R}_{\text {on,sp}}$ of ac-NBL LDMOS is only 2.07 $\text{m}\Omega \cdot \text {cm}^{{2}}$ , which is reduced by 93% compared with the conventional LDMOS with the same BV of 223 V. A better tradeoff between BV and ${R}_{\text {on,sp}}$ can be obtained by eliminating the dependence of ${R}_{\text {on,sp}}$ on the doping concentration, and the ${R}_{\text {on},\text {sp}}$ of ac-NBL LDMOS increases much more slowly than that of conventional LDMOS as BV increases.

Influence of Cd0.6Zn0.4S buffer layer on the band alignment and the performance of CZTS thin film solar cells

The CdS film is one of the best candidates for the n-type buffer layer in Cu 2 ZnSnS 4 (CZTS) solar cells. However, the inappropriate band alignment at CdS/CZTS heterojunction result in the high barrier for the photogenerated carriers, which decrease the open-circuit voltage and the short-circuit current. In this paper, the crystallization and the optical bandgap of the Zn-doping Cd 0.6 Zn 0.4 S film fabricated by chemical bath deposition were studied. XRD showed that the lattice constant of hexagonal Cd 0.6 Zn 0.4 S decreased a little after Zn doping because of the shorter bond length of Zn–S. Photoluminescence and transmittance spectra showed the band gap of Cd 0.6 Zn 0.4 S thin film increased from 2.59 to 2.88 eV due to Burstein-Moss shift. The conduction band offset (CBO) obviously decreased from 0.51 eV in CZTS/CdS heterojunction to 0.27 eV in CZTS/Cd 0.6 Zn 0.4 S heterojunction which result in the short-circuit current increasing from 12.25 to 15.05 mA/cm 2 . The conversion efficiency (E ff ) and fill factor (FF) of the solar cell based on CZTS/Cd 0.6 Zn 0.4 S were increased from 2.31% to 31.06 to 4.88% and 47.45, comparing to CZTS/CdS solar cell. • The effects of the Zn-doping Cd 0.6 Zn 0.4 S film fabricate of Cu 2 ZnSnS 4 thin film solar cells were studied in detail. • To our knowledge, the (CBO) decreased from 0.51 eV in CZTS/CdS heterojunction to 0.27 eV in CZTS/Cd 0.6 Zn 0.4 S heterojunction. • The best Eff. of the fabricated CZTS/Cd 0.6 Zn 0.4 S thin film solar cell is 4.88% with the V oc of 628 mV, J sc of 15.05 mA/cm 2 .

Photoelectrochemical CO2 Reduction Using CuInS2 Photocathode Modified with CdS and Noble Metal Catalysts

Photoelectrochemical CO2 reduction using sunlight is a promising approach to producing a clean energy carrier that could replace fossil fuels, providing a sustainable future energy supply. Copper chalcopyrite compounds, Cu(In,Ga)(S,Se)2, have recently received considerable attention as promising candidates for photocathodes owing to their high absorption coefficients and high carrier mobilities, and efficient photoelectrochemical H2 production using a series of Cu(In,Ga)(S,Se)2-based photocathodes has been demonstrated. Moreover, the photoelectrochemical performance of these photocathodes has been reported to improve when combined with n-type semiconductor buffer layers due to the formation of a p–n junction, which facilitates charge separation at the interface. Meanwhile, noble metal catalysts have been widely used to catalyze redox reactions efficiently because they can lower the overpotential for desirable reactions. Especially, some Au and Ag catalysts have been reported to proceed highly efficient and selective electrochemical CO2 reduction. Based on these backgrounds, in this study, we investigated photoelectrochemical CO2 reduction using CuInS2 electrode modified with CdS buffer layer and noble metal catalysts.CuInS2 thin film electrodes were synthesized on Mo foil using electrodeposition and subsequent sulfurization. The electrode surface was modified with CdS by chemical bath deposition method, followed by photoelectrochemical deposition of Pt, Au, and Ag. As shown in Figure, the prepared photoelectrodes showed distinct photocurrent generation under visible light irradiation. Modification with noble metal catalysts was effective to enhance the photoresponse and the photocurrent density increased in the order of Pt > Au > Ag. As a result of photoelectrolysis at -0.1 V vs RHE in CO2-saturated NaHCO3 solution, generation of CO was confirmed from all the electrodes although the Faradaic efficiency was different depending on the noble metal catalysts. Details will be discussed at the conference.

(Invited) Synthesis and Integration of Wide Bandgap Chalcopyrite Candidates for Photoelectrochemical Water Splitting Applications

Photoelectrochemical (PEC) water splitting has the potential to become an efficient method for renewable hydrogen production. However, the efficiency, projected cost, and durability of lab-scale systems are not yet at the level required to make this technology economically feasible. Amongst all materials studied to date, the chalcopyrite class is arguably one of the most promising classes for PEC water splitting, as it has already demonstrated low-cost and high photoconversion capabilities as a photovoltaic material. In the context of PEC, our group has shown that co-evaporated 1.65 eV bandgap (EG) CuGaSe2 is capable of evolving hydrogen with Faradaic efficiency greater than 85% and generate photocurrent densities over 15 mA.cm-2, as measured in a 3-electrode configuration in 0.5M H2SO4 under simulated AM1.5G illumination. Unfortunately, CuGaSe2’s narrow EG limits its integration as top absorber into a dual junction stacked PEC device (also known as hybrid photoelectrode, HPE). In the present communication, we report on our latest efforts to synthesize wide-EG (1.8-2.0 eV) chalcopyrites, compatible with the HPE integration scheme, and capable of generating saturated photocurrent densities greater than 10 mA/cm2. We present specifically results on EG tunable Cu(In,Ga)(S,Se)2, Cu(In,Ga)S2, CuGa(S,Se)2 and CuGa3Se5. We also discuss some of the strategies developed to improve their surface energetics for the hydrogen evolution reaction, including the use of bandgap tunable MgZnO n-type buffer layers. We also include recent durability testing of chalcopyrite photocathodes coated with metal oxide protection layers. Finally, we present solid-state techniques and theoretical modeling used by our team to identify possible pitfalls in these material systems and discuss potential paths for improvement.

High colloidal stability ZnO nanoparticles independent on solvent polarity and their application in polymer solar cells

Significant aggregation between ZnO nanoparticles (ZnO NPs) dispersed in polar and nonpolar solvents hinders the formation of high quality thin film for the device application and impedes their excellent electron transporting ability. Herein a bifunctional coordination complex, titanium diisopropoxide bis(acetylacetonate) (Ti(acac)2) is employed as efficient stabilizer to improve colloidal stability of ZnO NPs. Acetylacetonate functionalized ZnO exhibited long-term stability and maintained its superior optical and electrical properties for months aging under ambient atmospheric condition. The functionalized ZnO NPs were then incorporated into polymer solar cells with conventional structure as n-type buffer layer. The devices exhibited nearly identical power conversion efficiency regardless of the use of fresh and old (2 months aged) NPs. Our approach provides a simple and efficient route to boost colloidal stability of ZnO NPs in both polar and nonpolar solvents, which could enable structure-independent intense studies for efficient organic and hybrid optoelectronic devices.

Performance enhancement of ultrathin graded Cu(InGa)Se2 solar cells through modification of the basic structure and adding antireflective layers

Traditional Cu ( InGa ) Se2 (CIGS) solar cells consist of an Mo bottom contact, p-type CIGS absorber layer, n-type CdS buffer layer, and ZnO window layer including a very thin intrinsic ZnO layer topped with an Al-doped ZnO transparent conducting oxide layer that was simulated by an Silvaco technology computer aided design simulator. The thickness of the layers and other parameters were limited to the values reported in the literature. The simulator was examined to affirm its functionality, and a step-by-step method was applied to optimize the baseline structure. The first modification was the substitution of the conventional CdS buffer layer with a nontoxic n-type ZnO buffer layer. The substituted ZnO buffer layer showed an effective band alignment and led to a remarkable improvement in cell performance. The second modification was the inclusion of different antireflective coatings, such as Al2O3, MgO, SnO2, and CdO, to enhance light trapping. Among them, CdO caused the highest efficiency. The optimization process was followed by replacing a very-thin (750 nm) CIGS layer containing three sublayers with dual-graded Ga contents. A trapezoidal gradient profile was tested and showed a significantly increased internal electric field, which assisted in raising the efficiency of the device. The last simulation concluded that the efficiency of a CIGS solar cell was 19.21% and the efficiency related to the baseline structure was enhanced by 36.24%.

Strong performance enhancement in lead-halide perovskite solar cells through rapid, atmospheric deposition of n-type buffer layer oxides

Thin (approximately 10 nm) oxide buffer layers grown over lead-halide perovskite device stacks are critical for protecting the perovskite against mechanical and environmental damage. However, the limited perovskite stability restricts the processing methods and temperatures (<=110 C) that can be used to deposit the oxide overlayers, with the latter limiting the electronic properties of the oxides achievable. In this work, we demonstrate an alternative to existing methods that can grow pinhole-free TiOx (x = 2.00+/-0.05) films with the requisite thickness in <1 min without vacuum. This technique is atmospheric pressure chemical vapor deposition (AP-CVD). The rapid but soft deposition enables growth temperatures of >=180 {\deg}C to be used to coat the perovskite. This is >=70 {\deg}C higher than achievable by current methods and results in more conductive TiOx films, boosting solar cell efficiencies by >2%. Likewise, when AP-CVD SnOx (x ~ 2) is grown on perovskites, there is also minimal damage to the perovskite beneath. The SnOx layer is pinhole-free and conformal, which reduces shunting in devices, and increases steady-state efficiencies from 16.5% (no SnOx) to 19.4% (60 nm SnOx), with fill factors reaching 84%. This work shows AP-CVD to be a versatile technique for growing oxides on thermally-sensitive materials.

Defect limitations in Cu2ZnSn(S, Se)4 solar cells utilizing an In2S3 buffer layer

Alternative n-type buffer layer such as In2S3 has been proposed as a Cd-free alternative in kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. In this study, optical and electronic characterization techniques together with device analysis and simulation were used to assess nanoparticle-based CZTSSe absorbers and solar cells with CdS and In2S3 buffers. Photoluminescence spectroscopy indicated that CZTSSe absorbers with In2S3 buffer had a lower density of detrimental non-radiative defects and a higher concentration of copper vacancies VCu+, responsible for p-type conductivity in CZTSSe, in comparison to the absorber with CdS buffer. Capacitance–voltage (C–V) measurements revealed that the In2S3 buffer-based CZTSSe devices had a three times higher apparent doping density and a consequently narrower space charge region than devices with a CdS layer. This resulted in poorer collection of photo-generated charge carriers in the near-IR region despite a more favorable band alignment as determined by x-ray photoelectron and inverse photoelectron spectroscopy. The presence of interfacial defect states in In2S3 devices as determined by C–V and biased quantum efficiency measurements is also responsible for the loss in open-circuit voltage compared with reference devices with CdS.

Degradation of Mg-doped zinc oxide buffer layers in thin film CdTe solar cells

Cadmium Sulphide is the conventional n-type buffer layer used in thin film Cadmium Telluride solar cells. It is well known that Cadmium Sulphide causes optical losses and sulphur diffuses into the absorber during high temperature activation. Sputter-deposited Mg-doped ZnO (MZO) has been shown to be an attractive buffer layer for Cadmium Telluride solar cells due to its transparency and tuneable band gap. It is also stable to high temperature processing and avoids diffusion of elements into the cadmium telluride absorber during the cadmium chloride activation treatment. However, degradation is observed in solar cells incorporating MZO buffer layers. Analysis of the MZO film surface potential has revealed significant fluctuations in the thin film work function once the layer is exposed to the atmosphere following deposition. These fluctuations are attributed to the high reactivity to water vapour of the MgO contained in the MZO films. This has been analysed using X-ray Photoelectron Spectroscopy to determine corresponding changes in the surface chemistry. The Zinc Oxide component is relatively stable, but the analysis shows that MgO forms a Mg(OH)2 layer on the MZO surface which forms a secondary barrier at the MZO/CdTe interface and/or at the interface between MZO and the Fluorine-doped SnO2. This affects the Fill Factor and as a consequence it degrades the conversion efficiency.

(Invited) Emerging Chalcopyrite Photo-absorbers for Renewable Hydrogen Production

Photoelectrochemical (PEC) water splitting is an attractive method for efficient renewable hydrogen production. However, the cost, efficiency and durability of lab-scale systems are not yet at the level required to make this technology economically attractive. Amongst all materials studied to date, the chalcopyrite class is arguably one of the most promising classes for PEC water splitting, as it has already demonstrated low-cost and high photoconversion capabilities as a photovoltaic material. In the context of PEC, our group has shown that co-evaporated 1.65 eV bandgap (EG) CuGaSe2 is capable of evolving hydrogen with Faradaic efficiency greater than 85% and generate photocurrent densities over 15 mA.cm-­2, as measured in a 3-electrode configuration in 0.5M H2SO4 under simulated AM1.5G illumination. Unfortunately, CuGaSe2’s narrow EG limits its integration as top absorber into a dual junction stacked PEC device (also known as hybrid photoelectrode, HPE). In the present communication, we report on our latest efforts to synthesize wide-EG (1.8-2.0 eV) chalcopyrites, compatible with the HPE integration scheme, and capable of generating saturated photocurrent densities greater than 10 mA/cm2. We present specifically results on EG tunable Cu(In,Ga)S2, CuGa(S,Se)2 and CuGa3Se5. We also discuss some of the strategies developed to improve their surface energetics for the hydrogen evolution reaction, including the use of non toxic n-type buffer layers. We also include recent durability testing of chalcopyrite photocathodes coated with metal oxide protection layers. Finally, we present solid-state techniques and theoretical modeling used by our team to identify possible pitfalls in these material systems and discuss potential paths for improvement.

Controlled thickness of a chemical-bath-deposited CdS buffer layer for a SnS thin film solar cell with more than 3% efficiency

Tin monosulfide (SnS) is considered a promising earth-abundant absorber material for thin film solar cells (TFSCs) with a theoretical power conversion efficiency (PCE) as high as 30%. However, the maximum PCE reported thus far is just 4.36%. This inferior device performance is attributed to low values of open-circuit voltage. In addition to the dense and pinhole-free surface morphology of the phase-pure p-type SnS thin film absorber, a controlled growth of the n-type buffer layer is a prerequisite for enhanced device performance. In this study, we explore the manner in which the thickness of a chemical-bath-deposited n-type CdS buffer layer influences the performance of SnS/CdS TFSCs. The thickness of the buffer layer was adjusted by varying the deposition time from 15 to 25 min, which resulted in thicknesses of 30–80 nm. Initially, the performance parameters of the TFSCs improved with the buffer layer thickness, but later deteriorated with thicker CdS layers. The highest PCE achieved was 3.05% at an optimized CdS buffer layer thickness of approximately 42 nm. This performance was accompanied by a significant decrease in reverse saturation current and shunt conductance, as evidenced by the current density–voltage characteristics under dark conditions.

Novel Superjunction LDMOS With a High-K Dielectric Trench by TCAD Simulation Study

A novel superjunction (SJ) lateral double-diffused MOSFET (LDMOS) with a deep High-K(HK) dielectric trench (HK SJ-LDMOS) is proposed and its mechanism is investigated by Technology Computer Aided Design (TCAD) simulations. The HK dielectric trench is embedded under the n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> drain, which is connected with the drain electrode. In the OFF-state, the reshaping effect of HK trench enhances the bulk electric field strength and weakens the peak electric field around the edge of the drain diffusion, which increases the breakdown voltage (BV). Moreover, because of the assistant depletion effect by the HK trench, a lower resistivity substrate is allowed for HK SJ-LDMOS, which also increases the doping concentration of the ntype buffer layer under the SJ layer of HK SJ-LDMOS, correspondingly. Thus, a lower specific ON-resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON,sp</sub> ) is also obtained. Simulation results show that the BV increases by 35.2% in comparison with the conventional buffered SJ-LDMOS with the same drift length. Moreover, HK SJ-LDMOS presents an excellent figure of merit, which is two times higher than that of the conventional buffered SJ-LDMOS.

Influence of the Thickness of a Layer of Potassium Fluoride Incorporated in the CIGS/CdS Interface on the Macroscopic Electrical Parameters of the Solar Cell

In this work, the heterojunction composed of a n-type ZnO transparent conductive oxide (OTC) layer, a n-type CdS buffer layer and a absorber layer based Cu (In, Ga)Se2 p doped is studied under the influence of a KF layer placed in the CIGS/CdS interface. This study was done by varying the thickness of KF using thin-film simulation software named SCAPS-1D. The presence of KF for a doping of the CIGS absorber of 1016cm-3 improves strongly the electrical parameters that are the Vco, the Jcc the FF, the maximum power and the conversion efficiency of the solar cell Ƞ. However, a decrease of the FF and the Jcc is noticed when the thickness of the KF is greater than 30nm causing a deterioration of the performances of the cell.

Effect of sulfurization temperature on optical and compositional properties of sputtered Zn(O, S) thin films

Zinc oxysulfide or Zn(O,S) is emerging as an alternate n-type buffer layer for kesterite, chalcogenides and CdTe based thin film solar cell due to it is being made from non-toxic elements and tunable bandgap, its suitable optical and electrical properties required for a buffer layer. Generally, buffer layers of these solar cells are deposited using chemical bath deposition (CBD) techniques, but these require breaking of vacuum and again inserting the sample in vacuum during solar cell fabrication, which is not economical and is cumbersome. Sputtering is considered to be industrial process and therefore, here we have deposited Zn(O,S) thin film by sputtering technique and effect of sulfurization temperature on bandgap and composition of Zn(O,S) films have been studied. The bandgap of deposited films changed from 3.36 eV to 3.15 eV by changing the sulfurization temperatures. By changing the sulfurization temperature, the composition of films also changed. Crystallite size (D) of Zn(O,S) films increased from 12.1 nm to 22.3 nm by varying the sulfur content for samples S1-S4, respectively. Optical, morphological, compositional and structural properties have been studied using UV-Vis-NIR spectroscopy, Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS) and X-ray diffractometer (XRD), respectively.