Cu2ZnSnS4 Thin Film Solar Cells Research Articles

Solution-processed Cu2ZnSnS4 superstrate solar cell using vertically aligned ZnO nanorods

One-dimensional (1D) zinc oxide (ZnO) nanostructures are considered to be promising materials for use in thin film solar cells because of their high light harvesting and charge collection efficiencies. We firstly report enhanced photovoltaic performances in Cu2ZnSnS4 (CZTS) thin film solar cells prepared using ZnO nanostructures. A CdS-coated, vertically well-aligned ZnO nanorod (NR) array was prepared via a hydrothermal reaction and nanocrystal layer deposition (NCLD) and was used as a transparent window/buffer layer in a CZTS thin film photovoltaic. A light absorber CZTS thin film was prepared on the CdS/ZnO NRs in air by depositing a non-toxic precursor solution that was annealed in two steps at temperatures up to 250 °C. The crystallized CZTS phase completely infiltrated the CdS/ZnO NR array. The nanostructured ZnO array provided improved light harvesting behavior compared to a thin film configuration by measuring UV–vis transmittance spectroscopy. The prepared CZTS/CdS/ZnO NR device exhibited a solar energy conversion efficiency of 1.2%, which is the highest efficiency yet reported for nanostructured superstrate CZTS solar cells.

A Review on Development Prospect of CZTS Based Thin Film Solar Cells

Cu2ZnSnS4is considered as the ideal absorption layer material in next generation thin film solar cells due to the abundant component elements in the crust being nontoxic and environmentally friendly. This paper summerized the development situation of Cu2ZnSnS4thin film solar cells and the manufacturing technologies, as well as problems in the manufacturing process. The difficulties for the raw material’s preparation, the manufacturing process, and the manufacturing equipment were illustrated and discussed. At last, the development prospect of Cu2ZnSnS4thin film solar cells was commented.

Characterization of a CZTS thin film solar cell grown by sputtering method

We report the performance of Cu2ZnSnS4 (CZTS) thin film solar cell that showed efficiency in the range of 6.2% without an anti-reflection coating. Initially, the CZTS precursor film was co-sputtered using three different targets; copper (Cu), tin sulfide (SnS) and zinc sulfide (ZnS). The Cu target was subjected to DC power, and RF power was used for the SnS and ZnS targets. The as-grown CZTS film was sulfurized in a H2S/N2 environment at 525°C, which re-crystalized the film with grain sizes in the range of 1μm. Cadmium sulfide (CdS) was used as the n-type layer. Current–voltage (I–V), quantum efficiency (QE) and capacitance–voltage (C–V) measurements were used to characterize the cell device. The modeling and analysis of QE and CV data showed that a significant portion of the CZTS layer did not contribute to the photo-generation. Optimizing CZTS phase purity, improving QE in the broader wavelength region, and increasing minority carrier lifetime are necessary steps to further improve CZTS device performance.

Effects of sulfurization temperature on CZTS thin film solar cell performances

Synthesis of Cu2ZnSnS4 thin film solar cells by sulfurization of sputtered Sn/Zn/Cu precursors is studied. The sulfurization temperatures were varied, and the morphology, cross section, and composition of the CZTS were investigated by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and Raman scattering. To further explore the CZTS layer, the following additional layers were deposited to complete the solar cells: CdS with chemical bath deposition; ZnO and AZO with RF magnetron deposition; and, finally, silver fingers as the front contact. The efficiency and characteristics of the thin film solar cells were measured and a detailed comparison is reported. Sulfurization at 550°C yields a maximum efficiency of 5.75% without any anti-reflective layers.

Laser assisted electro-deposition of earth abundant Cu2ZnSnS4 photovoltaic thin film

In this study, we introduce laser assisted electro-deposition (LAED) to deposit earth abundant Cu2ZnSnS4 (CZTS) thin film solar cell material at room temperature and atmospheric pressure. It is found LAED results in much denser and larger CZTS crystals. Laser induced local photo-electrochemical reaction significantly increases the electro-deposition rate. The thermal effect of laser irradiation also improves the CZTS thin film quality by reducing the internal defects such as grain boundaries and inter-crystal gaps. An almost stoichiometric composition for the manufactured CZTS film. A post laser crystallization is applied to further improve crystal quality.

Effects of sulphurization time on Cu2ZnSnS4 absorbers and thin films solar cells obtained from metallic precursors

We report the results of a study of the sulphurization time effects on Cu2ZnSnS4 absorbers and thin film solar cells prepared from dc-sputtered stacked metallic precursors. Three different time intervals, 10min, 30min and 60min, at maximum sulphurization temperature were considered. The effects of this parameter' change were studied both on the absorber layer properties and on the final solar cell performance. The composition, structure, morphology and thicknesses of the CZTS layers were analyzed. The electrical characterization of the absorber layer was carried out by measuring the transversal electrical resistance of the samples as a function of temperature. This study shows an increase of the conductivity activation energy from 10meV to 54meV for increasing sulphurization time from 10min to 60min. The solar cells were built with the following structure: SLG/Mo/CZTS/CdS/i-ZnO/ZnO:Al/Ni:Al grid. Several ac response equivalent circuit models were tested to fit impedance measurements. The best results were used to extract the device series and shunt resistances and capacitances. Absorber layer's electronic properties were also determined using the Mott–Schottky method. The results show a decrease of the average acceptor doping density and built-in voltage, from 2.0×1017cm−3 to 6.5×1015cm−3 and from 0.71V to 0.51V, respectively, with increasing sulphurization time. These results also show an increase of the depletion region width from approximately 90nm–250nm.

An alternative route towards low-cost Cu2ZnSnS4 thin film solar cells

A non-vacuum and low-cost route to fabrication of Cu2ZnSnS4 (CZTS) thin film as absorber layer for thin film solar cell is demonstrated. The process involves synthesis of Cu–Zn–Sn composite oxide nanoparticles, preparation of composite oxide ink, deposition of composite oxide thin film and subsequent sulfurization treatment. Cu–Zn–Sn composite oxide nanoparticles with proper composition and particle size can be obtained by controlling the chemical co-precipitation conditions. The effects of sulfurization temperature on the compositional, structural, morphological, optical and electrical properties of the CZTS thin films were investigated. XRD, Raman and X-ray photoelectron spectroscopy analyses confirmed the formation of CZTS phase after sulfurization. The prepared CZTS thin films exhibit porous morphology and an optical band gap about 1.35eV. The solar cells fabricated with the CZTS thin film sulfurized at 550°C showed a conversion efficiency of 1.22%.

The Effect of a Heating Rate on the Properties of Cu2ZnSnS4 Thin Films Solar Cells

The effect of the heating rate during the sulfurization process on the properties of Cu2ZnSnS4 (CZTS) thin film solar cells was investigated. A moderate heating rate of ~10 oC/min was found to result in a modest solar cell performance (2 %), whereas the higher heating rates resulted in worse performances. In the CZTS thin films annealed with the highest heating rate, the segregation of Cu atoms towards the outer surface of the films, which is believed to lead to shunting of the solar cells.

Study of the junction and carrier lifetime properties of a spray-deposited CZTS thin-film solar cell

The Cu2ZnSnS4 (CZTS) thin-film solar cell fabricated entirely by a spray pyrolysis process was investigated under diffused white light in the present study. A CdS layer was developed as a heterojunction partner. The structural, morphological and photovoltaic characterization of an as-prepared stoichiometric CZTS film was carried out. The diode ideality factor n was found to be in the range of 1.2–5.6 in the forward bias region and it is explained by the Frenkel–Poole conduction model. The solar cell exhibited open-circuit voltage (Voc) of 157.25 mV, short-circuit current density (Jsc) of 3.024 mA cm−2 and fill factor (FF) of 24.77% at an incident irradiance of 200 W m−2 from the white LED source. The effective minority carrier lifetime of 263 μs was confirmed by the open-circuit voltage decay fitting under pulsed monochromatic LED excitation.

Enhancement of output performance of Cu2ZnSnS4 thin film solar cells—A numerical simulation approach and comparison to experiments

Abstract The formation of stable, low resistance and nonrectifying contacts to Cu 2 ZnSnS 4 (CZTS) thin film photovoltaic material are the major and critical challenges associated with its effect over the output performance of fabricated solar cells. The solution of continuity equation in one dimension for a soda lime glass substrates (SLG) |Mo | CZTS | CdS | ZnO:Al cell structure is considered in the simulation of its current–voltage characteristics that is governed by the back contact material, acceptor concentration as well as thickness of the CZTS layer. Our primary simulation shows a 6.44% efficiency of the CZTS solar cell which is comparable to reported experimental data if these parameters are not optimized. However, by optimizing them a simulated conversion efficiency as high as 13.41% ( V oc =1.002 V, J sc =19.31 mA/cm 2 , fill factor ( FF )=69.35%) could be achievable. The solar cell with a back contact metal work function of 5.5 eV, an absorber layer's thickness of 2.68 μm and an acceptor concentration of 5×10 16 cm −3 were optimum. The presented optimization is ideal and subject to experimental verification with a precise control of the process parameters along with reduced surface as well as bulk recombination, secondary phases and thermalization losses.

Admittance spectroscopy of Cu2ZnSnS4 based thin film solar cells

In this report, we propose an AC response equivalent circuit model to describe the admittance measurements of Cu2ZnSnS4 thin film solar cell grown by sulphurization of stacked metallic precursors. This circuit describes the contact resistances, the back contact, and the heterojunction with two trap levels. The study of the back contact resistance allowed the estimation of a back contact barrier of 246 meV. The analysis of the trap series with varying temperature revealed defect activation energies of 45 meV and 113 meV. The solar cell’s electrical parameters were obtained from the J-V curve: conversion efficiency, 1.21%; fill factor, 50%; open circuit voltage, 360 mV; and short circuit current density, 6.8 mA/cm2.

Impact of KCN etching on the chemical and electronic surface structure of Cu2ZnSnS4 thin-film solar cell absorbers

The chemical and electronic surface structure of Cu2ZnSnS4 thin-film solar cell absorbers has been investigated by direct and inverse photoemission. Particular emphasis was placed on the impact of KCN etching, which significantly alters the surface composition and is best explained by a preferred etching of Cu and, to a lesser degree, Sn. As a consequence the surface band gap increased from (1.53 ± 0.15) eV, which agrees with optically derived bulk band gap values, to (1.91 ± 0.15) eV.

Native oxidation and Cu-poor surface structure of thin film Cu2ZnSnS4 solar cell absorbers

Air-exposed Cu2ZnSnS4 (“CZTS”) thin-film solar cell absorbers have been investigated by surface-sensitive x-ray photoelectron and x-ray-excited Auger electron spectroscopy, as well as by bulk-sensitive energy dispersive x-ray spectroscopy. We find a native surface oxidation of (mainly) tin, but also (to a lesser extent) of zinc and sulfur as well as evidence for a Cu-poor region at the surface of the absorber, best described by a Cu-free Zn-Sn-S surface layer.

Identification of Impurity Phases in Cu2ZnSnS4 Thin-film Solar Cell Absorber Material by Soft X-ray Absorption Spectroscopy

ABSTRACTThe composition of Cu2ZnSnS4 thin-film solar cell absorbers was varied to induce the.formation of secondary impurity phases. For their identification, the samples have been investigated by Cu L3 and S L2,3 soft x-ray absorption (XAS) spectroscopy. We find that Cu L3 XAS is especially sensitive to the presence of copper sulfides as well as copper oxides and/or changes in the electron configuration, suggesting a basis for future studies of the surface, defect, and interface characterization of similar samples. Additionally, it is shown that the S L2,3 absorption data can be used as a very sensitive probe of the variations in the prevalence of S-Zn bonds in the near-surface region of the investigated samples.