Thin-Film FTO-ZnO-CZTS Solar Cells Fully Deposited by Spray Pyrolysis

Salif Cisse

doi:10.11648/j.ajmsp.20190401.11

Abstract

Thin films of ZnO, CZTS (Cu2ZnSnS4) and ZnO-CZTS were prepared by spray pyrolysis deposition (SPD). After spraying a precursor solution of ZnO directly onto fluorine-doped tin oxide (FTO) substrats, CZTS thin layers were sprayed onto layers of ZnO to forme a p-n junction. Some CZTS layers were directly spray onto fluorine-doped tin oxide substrats. ZnO is a wide band gap n-type material, consisting of abundant and nontoxic elements, and is thus expected to be a good substitute for CdS buffer layer in solar cells. In this paper, we report the study of CZTS and ZnO thin films synthesized by chemical spray pyrolysis (CSP) method. During the deposition of the ZnO thin films on the FTO substrats the number of sequences was varied from 20 to 40. The influence of the ZnO on the structural, optical, morphological and electrical properties of CZTS films was studied using various techniques. The X-ray diffraction studies showed the formation of kesterite (Cu2ZnSnS4) phases with the peaks corresponding to (112), (220) and (312) planes. SEM study revealed a lack of uniformity of the surface of the CZTS layers sprayed onto the ZnO layers for a lower thickness of ZnO (FTO-ZnO20-CZTS). The band gap values of FTO-CZTS and FTO-ZnO-CZTS thin films were measured and found in the range 2.2 - 2.25 eV which are in good agreement with the results reported (2-2.2 eV). The morphological studies revealed the formation of some clusters randomly distributed on the film surface in the ZnO-containing layers, i.e. the FTO-ZnO20-CZTS and Finally, current-voltage measurements for different PV cells with maximum efficiency were carried out. A conversion efficiency (η) of 5.99% with fill factor (FF) = 18.8%, open circuit voltage (Voc) = 0.54 V, short circuit current density (Jsc) = 59 mA.cm2 were recorded through the FTO-ZnO40-CZTS thin film PV cell.

Highlights

One of the proposed ways for reducing the cost per watt is to reduce the manufacturing cost of the photovoltaic cell, to considerably reduce the amount of semiconductor materials in the composition of the cell and increase its lifetime
In order to achieve this, we investigated the structural and optical properties of CZTS, ZnO thin films synthesized by spray pyrolysis deposition (SPD)
To identify the crystalline phases in the films deposited by SPD, X-ray diffraction (XRD) was carried out

Summary

Introduction

One of the proposed ways for reducing the cost per watt is to reduce the manufacturing cost of the photovoltaic cell, to considerably reduce the amount of semiconductor materials in the composition of the cell and increase its lifetime. Since Cd is a highly toxic element, an alternative material is needed for the buffer layer to get a more environmental friendly device. In order to overcome these problems, several types of ternary and quaternary semiconductors can be proposed in the form of thin layers. Among the most promising ternary semiconductors for the manufacture of thin-film solar cells are copper indium gallium diselenide CuInGaSe2 denoted CIGSe, in its chalcopyrite form. Note the toxicity of selenium (Se) and scarcity of indium (In) and gallium (Ga) [1]

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Conclusion