Dip coating of Cu2ZnSn(SxSe1-x)4 Absorber Layer for Solar Photovoltaic Applications

Chaudhari, Sushmita and Dey, Suhash Ranjan (2018) Dip coating of Cu2ZnSn(SxSe1-x)4 Absorber Layer for Solar Photovoltaic Applications. PhD thesis, Indian Institute of Technology Hyderabad.

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Abstract

Photon absorber layer plays a crucial role in inorganic photovoltaic solar cells. For achieving high efficiency with less material usage, absorber layer should be a direct band gap material with large absorption coefficient. Among all direct band gap inorganic thin film solar cells, CIGS based solar cell has achieved the maximum efficiency of 22.6% at lab scale. Toxic nature and less availability of its constituents in earth crust’s limit its large scale utilization, and thus solar cells based on kesterite mineral structure, like Cu2ZnSn(SxSe1-x)4 (CZTSSe) have gained interest in the emerging thin-film solar cell research field. Cu2ZnSn(SxSe1-x)4 (CZTSSe), a quaternary chalcogenide is an appropriate replacement of CIGS and CdTe absorber layers in thin film single junction solar cell as it is composed of all earth abundant and non-toxic elements and have direct band gaps which varies from 1.0 eV to 1.5 eV with large absorption coefficient (~104 cm−1 ). It is originated from CuInS2 by isoelectronic replacement of indium (In) with zinc (Zn) and tin (Sn) and thus have quite comparable properties like CuInS2 without the presence of toxic and expensive elements. The main aim of the present research is the fabrication of CZTSSe thin film through cost-effective and industrially viable solution based non-vacuum dip coating technique using hydrazine free precursor solution to avoid toxicity and any accidental harms that are possible during the fabrication process. After dip coating of the substrate into the precursor solution, heat treatment of dip coated CZTS precursor film is needed to form CZTS film. Variation in annealing parameters aids in better control over the composition of individual elements, morphology and crystallinity of kesterite CZTS thin-films. The ratio of Cu:Zn:Sn:S present in the precursor film and annealing conditions control the chemical potential and thus formation enthalpy of CZTS. Chemical potential control is very important in case of kesterite structure owing to narrow thermodynamics window. To achieve phase-pure CZTS thin-film, influence of different annealing parameters (temperature, holding time, annealing rate and atmosphere) on formation of CZTS is studied. Optimization of annealing parameters result in the minimization of undesired viii secondary phases in the as annealed CZTS films and leads to the formation of uniform, phase-pure CZTS thin film with the required composition through a simple hydrazine free precursor solution. In addition, controlling the reaction among Cu-Zn-Sn-thiourea precursors in the solution is also a major concern in formation of phase-pure CZTS. Thus, investigations on effects of addition of amount of stabilizing agent triethanolamine (TEA) on formation of CZTS thin films through dip coating technique have been carried out. In the proposed work, triethanolamine (TEA) is used as a stabilizing agent in the precursor solution. The purpose of addition of stabilizing agent is to form a complex molecule with the metallic precursor to inhibit the reaction among them. As a result, addition of stabilizing agent controls the rate of reaction and also maintains the uniformity of the films. But, further addition of higher concentration leads to non- uniformity and secondary phases. Along with this, due to optimization of annealing parameters and concentration of stabilizing agent into the precursor solution, conventional sulfurization step can be avoided and uniform, crystalline films can be fabricated by annealing the CZTS precursor film in N2 environment. Furthermore, formation of phase-pure, Zn rich CZTSSe films with S/(S+Se) ~30% by selenization of dip coated CZTS precursor films in presence of elemental Se powder is achieved by incorporation of Se into the film.

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IITH Creators:
IITH CreatorsORCiD
Dey, Suhash Ranjanhttp://orcid.org/0000-0002-5148-9534
Item Type: Thesis (PhD)
Uncontrolled Keywords: Thin Film, Solar Cell
Subjects: Materials Engineering > Materials engineering
Divisions: Department of Material Science Engineering
Depositing User: Team Library
Date Deposited: 21 Jun 2018 12:01
Last Modified: 21 Jun 2018 12:01
URI: http://raiith.iith.ac.in/id/eprint/4060
Publisher URL:
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