CZTS thin film solar cells on flexible Molybdenum foil by electrodeposition-annealing route

Abstract

Earth-abundant and non-toxic Kesterite-based Cu2ZnSnS4 (CZTS) thin film solar cells are successfully fabricated on flexible Molybdenum (Mo) foil substrates by an electrodeposition-annealing route. A well-adherent, densely packed, homogeneous, compact, and mirror-like CZT precursor is initially produced through electrodeposition by using a rotating working electrode. Subsequently, the co-electrodeposited CuZnSn (CZT) precursor is sulfurized in quartz tube furnace at 550 °C for 2 h in N2 atmosphere with the presence of elemental sulfur in order to form CZTS. Different characterization techniques like XRD, SEM, HR-TEM, Raman, and Photoluminescence demonstrate that almost phase-pure CZTS formed after sulfurization. A flexible Al/Al-ZnO/i-ZnO/CdS/CZTS/Mo foil solar cell is produced, where CdS is deposited by chemical bath deposition and transparent conducting oxide (TCO) is deposited by DC sputtering. The CZTS solar device shows a 0.55% power conversion efficiency on flexible Mo foil substrate and it constitutes the first prototype of this kind of solar cell produced by electrodeposition-annealing route without any surface modification of the Mo substrate. Graphic abstract

One-step CZT electroplating from alkaline solution on flexible Mo foil for CZTS absorber

“…The deposition was performed using AMEL 2553 Potentiostat/ Galvanostat under galvanostatic conditions (−2.3 mA cm −2 , 10 min). The co-electrodeposition bath was developed through the optimization of the work of Khalil et al [18][19][20] and comprised 230 mM of K 4 P 2 O 7 , 15 mM of CuCl 2 , 35 mM of ZnSO 4 , 15 mM of EDTA-Na 2 , 10 mM of SnCl 2 , pH = 10 adjusted with NH 4 OH. Soft (300°C, 90 min) and reactive (560°C, 20 min) annealing were carried out using a singlezone tubular furnace using N 2 as inert/carrier gas.…”

Growth and Characterization of Stoichiometric Cu2ZnSnS4 Crystal Using Vertical Bridgman Technique

“…One of the most important reasons for this is the difficulty in growing this quaternary material due to the existence of volatile constituent elements, as well as the narrow phase stability region for the desired kesterite CZTS, which can easily decompose into binary and ternary secondary phases with a slight deviation in the stoichiometry. [ 6,20 ] It is, therefore, challenging to grow high quality CZTS crystals with the desired stoichiometry owing to the aforementioned factors. As they are developed by a peritectic reaction (liquid phase + ZnS) or a solid state conversion during the cooling stage, it is particularly challenging to grow high‐quality single crystals of the CZTS from a melt.…”

Fabrication of CZTS Solar Cells Using Electrodeposition Techniques

“…ITO has the disadvantage of containing indium, which, as explained previously, is a relatively scarce and costly material. The purpose of the TCO layer is to aid the transition of electrons to the metal top contact [141] (which is not shown in the diagram in Figure 1-6): The metal top contact is a fine metal grid, usually aluminium or nickelaluminium deposited via thermal or electron beam evaporation [142,143,144,145],…”

“…It also does not require any toxic or volatile solvents as the electrolytes are typically aqueous. Pure sulphide CZTS cells of up to 8.7% efficiency have been achieved using this technique [175], and it has been evidenced that it can be used to deposit CZTS onto flexible substrates [145]. Electrodeposition (or electroplating) is already established as a large scale commercial process and is used extensively in the steel industry [176].…”

“…When precursors are deposited via electrodeposition, it is essential that they undergo a reactive annealing (sulphurisation) process in order for CZTS to form. Different types of furnaces can be used to perform this reactive anneal, such as rapid thermal processing/annealing (RTP/RTA) furnaces [203], tube furnaces [145], or standard convection furnaces (in which the annealed sample would be placed inside a quartz ampoule [200]). In addition to the type of furnace, there are other variables that can be adjusted, such as the type of inert gas used (typically nitrogen [204] or argon [205]), the background pressure (if using a closed system) [206], the gas flow rate (if using a gas flow system) [207], whether a source of tin is included to reduce tin evaporation [201], the source and quantity [206] of sulphur/selenium (which can be elemental sulphur/selenium [206] or hydrogen sulphide gas [204,205]), and the temperature-time profile [208].…”