Cu₂ ZnSnSe₄ thin film solar cells above 5% conversion efficiency from electrodeposited Cu Sn Zn precursors

Abstract

Cu2ZnSnSe4 solar cells were synthesized by electrodeposition of metal stack precursors followed by selenization, a high potential process for industry, leading to conversion efficiencies above 5%. An additional selenium‐capping layer deposited on the precursor before annealing showed improved uniformity and morphology of CZTSe layers compared to other selenization routes. Two different atmospheric annealing systems were used: a closed graphite box in a tubular furnace and a three‐chamber dynamic rapid thermal processing furnace. The RTP system gave larger grains and more compact layers, whereas CZTSe selenized in tube furnace had smaller grains and a higher series resistance. Both annealing systems gave best cells power conversion efficiencies over 5%. We will discuss the device photoelectric properties and their relation to material structures and processing.

Co-Electrodeposition of Metallic Precursors for the Fabrication of CZTSe Thin Films Solar Cells on Flexible Mo Foil

“…[18][19][20][21] MoSe 2 (JCPDS 29-0914) which usually forms at the interface between CZTSe and bottom Mo layer was observed at diffraction angles 31.2…”

“…During Raman measurement, 514.5 nm excitation wavelength of laser source was used, so penetration depth of laser source could be in the range of 150 nm according to the studies of Fernandes et al 24 Raman spectra reveal three Raman peaks corresponding to CZTSe at 172 cm −1 , 195 cm −1 and 234 cm −1 Raman shift along with most intense peak at 195 cm −1 which are in agreement with the previous studies. [18][19][20][21] No peak corresponding to any secondary phases of Cu 2 Se, Cu 2 SnSe 3 or SnSe was observed, suggesting the formation of pure crystalline CZTSe phase. The atomic chemical composition of selenized film by scanning electron microscope equipped with EDS is also in agreement with the pure crystalline CZTSe phase.…”

Fabrication of CZTS Solar Cells Using Electrodeposition Techniques

“…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].…”

“…This avoids all of the sulphur/selenium being evaporated and lost in the early stages of the annealing process and provides a continuous supply of vapours. It is also possible to have third temperature zone that the sulphur/selenium vapours pass through to reach the precursor sample [203]. This can be set to a higher temperature than the precursor sample in order to act as a "cracking" zone, in which the vapour particles break up into individual molecules.…”

“…This can be set to a higher temperature than the precursor sample in order to act as a "cracking" zone, in which the vapour particles break up into individual molecules. An example of such a setup can be seen in Figure 1-12, which has been taken from [203]. In addition to the reactive anneal, many publications also report a pre-anneal, sometimes referred to as a soft anneal or a pre-alloying step, in which the precursor is annealed without the presence of sulphur or selenium in order to encourage the intermixing of the metallic elements [146,179,210,211].…”