TaS₂ Back Contact Improving Oxide-Converted Cu₂BaSnS₄ Solar Cells

Abstract

Solar cells based on the wide band-gap Cu 2 BaSnS 4 (CBTS) photoabsorber have achieved open circuit voltages up to 1.1 V over a short development period, making CBTS an attractive material for tandem photovoltaic and photoelectrochemical cells. In this work, we explore an alternative CBTS growth route based on oxide precursors, and we propose TaS 2 as an alternative back contact material to the commonly used Mo/MoS 2 . The oxide precursor route does not require higher sulfurization temperatures than other more common fabrication routes, and it yields CBTS lms with negligible Stokes shift between photoluminescence maximum and band gap energy, while at the same time avoiding sulfur contamination of vacuum systems. The high work-function metallic TaS 2 compound is selected as a prospective hole-selective contact, which could also prevent the losses associated with carrier transport across the semiconducting MoS 2 layer. By comparing CBTS solar cells with Mo and TaS 2 back contacts, the latter shows 1 Page 1 of 29 ACS Paragon Plus Environment ACS Applied Energy Materials a signicantly lower series resistance, resulting in a 10% relative eciency improvement.Finally, we fabricate a proof-of-concept monolithic CBTS/Si tandem cell using a thin Ti(O,N) interlayer intended both as a diusion barrier and as a recombination layer between the two subcells.

Assessing the defect tolerance of kesterite-inspired solar absorbers

“…20,27,28 The elemental composition and sulfurization conditions of the films characterized in this work are those that gave the highestefficiency cells in the previous studies. 20,27,28 For all compounds, the bulk composition is Cu-poor and II-rich, and the sulfurization temperature is in the 520-560 1C range. For photoluminescence spectroscopy, the films were measured as-sulfurized without top Table 1 Selected properties of the kesterite-inspired compounds investigated in this study and of their constituent cations.…”

“…Paper analyzed in detail, 20,27,47 so in the next two sections we will discuss temperature-and excitation dependent PL measurements on our own CBTS and CSTS films.…”

“…This conclusion can explain the characteristic dip in the RT absorption coefficient of CBTS just above the band gap, which is typical of excitonic absorption 52 and has been observed in nearly all previous studies of CBTS. 18,19,27,47 If the RT absorption onset is due to excitonic absorption, band gap extraction by means of Tauc plots is not justified and leads to underestimation of the band gap. Fitting the absorption coefficient with an Elliott function is a more appropriate method to extract the band gap in the presence of excitonic absorption.…”

Recent Progress on Cu2BaSn(SxSe1–x)4: From Material to Solar Cell Applications

“…To reduce the interface recombination at the Mo/absorbers especially when there exists MoS 2 , Crovetto et al used TaS 2 as the back contact in the CBTS solar cell. [114] TaS 2 is helpful to form the ohmic contact due to its similar work function with that of CBTS. TaS 2 is also easily formed during the sulfurization process of Ta layer.…”

“…Reproduced with permission. [114] Copyright 2019, American Chemical Society. Reproduced with permission.…”