Current Enhancement via a TiO2 Window Layer for CSS Sb2Se3 Solar Cells: Performance Limits and High V _oc

Abstract

Antimony selenide (Sb 2 Se 3) is an emerging chalcogenide photovoltaic absorber material that has been the subject of increasing interest in recent years, demonstrating rapid efficiency increases with a material that is simple, abundant, and stable. This paper examines the material from both a theoretical and practical standpoint. The theoretical viability of Sb 2 Se 3 as a solar photovoltaic material is assessed and the maximum spectroscopically limited performance is estimated, with a 200 nm film expected to be capable of achieving a photon conversion efficiency of up to 28.2%. By adapting an existing CdTe close-spaced sublimation (CSS) process, Sb 2 Se 3 material with large rhubarb-like grains is produced and solar cells are fabricated. We show that the established CdS window layer is unsuitable for use with CSS, due to intermixing during higher temperature processing. Substituting CdS with the more stable TiO 2 , a power conversion efficiency of 5.5% and an open-circuit voltage V o c of 0.45 V are achieved; the voltage exceeding current champion devices. This paper demonstrates the potential of CSS for scalable Sb 2 Se 3 deposition and highlights the Manuscript

Chemical etching of Sb2Se3 solar cells: surface chemistry and back contact behaviour

“…where C is a fitting parameter, R Ω0 is the Ohmic resistance, and k is the Boltzmann constant. As shown by Al Turkestani [30], at low temperature the exponential term is much greater than the first two terms Hence, for this experiment, the third term is deemed sufficient and the expression is simplified to: Similar to SEM analysis, XRD patterns ( figure 3) show no significant differences between the samples, with all three patterns showing prominent peaks at 28.2°, 31.2°, 32.2°and 45.6°that are characteristic of the (211), (221), (301) and (002) planes respectively (using the Pbnm space-group labelling convention [11]). These planes are representative of nanoribbons lying at 37°, 44°, 46°and 0°from normal to the substrate for the (211), (221), (301) and (002) planes respectively.…”

“…Even the ∼45°angle of the (221) and (301) planes from normal is not expected to impede carrier transport due to the size of the grains in this material. It is reasonable to assume that the majority of the grains, and therefore the nanoribbons, span from the bottom to the top of the film [2,11]. There is a small difference in the peak at 26.6°, however this is attributed to an additional Sb 2 Se 3 (021) orientation [2] and is therefore not indicative of any significant change at the surface.…”

“…Impressive device efficiencies have been achieved with a range of device structures and both with and without a variety of interfacial layers. [7][8][9][10] Previous work has shown that device performance depends strongly on the orientation of the nanoribbons in the film and, thus far, a large fraction of work on this material has focused on optimising growth conditions to achieve optimal orientation [4][5][6][10][11][12]. As a result there are many aspects of material and device behaviour that are still poorly understood, such as front and back contacting.…”

The complex defect chemistry of antimony selenide

“…4 Prior theoretical calculations have reaffirmed the optimal band gap and absorption, 5,6 while calculation of thin-lm efficiency metrics have demonstrated particularly high and promising values for Sb 2 Se 3 , even for very thin layers of material. 7,8 Prior to the past few years, Sb 2 Se 3 was most of interest for use in 'extremely thin absorber' (ETA) cells, as a sensitizer to TiO 2 , however efficiencies remained near 3%. [9][10][11][12] Over the past ve years, however, creation of heterojunction cells, with careful control of growth conditions to align the Sb 2 Se 3 chains perpendicular to the substrate, and optimization of the junction interface has rapidly improved cell performance, with a recently published record efficiency of 9.2%, 13 cementing it as a highly promising PV material.…”

Benchmark performance of low-cost Sb2Se3 photocathodes for unassisted solar overall water splitting

“…As Sb 2 Se 3 has a one-dimensional (1D) crystal structure, it tends to grow with the morphology of 1D nanostructures, which makes synthesis of compact Sb 2 Se 3 thin films difficult 28 . In the case wherein a light-absorbing material has a low absorption coefficient and poor electrical properties (e.g.…”