Natural Band Alignments and Band Offsets of Sb₂Se₃ Solar Cells

Abstract

Sb2Se3 is a promising material for use in photovoltaics, but the optimum device structure has not yet been identified. This study provides band alignment measurements between Sb2Se3, identical to that used in high-efficiency photovoltaic devices, and its two most commonly used window layers, namely, CdS and TiO2. Band alignments are measured via two different approaches: Anderson’s rule was used to predict an interface band alignment from measured natural band alignments, and the Kraut method was used in conjunction with hard X-ray photoemission spectroscopy to directly measure the band offsets at the interface. This allows examination of the effect of interface formation on the band alignments. The conduction band minimum (CBM) of TiO2 is found by the Kraut method to lie 0.82 eV below that of Sb2Se3, whereas the CdS CBM is only 0.01 eV below that of Sb2Se3. Furthermore, a significant difference is observed between the natural alignment- and Kraut method-determined offsets for TiO2/Sb2Se3, whereas there is little difference for CdS/Sb2Se3. Finally, these results are related to device performance, taking into consideration how these results may guide the future development of Sb2Se3 solar cells and providing a methodology that can be used to assess band alignments in device-relevant systems.

Ge 4s2 lone pairs and band alignments in GeS and GeSe for photovoltaics

“…The conduction band offset (CBO) between the window layer and absorber layer is an important factor in the performance of PV devices 25,26 . If the offset is positive, the conduction band of the window layer is higher than the absorber layer, and a 'spikelike' barrier forms which opposes the drift of excited electrons from absorber to window layer and thus limits the short-circuit current of the device.…”

Interface engineering of antimony selenide solar cells: a review on the optimization of energy band alignments

“…The formation of the band offsets is crucial to the performance of heterojunction solar cells. Generally, there are two types of band offsets at the heterojunction: type I ('spike-like') and type II ('cliff-like'), as displayed in figure 6 [51]. A 'spike-like' band offset (figure 6(a)) is formed when the CBM of an absorber layer lies below the CBM of a buffer or a window layer, while a 'cliff-like' band offset (figure 6(b)) describes the opposite situation.…”

Emerging Earth-Abundant Solar Absorbers

“…Band offsets are another important property which is now being explored in detail. Shiel et al used a novel photoemission method, utilizing two photon energies, to probe the band offset and curvature at the Sb 2 Se 3 –TiO 2 and Sb 2 Se 3 –CdS interfaces and suggested that while TiO 2 might act to prevent diffusion, it possesses a less favorable band offset with the absorber, compared with CdS; therefore, an alternative blocking layer may present additional opportunities for efficiency improvement …”

“…Shiel et al used a novel photoemission method, utilizing two photon energies, to probe the band offset and curvature at the Sb 2 Se 3 −TiO 2 and Sb 2 Se 3 −CdS interfaces and suggested that while TiO 2 might act to prevent diffusion, it possesses a less favorable band offset with the absorber, compared with CdS; therefore, an alternative blocking layer may present additional opportunities for efficiency improvement. 39 Computational Search for Novel Defect-Tolerant Solar Absorbers. Theory and computations have played a pivotal role in advancing our understanding of the defect tolerance features of hybrid perovskites and offered guidelines to search and design perovskite-inspired materials.…”