Characterization of electronic structure of oxysulfide buffers and band alignment at buffer/absorber interfaces in Cu(In,Ga)Se₂-based solar cells

Abstract

Galaxies' rest-frame ultraviolet (UV) properties are often used to directly infer the degree to which dust obscuration affects the measurement of star formation rates (SFRs). While much recent work has focused on calibrating dust attenuation in galaxies selected at rest-frame ultraviolet wavelengths, locally and at high-z, here we investigate attenuation in dusty, star forming galaxies (DSFGs) selected at far-infrared wavelengths. By combining multiwavelength coverage across 0.15-500 μm in the COSMOS field, in particular making use of Herschel imaging, and a rich data set on local galaxies, we find an empirical variation in the relationship between the rest-frame UV slope (β) and the ratio of infrared-to-ultraviolet emission (L IR /L UV ≡ IRX) as a function of infrared luminosity, or total SFR. Both locally and at high-z, galaxies above SFR 50 M yr −1 deviate from the nominal IRX-β relation toward bluer colors by a factor proportional to their increasing IR luminosity. We also estimate contamination rates of DSFGs on high-z dropout searches of 1% at z 4-10, providing independent verification that contamination from very dusty foreground galaxies is low in Lyman-break galaxy searches. Overall, our results are consistent with the physical interpretation that DSFGs, e.g., galaxies with >50 M yr −1 , are dominated at all epochs by short-lived, extreme burst events, producing many young O and B stars that are primarily, yet not entirely, enshrouded in thick dust cocoons. The blue rest-frame UV slopes of DSFGs are inconsistent with the suggestion that most DSFGs at z ∼ 2 exhibit steady-state star formation in secular disks.

Electronic structures of Cu2ZnSnSe4surface and CdS/Cu2ZnSnSe4heterointerface

“…In contrast, the energy difference (|CBM CIGS | − |VBM CIGS |) for CIGS with a carrier concentration of 10 16 cm −3 is more than +0.3 eV. [21][22][23][24] The surface features of CZTSe and CIGS are quite different. In particular, the Fermi level in our CZTSe was positioned near the center of the bandgap, which could be one of the features of kesterite materials.…”

CIGS photovoltaics: reviewing an evolving paradigm

“…It is nevertheless well-established that sulfur alloying tends to increase the electron affinity and bandgap energy relative to pure selenides [68]. This is an important consideration for ESC optimization because sulfur-containing buffers can result in significant alloying of the CIGS absorber [69].…”

“…Oxygen can also affect absorber grain boundary passivation. Atmospheric exposure before ESC fabrication has impacts on band alignment and recombination [84], and it can incorporate during CBD of buffer layers as hydroxyl groups [68]. A recent review discusses these issues in considerable detail [92].…”

Sputtered Inx(O,S)y Buffer Layers for Cu(In,Ga)Se2 Thin-Film Solar Cells: Engineering of Band Alignment and Interface Properties

“…In contrast to the interface properties, tailoring the band alignment to improve the cell performance is relatively unexplored. The conduction band offsets (Δ E C ) of the In-based buffer/CIGSe interface were reported in a wide range from −0.45 to 0.5 eV ,− and strongly depend on the growth methods of buffer layers. The O-doped In 2 S 3 thin films have been fabricated by using various methods, including thermal evaporation, ALD, and CBD processes. − Their results suggest that doping O into the In 2 S 3 layer can enlarge the band gap and modify the conduction band minimum, which is beneficial to the band alignment with CIGSe absorbers; , however, these studies only focus on the growth mechanism and/or fundamental properties of deposited films without reporting device performance.…”