Wide band gap semiconductors are essential for today's electronic devices and energy applications because of their high optical transparency, controllable carrier concentration, and tunable electrical conductivity. The most intensively investigated wide band gap semiconductors are transparent conductive oxides (TCOs), such as tin-doped indium oxide (ITO) and amorphous In-Ga-Zn-O (IGZO), used in displays and solar cells, carbides (e.g., SiC) and nitrides (e.g., GaN) used in power electronics, and emerging halides (e.g., γ-CuI) and 2D electronic materials (e.g., graphene) used in various optoelectronic devices. Compared to these prominent materials families, chalcogen-based (Ch = S, Se, Te) wide band gap semiconductors are less heavily investigated but stand out because of their propensity for p-type doping, high mobilities, high valence band positions (i.e., low ionization potentials), and broad applications in electronic devices such as CdTe solar cells. This manuscript provides a review of wide band gap chalcogenide semiconductors. First, we outline general materials design parameters of high performing transparent semiconductors, as well as the theoretical and experimental underpinnings of the corresponding research methods. We proceed to summarize progress in wide band gap (E_G > 2 eV) chalcogenide materials-namely, II-VI MCh binaries, CuMCh₂ chalcopyrites, Cu₃MCh₄ sulvanites, mixed-anion layered CuMCh(O,F), and 2D materials-and discuss computational predictions of potential new candidates in this family, highlighting their optical and electrical properties. We finally review applications-for example, photovoltaic and photoelectrochemical solar cells, transistors, and light emitting diodes-that employ wide band gap chalcogenides as either an active or passive layer. By examining, categorizing, and discussing prospective directions in wide band gap chalcogenides, this Review aims to inspire continued research on this emerging class of transparent semiconductors and thereby enable future innovations for optoelectronic devices.

The original version of the article contained a number of problems related to references that may lead to error propagation in the scientific literature. We would like to correct these issues, and sincerely apologize to the readers and reference authors for any confusion they might have caused. 1. ref 120 should be replaced with ref 146 to indicate ZnSe band gap, in section 2.2.2 2. ref 132 should be replaced with ref 131 to indicate ZnS lattice matching to other materials, in section 3.1.1 3. ref 136 claims electrical conductivity of ∼10−5 S cm−1 for 3% Cu doped ZnS rather than for 0.1% Cu doped ZnS, in section 3.1.1 4. ref 148 claims conductivity of 0.06 S cm−1 and mobility of 86 cm2 V−1 s−1 instead of 0.02 S cm−1 and mobility of 13 cm2 V−1 s−1, respectively, for NSe doped ZnSe in section 3.1.1 (also in Table 1) 5. ref 163 and ref 67 should be cited for ∼3.5 and ∼3.0 eV band gaps of ZB and WZ MgTe respectively, in Table 1 6. ref 163, ref 225, and ref 226 to support data of intrinsic In2S3 in addition to ref 227, in Table 1 7. ref 171 claims p-type conduction due to Mn vacancy in RS instead of WZ phase of MnS, in Table 1 8. ref 188 claims conductivities up to ∼1550 S cm−1 instead of 50 S cm−1 in In-doped CdS (also in Table 1), and ref 187 is to In doping in CdTe, in section 3.1.4 9. ref 249 should read “Bhandari, R. K.; Hashimoto, Y.; Ito, K. CuAlS2 Thin-Films Prepared by Sulfurization of Metallic Precursors and their Properties. Jpn. J. Appl. Phys., 2004, 43 (10), 6890−6893”, in section 3.3.1. 10. ref 268 should be added to GeGa and SnGa defects in its following sentence, and TiGa defect should be referred to “Palacios, P.; Aguilera, I.; Wahnon, P.; Conesa J. C. Thermodynamics of the Formation of Ti- and Cr-doped CuGaS2 Intermediate-band Photovoltaic Materials. J. Phys. Chem. C 2008, 112 (25), 9525−9529”, in section 3.3.1 11. ref 276 claims 2.2 to 2.5 eV instead of 2.5 to 2.7 eV, as experimental gap of AgAlSe2, in section 3.3.2 12. ref 305 and ref 306 should be swapped; ref 305 should refer to ionic conductivity, and ref 306 should refer to the electronic structure of Cu3TaS4, in section 3.4.2 13. ref 308 and ref 309 should be swapped, where ref 309 should refer to synthesis and ref 308 should refer to band gap of Cu3NbSe4, respectively, in section 3.4.2 14. ref 325 claims 2.6 eV instead of 2.2−2.6 eV as the gap for K2Hg3S4, in section 3.4.5 15. ref 327 should be added to ref 326 for the band gap of Cu3SbS3, and the band gaps of Li3SbS3, Na3SbS3, and Ca2Sb2S5 should refer to “Bhattacharya, S.; Chmielowski, R.; Dennler, G.; Madsen, G. K. H. Novel ternary sulfide thermoelectric materials from high throughput transport and defect calculations. J. Mater. Chem. A 2016, 4 (28), 11086−11093”, in section 3.4.6 16. ref 345 claims the field-effect mobility of CuSCN to be 0.01−0.1 cm2 V−1 s−1 instead of 0.001−0.1 cm2 V−1 s−1, in section 3.5.3 17. ref 360 is to band gaps of CsYZnSe3, CsSmZnSe3, and CsErZnSe3, and ref 357 is with respect to band gaps of BaYCuS3, BaNdCuS3, and BaNdAgS3, in section 3.5.6 18. ref 424 refers to the previous sentence about bulk As2S3 material; instead the sentence about As2S3 monolayer, indirect gap, strain, and thickness should refer to “Debbichi, L.; Kim, H.; Björkman, T.; Eriksson, O.; Lebegue S. First-principles investigation of two-dimensional trichalcogenide and sesquichalcogenide monolayers. Phys. Rev. B 2016, 93, 245307” and “Miao, N.; Zhou, J.; Sa, B.; Xu, B.; Sun, Z. Few-layer arsenic trichalcogenides: Emerging two-dimensional semiconductors with tunable indirect−direct band-gaps. J. Alloys Compd. 2017, 699, 554−560”, in section 3.6.2 19. ref 478 and ref 479 should be swapped, where ref 478 refers to theoretical predictions for CdSe, ZnS, ZnSe, and ZnTe, and ref 479 refers to experimental observations of Ga in CuInSe2, in section 4.1.2 20. ref 504 and ref 277 discuss AgAlTe2 and AgAlSe2 instead of AgGaTe2 and AgGaSe2, respectively, and CuAlSe2 instead of CuAlS2 should be referenced to ref 269 in the same sentence, in section 4.1.3.

As thin-film cadmium telluride (CdTe) solar cells gain prominence, one particular challenge is optimizing contacts and their interfaces to transfer charge without losses in efficiency. Back contact recombination is still significant and will prevent CdTe solar technology from reaching its full potential in device efficiency, and transparent back contacts have not been developed for bifacial solar technology or multijunction solar cells. To address these challenges, this study investigates sputtered CuxZn1-xS as a p-type semi-transparent back contact material to thin-film polycrystalline CdTe solar cells at Cu concentrations x = 0.30, 0.45, and 0.60. This material is selected for its high hole conductivity (160-2120 S cm-1), wide optical band gap (2.25-2.75 eV), and variable ionization potential (approximately 6-7 eV) that can be aligned to that of CdTe. We report that without device optimization, CdTe solar cells with these CuxZn1-xS back contacts perform as well as control cells with standard ZnTe:Cu back contacts. We observe no reduction in external quantum efficiency, low contact barrier heights of approximately 0.3 eV, and carrier lifetimes on par with those of baseline CdTe. These cells are relatively stable over one year in air, with VOC and efficiency of the x = 0.30 cell decreasing by only 1 and 3%, respectively. Using scanning electron microscopy and scanning transmission electron microscopy to investigate the CuxZn1-xS/CdTe interface, we demonstrate that the CuxZn1-xS layer segregates into a bilayer of Cu-Te-S and Zn-Cd-S, and thermodynamic reaction calculations support these findings. Despite its bilayer formation, the back contact still functions well. This investigation explains some of the physical mechanisms governing the device stack, inspires future work to understand interfacial chemistry and charge transfer, and elicits optimization to achieve higher-efficiency CdTe cells.