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The long search for nontoxic alternatives to lead halide perovskites (LHPs) has shown that some compelling properties of LHPs, such as low effective masses of carriers, can only be attained in their closest Sn(II) and Ge(II) analogues, despite their tendency toward oxidation. Judicious choice of chemistry allowed formamidinium tin iodide (FASnI3) to reach a power conversion efficiency of 14.81% in photovoltaic devices. This progress motivated us to develop a synthesis of colloidal FASnI3 NCs with a concentration of Sn(IV) reduced to an insignificant level and to probe their intrinsic structural and optical properties. Intrinsic FASnI3 NCs exhibit unusually low absorption coefficients of 4 × 103 cm-1 at the first excitonic transition, a 190 meV increase of the band gap as compared to the bulk material, and a lack of excitonic resonances. These features are attributed to a highly disordered lattice, distinct from the bulk FASnI3 as supported by structural characterizations and first-principles calculations., Nano Letters, 23 (5), ISSN:1530-6984, ISSN:1530-6992

Antimony sulfide (Sb2S3) is a promising light-absorbing semiconductor for photovoltaic applications, though it remains vastly unexplored for photoelectrochemical water splitting. Sb2S3 was synthesized by a simple sulfurization of electrodeposited antimony metal at relatively low temperatures (240–300 °C) with elemental sulfur. Using a TiO2 buffer layer and a platinum co-catalyst, photocurrent densities up to ∼9 mA cm–2 were achieved at −0.4 V vs RHE in 1 M H2SO4 under one sun illumination. Using X-ray photoelectron spectroscopy band alignment studies and potential-dependent incident photon-to-current efficiency measurements, a conduction band offset of 0.7 eV was obtained for the Sb2S3/TiO2 junction as well as an unfavorable band bending at the heterointerface, which explains the low photovoltage that was observed (∼0.1 V). Upon inserting an In2S3 buffer layer, which offers a better band alignment, a 0.15 V increase in photovoltage was obtained. The excellent photoelectrochemical water splitting performance and the identification of the origin of the low photovoltage of the Sb2S3 photocathodes in this work pave the way for the further development of this promising earth-abundant light-absorbing semiconductor for solar fuel generation.

TiO2 and WO3 are two of the most important, industrially relevant earth-abundant oxides. Although both materials show complementary functionality and are promising candidates for similar types of applications such as catalysis, sensor technology, and energy conversion, their chemical stability in reactive environments differs remarkably. In this study, anodic barrier oxides are grown on solid-solution WxTi1–x alloy precursors covering a wide compositional range (0 ≤ x ≤ 1) with the goal of creating functional oxides with tailored stability. A strong Ti-cation enrichment in the surface region of the grown WxTi1–xOn layer is observed, which can be controlled by both the anodizing conditions and precursor composition. For Ti concentrations above 50 at. %, a continuous nanometer-thick TiO2 protective coating is achieved on top of a homogeneous WxTi1–xOn film as evidenced by X-ray photoelectron spectroscopy and transmission electron microscopy analyses. A comprehensive electrochemical assessment demonstrates a very stable passivation of the surface in both acidic and alkaline environments. This increase in chemical stability correlates directly with the presence of this protective TiO2 film. The results of this work provide insights into the oxidation behavior of W1–xTix alloys, but more importantly demonstrate how controlled oxidation of self-passivating alloys can lead to oxide alloys with thin, protective surface layers that otherwise would require more sophisticated deposition methods.

Sb2Se3 has emerged as an important photoelectrochemical (PEC) and photovoltaic (PV) material due to its rapid rise in photoconversion efficiencies. However, despite its binary nature, Sb2Se3 has a complex defect chemistry, which reduces the maximum photovoltage that can be obtained. Thus, it is important to understand these defects and to develop passivation strategies in order to further improve this material. In this work, a comprehensive investigation of the charge carrier dynamics of Sb2Se3 and the influence of sulfur treatment on its optoelectronic properties was performed using time resolved microwave conductivity (TRMC), photoluminescence (PL) spectroscopy and low frequency Raman spectroscopy (LFRS). The key finding in this work is that upon sulfur treatment of Sb2Se3, the carrier lifetime is increased by the passivation of deep defects in Sb2Se3 in both the surface region and the bulk, which is evidenced by increased charge carrier lifetime of TRMC decay dynamics, increased radiative recombination efficiency and decreased deep defect level emission (PL), and improved long-range order in the material (LFRS). These findings provide crucial insights into the defect passivation mechanisms in Sb2Se3 paving the way for developing highly efficient PEC and PV devices.

Antimony sulfide (Sb2S3) is a promising light absorbing semiconductor for photovoltaic applications, though it remains vastly unexplored for photoelectrochemical water splitting. Sb2S3 was synthesized by a simple sulfurization of electrodeposited antimony metal at relatively low temperatures (240-300°C) with elemental sulfur. Using a TiO2 buffer layer and a platinum co-catalyst, photocurrent densities up to ~ 9 mA cm-2 were achieved at -0.4 V vs. RHE in 1 M H2SO4 under one sun illumination. Using XPS band alignment studies and potential dependent IPCE measurements, a conduction band offset of 0.7 eV was obtained for the Sb2S3/TiO2 junction as well as an unfavorable band bending at the heterointerface, which explains the low photovoltage that was observed (~ 0.1 V). Upon inserting an In2S3 buffer layer, which offers a better band alignment, a 0.15 V increase in photovoltage was obtained. The excellent PEC performance and the identification of the origin of the low photovoltage of the Sb2S3 photocathodes in this work pave the way for the further development of this promising earth abundant light absorbing semiconductor for solar fuels generation.

The identification of an effective copper–iron catalyst for the direct conversion of synthesis gas into higher alcohols is hindered by the low solubility limit of Cu in Fe and the limited understanding of structural and electronic descriptors in such multicomponent systems. Here, commercial carbonaceous carriers are shown to produce an efficient material only if they enable control of the size and location of metal species through confinement in adequately sized channels, with conical carbon nanofibers being more adequate than carbon nanotubes. Application of a sol–gel route was preferred to other deposition methods to avoid excessive Cu aggregation, associated with enhanced CO2 formation. A bulk Cu/Fe ratio of 2 permitted one to balance the different tendencies of Cu and Fe toward agglomeration, i.e., to form numerous Cu particles of moderate size and hinder the dispersion of the Fe phase and in turn the Fischer–Tropsch activity. Promotion by tiny amounts of potassium was instrumental to further increase...

Alloying of semiconductors with similar crystal structures is often used to fine-tune materials properties for optoelectronic applications. However, examples of semiconductor alloys between compounds with two different crystal structures, where properties are changing dramatically as a function of composition, are much rarer. Even more unusual are such heterostructural alloys where the structure and properties can be changed with only a small amount of substitution (

Optically transparent materials with p-type electrical conductivity can facilitate the development of transparent electronics and improve the efficiency of photovoltaic solar cells. Sulfide materials represent an interesting alternative to oxides for these applications due to better hole transport properties. Here, transparent and conductive Ba–Cu–S thin films are prepared by combinatorial cosputtering and characterized for their composition, structure, and optoelectronic properties. The conductivity and transparency of these films are found to be strongly dependent on their chemical composition and the substrate temperature during growth. The conductivity of BaCu2S2 and BaCu4S3 can reach 53 S/cm (at 250 °C) and 74 S/cm (at 200 °C), respectively, which is higher than their solution processed/bulk counterparts. The 90% reflectance corrected transmittance is achieved in the wavelength range 600–1000 nm for BaCu2S2 and 650–1000 nm for BaCu4S3 (at 250 °C). These electrical and optical properties are comparabl...

We report on design of optoelectronic properties in previously unreported metastable tin titanium nitride alloys with spinel crystal structure. Theoretical calculations predict that Ti alloying in metastable Sn3N4 compound should improve hole effective mass by up to 1 order of magnitude, while other optical bandgaps remains in the 1–2 eV range up to x ∼ 0.35 Ti composition. Experimental synthesis of these metastable alloys is predicted to be challenging due to high required nitrogen chemical potential (ΔμN ≥ +1.0 eV) but proven to be possible using combinatorial cosputtering from metal targets in the presence of nitrogen plasma. Characterization experiments confirm that thin films of such (Sn1–xTix)3N4 alloys can be synthesized up to x = 0.45 composition, with suitable optical band gaps (1.5–2.0 eV), moderate electron densities (1017 to 1018 cm–3), and improved photogenerated hole transport (by 5×). Overall, this study shows that it is possible to design the metastable nitride materials with properties su...

SnO exhibits electrical properties that render it promising for solar energy conversion applications, but it also has a strongly indirect band gap. Recent theoretical calculations predict that this disadvantage can be mitigated by isovalent alloying with other group II oxides, such as ZnO. Here, we have synthesized new metastable isovalent (Sn,Zn)O alloy thin films by combinatorial reactive co-sputtering and characterized their structural, optical, and electrical properties. The alloying of ZnO into SnO leads to a change of the valence state of the tin from Sn0 via Sn2+ to Sn4+, which can be counteracted by reducing the oxygen partial pressure during the deposition. The optical characterization of the smooth

Contact layers play an important role in thin film solar cells, but new material development and optimization of its thickness is usually a long and tedious process. A high-throughput experimental approach has been used to accelerate the rate of research in photovoltaic (PV) light absorbers and transparent conductive electrodes, however the combinatorial research on contact layers is less common. Here, we report on the chemical bath deposition (CBD) of CdS thin films by combinatorial dip coating technique and apply these contact layers to Cu(In,Ga)Se-2 (CIGSe) and Cu2ZnSnSe4 (CZTSe) light absorbers in PV devices. Combinatorial thickness steps of CdS thin films were achieved by removal of the substrate from the chemical bath, at regular intervals of time, and in equal distance increments. The trends in the photoconversion efficiency and in the spectral response of the PV devices as a function of thickness of CdS contacts were explained with the help of optical and morphological characterization of the CdS thin films. The maximum PV efficiency achieved for the combinatorial dip-coating CBD was similar to that for the PV devices processed using conventional CBD. The results of this study lead to the conclusion that combinatorial dip-coating can be used to accelerate the optimization of PV device performance of CdS and other candidate contact layers for a wide range of emerging absorbers.

Energy band alignments at heterointerfaces play a crucial role in defining the functionality of semiconductor devices, yet the search for material combinations with suitable band alignments remains a challenge for numerous applications. In this work, we demonstrate how changes in deposition conditions can dramatically influence the functional properties of an interface, even within the same material system. The energy band alignment at the heterointerface between Cu2O and ZnO was studied using photoelectron spectroscopy with stepwise deposition of ZnO onto Cu2O and vice versa. A large variation of energy band alignment depending on the deposition conditions of the substrate and the film is observed, with valence band offsets in the range ΔEVB = 1.45-2.7 eV. The variation of band alignment is accompanied by the occurrence or absence of band bending in either material. It can therefore be ascribed to a pinning of the Fermi level in ZnO and Cu2O, which can be traced back to oxygen vacancies in ZnO and to metallic precipitates in Cu2O. The intrinsic valence band offset for the interface, which is not modified by Fermi level pinning, is derived as ΔEVB ≈ 1.5 eV, being favorable for solar cell applications.

High-throughput computational and experimental techniques have been used in the past to accelerate the discovery of new promising solar cell materials. An important part of the development of novel thin film solar cell technologies, that is still considered a bottleneck for both theory and experiment, is the search for alternative interfacial contact (buffer) layers. The research and development of contact materials is difficult due to the inherent complexity that arises from its interactions at the interface with the absorber. A promising alternative to the commonly used CdS buffer layer in thin film solar cells that contain absorbers with lower electron affinity can be found in β-In2S3. However, the synthesis conditions for the sputter deposition of this material are not well-established. Here, In2S3 is investigated as a solar cell contact material utilizing a high-throughput combinatorial screening of the temperature-flux parameter space, followed by a number of spatially resolved characterization techniques. It is demonstrated that, by tuning the sulfur partial pressure, phase pure β-In2S3 could be deposited using a broad range of substrate temperatures between 500 °C and ambient temperature. Combinatorial photovoltaic device libraries with Al/ZnO/In2S3/Cu2ZnSnS4/Mo/SiO2 structure were built at optimal processing conditions to investigate the feasibility of the sputtered In2S3 buffer layers and of an accelerated optimization of the device structure. The performance of the resulting In2S3/Cu2ZnSnS4 photovoltaic devices is on par with CdS/Cu2ZnSnS4 reference solar cells with similar values for short circuit currents and open circuit voltages, despite the overall quite low efficiency of the devices (∼2%). Overall, these results demonstrate how a high-throughput experimental approach can be used to accelerate the development of contact materials and facilitate the optimization of thin film solar cell devices.