Search for: All records

Policies aiding biofuels have supported farm income and rural communities but have also put pressure on food security with questionable benefits related to carbon emissions. Photovoltaics (PV) are poised to become central to the overall energy decarbonization strategy, but because of land requirements they are likely to be developed on farmland, reigniting concerns related to food security. In this work, we study strategies for co-producing food and energy from corn croplands. We find that while traditional PV displaces crops, they can harvest orders of magnitude more energy per unit of land than biofuels. Additionally, systems with elevated PV panels (called PV Aglectric, Agrivoltaics, or Agrophotovoltaics) that allow for crop production underneath them can increase energy production and reduce carbon emissions with minimal impact on crop production. This technology can ease the trade-off between farm income, energy production, crop production, and energy decarbonization. Adoption of PV Aglectric systems may be hindered by high capital costs, but this barrier could be overcome with policy support, especially when crop prices are highly volatile. 

Thin film photovoltaics are a key part of both current and future solar energy technologies and have been heavily reliant on metal chalcogenide semiconductors as the absorber layer. Developing solution processing methods to deposit metal chalcogenide semiconductors offers the promise of low-cost and high-throughput fabrication of thin film photovoltaics. In this review article we lay out the key chemistry and engineering that has propelled research on solution processing of metal chalcogenide semiconductors, focusing on Cu(In,Ga)(S,Se)2 as a model system. Further, we expand on how this methodology can be extended to other emerging metal chalcogenide materials like Cu2ZnSn(S,Se)4, copper pnictogen sulfides, and chalcogenide perovskites. Finally, we discuss future opportunities in this field of research, both considering fundamental and applied perspectives. Overall, this review can serve as a roadmap to researchers tackling challenges in solution processed metal chalcogenides to better accelerate progress on thin films photovoltaics and other semiconductor applications. 

Tolerance factor analysis has been widely used to predict suitable compositions for oxide and halide perovskites. However, in the case of the emerging chalcogenide perovskites, the predictions from the tolerance factor have failed to align with experimental observations. In this work, we reconsider how tolerance factor is being applied, specifically adjusting for the effect of increased covalency of bonding on the ionic radii. Further, we propose a series of screening steps based on the octahedral factor, tolerance factor, and electronegativity difference to better predict the formation of sulfide perovskites. 

Oxide perovskites would provide a convenient precursor for the synthesis of chalcogenide perovskites. However, the stability of oxide perovskites means that there is no driving force for sulfurization or selenization with conventional chalcogen sources. In this work, we show that sulfurization and selenization of highly stable early transition metal oxides are possible by heating in the presence of HfH2 and S or Se, thereby creating HfS3 or HfSe3 as an oxygen sink and producing an oxygen shuttle in the form of H2O/H2S or H2O/H2Se. The conversion of ZrO2 into ZrS3 or ZrSe3 is supported with thermodynamic calculations and demonstrated experimentally as a proof-of-concept. Subsequently, we demonstrate that BaZrO3 can be converted to BaZrS3 at 575 °C, several hundred degrees below previous methods relying on conventional sulfur sources. 

Synthesis of homoleptic zirconium and hafnium dithiocarbamate via carbon disulfide insertion into zirconium and hafnium amides were investigated for their utility as soluble molecular precursors for chalcogenide perovskites and binary metal sulfides. Treating M(NEtR)4 (M= Zr, Hf and R= Me, Et) with CS2 resulted in quantitative yields of homoleptic Group IV dithiocarbamates. Zr(2-S2CNMeEt) (1), Zr(2-S2CNEt2)4 (2), and Hf(2-S2CNEt2)4 (4), a rare example of a crystal of a homoleptic hafnium CS2 inserted amide species, were characterized. A computational analysis confirmed assignments for IR spectroscopy. To exemplify the utility of the Group IV dithiocarbamates, a solution-phase nanoparticle synthesis was performed to obtain ZrS3 via the thermal decomposition of Zr(S2CNMeEt)4. 

In recent years, a growing interest in the development of new energy harvesting technologies based on earth-abundant, environmentally-friendly semiconductors, has led to the re-discovery of hitherto overlooked materials. Among them, Ag-based chalcohalides stand out for their abundancy and low-toxicity, as well as the crystal structure analogous to perovskite, albeit with cations in place of anions and vice-versa (i.e. anti-perovskite). Until now, inorganic anti-perovskites have generally been studied as solid-state electrolytes. Indeed, Ag3SI was identified in the 1960s as a superionic conductor. On the other hand, theorical calculations have demonstrated bandgaps in the visible range, suggesting that they could be suitable for PV applications. However, there is little published information on their potential as energy harvesting materials and so far, thin films have been prepared by solid-state reactions or physical vapor deposition techniques at high temperature and/or vacuum conditions, which limits their commercial viability owing to costly, non-scalable processes. In this work, we present a new procedure to synthesize Ag-based chalcohalides by a low-temperature solution-based methodology, using an thiol-amine reactive solvent system to dissolve Ag2S and AgX (X = Br, I) precursors, followed by spin coating deposition to obtain polycrystalline films. Through this process, it has been possible to synthesize Ag3S(IxBr1−x) (x = 0–1) films for the first time, which have been characterized, demonstrating the formation of the anti-perovskite phase and a linear correlation between structural parameters and composition. Optical characterization shows bandgap ranging from 0.9 eV (Ag3SI) to 1.0 eV (Ag3SBr), with a bowing effect for the intermediate solid solutions. First solar cells prototypes demonstrate photo-response and promising electrical characteristics. 

The solution-processing of metal chalcogenides offers a promising route to improve the manufacturing of semiconductor devices. The amine–thiol solvent system has been deemed an “alkahest” for its ability to dissolve a wide range of metals and metal chalcogenides. Therefore, it enables convenient synthesis of metal sulfides. However, in the literature there are limited reports of analogous selenium-based “alkahest” chemistry. Here we show that solutions containing n-alkylammonium polyselenides can dissolve a wide range of metals and metal compounds through the formation of soluble metal polyselenides. These metal polyselenides can subsequently be utilized as precursors for the synthesis of a wide range of binary and multinary metal selenide thin films and nanoparticles, including Cu(In,Ga)Se2, Cu2ZnSnSe4, and Ag2ZnSnSe4.