The adsorption 2-anthroic acid on titania has been shown to result in an interfacial charge transfer band, which makes this a promising interface for dye-sensitized solar cells with direct injection. Here, we model the adsorption of 2-anthroic acid on a TiO2 nanocluster exhibiting a (101)-like interface and compute light absorption properties of this system using for the first time a hybrid functional. The band alignment and the formation of interfacial charge transfer bands proposed in previous experimental and lower-level computational works are confirmed.

Tin sulfide has emerged as a promising solar absorber among the IV-VI binary compound which is earth-abundant and non-toxic. This research provides a new perspective on synthesis of photosensitive monophasic SnS films by organic chemical vapor sulfurization of Sn thin film. S-radicals formed by closed space pyrolysis of di-tert-butyl disulfide (TBDS) diffusively react with Sn to produce SnS film. SnS being an amphoteric semiconductor converts to n-type by trivalent Sb and Bi dopants. The organic vapor sulfurization method described in this research facilitates single-step synthesis of buried junction structures and thus SnS solar cells in a p-n homojunction or p-i-n structures. In this work, vacuum evaporated Sn thin film with a thickness of 100 nm, was converted to SnS by sulfurization under 100 sccm flow of TBDS vapor preheated to 100°C and structural phase evolution and film growth kinetics were investigated for sulfurization at 200°C, 300°C and 400°C for a periods 90 min. X-ray diffraction studies establish single phase highly crystalline film in orthorhombic crystal structure forms at 200°C. Raman scattering results confirm SnS formation with the identification of 2Ag, 2B2g optical phonons modes. Optical bandgap studies confirm a low energy 1.1-1.4 eV indirect bandgap and a strong absorption threshold between 1.4 to 1.6 eV direct band gap depending on the sulfurization conditions correlating with intrinsic defects and phase structure of the film.

The solar absorptance property of W/WAlN/WAlON/Al2O3-based coatings, deposited by DC/RF magnetron sputtering on stainless steel substrate was studied by measuring the reflectance spectra in the wavelength range of 250 - 2500 nm. The effect of thermal annealing on the optical properties of the solar selective absorber coatings was investigated. Annealing the coatings at 450°C for 150 hrs in air did not show any significant change in the spectral properties of the absorber coating indicating the excellent thermal stability of the coating. The W layer acts as infrared reflective layer and diffusion barrier on stainless steel substrate. The top Al2O3 layer serves as dense shield to protect the under layers from oxidation in air. In summary, the present study indicates the potential application of W/WAlN/WAlON/Al2O3-based selective coatings in high temperature photo thermal conversion systems.

To reduce the amount of chalcogen needed in the post-annealing process, we demonstrate significantly increased sulfur incorporation into pure sulfide CZTS films achieved by increasing the thiourea content of DMSO-based precursor solution. The increase of sulfur content was confirmed by thermogravimetric analyses (TGA). To understand how the elemental distribution across the CZTS layer is affected by extra thiourea, a systematic compositional study was carried out using X-ray photoelectron spectroscopy (XPS). XPS depth profiling reveals increased sulfur incorporation in the final CZTS films when more thiourea is added to the solution. The grain size was reduced slightly with increased sulfur content and the surface morphology was changed significantly. The effect on the surface of the CZTS film has been investigated using scanning electron microscopy (SEM), Raman spectroscopy, and XPS. External-quantum-efficiency (EQE) measurements with an electrolyte contact were used to investigate the optoelectronic properties of the deposited CZTS films.

WSe2 films have been fabricated using a low-temperature, two-step method involving the reaction of W(CO)6 and elemental selenium in refluxing (110 °C) toluene to form a nanocrystalline precursor consisting of amorphous tungsten and trigonal crystalline selenium. Drop cast or airbrush-deposited films of this precursor were annealed in an argon atmosphere using a two-step temperature ramp (250 °C for 15 min followed by 550 °C for 30 min). Raman and x-ray diffraction (XRD) characterization as well as the measured bandgaps of the resulting films are consistent with (002)-oriented WSe2 and are compared to the characterization of films produced via selenization of sputtered tungsten films in closed quartz tubes at 875 °C.

The U.S. Department of Energy (DOE)’s SunShot Initiative is a collaborative national effort to reduce the price of solar energy to 6¢/kWh without subsidy for utility scale installations by 2020. Thin-film photovoltaics offer a promising path to reach this goal. Analysis of the levelized cost of energy (LCOE) from photovoltaics (PV) highlights the dependence on the module and system efficiency and lifetime in addition to module price. Here we summarize challenges and opportunities for CdTe and CIGS PV research and show that a substantial effort is still needed in areas such as device design and material improvement to reach higher efficiency and reliability connected with low-cost and robust module-scale implementation. We also discuss how SunShot Initiative funding is addressing key research areas in CdTe and CIGS PV and show how recent progress in SunShot projects is guiding funding priorities in thin-film PV research.

Polycrystalline <100 nm thin CdS films deposited by the chemical bath deposition (CBD) method are used as n-type window layer in high efficiency heterojunction CuInSe2, Cu2ZnSnS4, and CdTe solar cells. The major shortcoming of the CdS films is its stability and high sub-bandgap absorption. In the present work, an alternative window layer for the heterojunction solar cells based on cadmium oxysulfide Cd(S,O) thin films formed by the CBD method is described. The ∼100 nm thin Cd(S,O) films formed by co-deposition of CdS with CdO show high >85% optical transmittance over 550-1000 nm region compared to 70% transmission in CdS films. Cd(S,O) film formed with highly conformal coverage showed as direct optical band gap of 2.19-2.09 eV depending on the CdO fraction in the film. The CBD growth of CdS is via controlled release of S2- and Cd2+ ions in an alkaline medium through complexing to prevent CdS or Cd(OH)2 as colloids in the solution phase. In the present method, by altering the substrate conditions we carried out controlled Cd(OH)2 deprotonation reaction to form CdO over the substrate concurrently with CdS to deposit Cd(S,O) films. These films are polycrystalline having wurtzite structure identified by (002), (110) and (112) x-ray diffractions. Formation of Cd(S,O) phase is confirmed by Raman spectra which besides the characteristic CdS 1LO and 2LO modes at 300 and 600 cm-1, also showed Raman lines from CdO at 1094 cm-1 and 943 cm-1 assigned as overtone of 2LO phonon modes at the L or Γ points of the Brillouin zone of CdO.