Yaroslav E. Romanyuk

Bio: Yaroslav E. Romanyuk is an academic researcher from Swiss Federal Laboratories for Materials Science and Technology. The author has contributed to research in topics: Thin film & Copper indium gallium selenide solar cells. The author has an hindex of 34, co-authored 146 publications receiving 4338 citations. Previous affiliations of Yaroslav E. Romanyuk include École Polytechnique Fédérale de Lausanne & Lawrence Berkeley National Laboratory.

Highly efficient Cu(In,Ga)Se2 solar cells grown on flexible polymer films

Abstract: Solar cells based on polycrystalline Cu(In,Ga)Se(2) absorber layers have yielded the highest conversion efficiency among all thin-film technologies, and the use of flexible polymer films as substrates offers several advantages in lowering manufacturing costs. However, given that conversion efficiency is crucial for cost-competitiveness, it is necessary to develop devices on flexible substrates that perform as well as those obtained on rigid substrates. Such comparable performance has not previously been achieved, primarily because polymer films require much lower substrate temperatures during absorber deposition, generally resulting in much lower efficiencies. Here we identify a strong composition gradient in the absorber layer as the main reason for inferior performance and show that, by adjusting it appropriately, very high efficiencies can be obtained. This implies that future manufacturing of highly efficient flexible solar cells could lower the cost of solar electricity and thus become a significant branch of the photovoltaic industry.

Sodium Assisted Sintering of Chalcogenides and Its Application to Solution Processed Cu2ZnSn(S,Se)4 Thin Film Solar Cells

Abstract: Cu2ZnSn(S,Se)4 thin layers processed from solution-deposited earth-abundant precursors emerge as absorber materials for low-cost thin film solar cells. A frequently observed drawback of the chemical solution processing—poor crystallinity of the chalcogenide absorber—can be overcome by employing a sodium-containing reactive agent. We demonstrate a massive improvement in grain growth in the presence of sodium. It enhances the surface chemisorption of selenium molecules and can promote the formation of liquid Na2Sex phases during reactive annealing of the precursor. The sodium is also incorporated into the semiconductor absorber and significantly modifies its electronic properties. By adjusting the sodium precursor quantity, it is possible to tune doping levels and gradients to maximize the collection of photogenerated carriers in thin film Cu2ZnSn(S,Se)4 solar cells. The presented approach can be extended to other solution-processed metal chalcogenides to enhance their structural and electronic properties, ...

Highly Transparent and Conductive ZnO: Al thin films from a low temperature aqueous solution approach

Abstract: A solution deposition approach for high-performance aluminum-doped zinc oxide (AZO) thin films (visible transparency > 90% and sheet resistance down to 25 Ω/sq) with process temperatures not exceeding 85 °C is presented. This allows the non-vacuum deposition of AZO on temperature sensitive substrates such as polymer films for flexible and transparent electronics, or inorganic and organic thin film photovoltaics.

Yb-doped KY(WO4)2 planar waveguide laser

Abstract: High-quality monoclinic $KY(WO_{4})_{2}$ optical waveguides were grown by liquid-phase epitaxy, and laser operation of an Yb-doped $KY(WO_{4})_{2}$ waveguide was demonstrated for the first time to our knowledge. Continuous-wave laser emission near 1 μm was achieved with both surface and buried planar waveguides. An output power of 290 mW was obtained in the fundamental mode and the slope efficiency was above 80%.

Low-temperature processed meso-superstructured to thin-film perovskite solar cells

Abstract: We have reduced the processing temperature of the bulk absorber layer in CH3NH3PbI3−xClx perovskite solar cells from 500 to <150 °C and achieved power conversion efficiencies up to 12.3%. Remarkably, we find that devices with planar thin-film architecture, where the ambipolar perovskite transports both holes and electrons, convert the absorbed photons into collected charge with close to 100% efficiency.

Ultrathin and lightweight organic solar cells with high flexibility

Abstract: Organic solar cells are promising for technological applications, as they are lightweight and mechanically robust. This study presents flexible organic solar cells that are less than 2 μm thick, have very low specific weight and maintain their photovoltaic performance under repeated mechanical deformation.

Potassium-induced surface modification of Cu(In,Ga)Se2 thin films for high-efficiency solar cells

Abstract: Thin-film photovoltaic devices based on chalcopyrite Cu(In,Ga)Se2 (CIGS) absorber layers show excellent light-to-power conversion efficiencies exceeding 20%. This high performance level requires a small amount of alkaline metals incorporated into the CIGS layer, naturally provided by soda lime glass substrates used for processing of champion devices. The use of flexible substrates requires distinct incorporation of the alkaline metals, and so far mainly Na was believed to be the most favourable element, whereas other alkaline metals have resulted in significantly inferior device performance. Here we present a new sequential post-deposition treatment of the CIGS layer with sodium and potassium fluoride that enables fabrication of flexible photovoltaic devices with a remarkable conversion efficiency due to modified interface properties and mitigation of optical losses in the CdS buffer layer. The described treatment leads to a significant depletion of Cu and Ga concentrations in the CIGS near-surface region and enables a significant thickness reduction of the CdS buffer layer without the commonly observed losses in photovoltaic parameters. Ion exchange processes, well known in other research areas, are proposed as underlying mechanisms responsible for the changes in chemical composition of the deposited CIGS layer and interface properties of the heterojunction.