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Silver nanowire (AgNW) networks are promising candidates to replace indium-tin-oxide (ITO) as transparent conductors. However, complicated treatments are often required to fuse crossed AgNWs to achieve low resistance and good substrate adhesion. In this work, we demonstrate a simple and effective solution method to achieve highly conductive AgNW composite films with excellent optical transparency and mechanical properties. These properties are achieved via sequentially applying TiO(2) sol-gel and PEDOT:PSS solution to treat the AgNW film. TiO(2) solution volume shrinkage and the capillary force induced by solvent evaporation result in tighter contact between crossed AgNWs and improved film conductivity. The PEDOT:PSS coating acts as a protecting layer to achieve strong adhesion. Organic photovoltaic devices based on the AgNW-TiO(2)-PEDOT:PSS transparent conductor have shown comparable performance to those based on commercial ITO substrates.

Understanding the electrically active defects in kesterite Cu2ZnSn(S,Se)4(CZTSSe) is critical for the continued development of solar cells based on this material, but challenging due to the complex nature of this polycrystalline multinary material. A comparative study of CZTSSe alloys with three different bandgaps, made by introducing different fractions of sulfur during the annealing process, is presented. Using admittance spectroscopy, drive level capacitance profiling, and capacitance‐voltage profiling, the dominant defect energy level present in the low sulfur content device is determined to be 0.134 eV above the valence band maximum, with a bulk defect density of 8 × 1014 cm−3, while the high sulfur content device shows a deeper defect energy level of 0.183 eV and a higher bulk defect density, 8.2 × 1015 cm−3. These findings are consistent with the current density–voltage characteristics of the resulting solar cells and their external quantum efficiency. It suggests that as the sulfur content increases, the bandgap of the absorber is enlarged, leading to an increasing open‐circuit voltage (Voc), that is accompanied by stronger recombination due to the higher defect density of the sulfur‐rich absorber. This is reflected in large Voc deficit and poor carrier collection of the high sulfur content device.

A novel solution-based approach is presented to process earth-abundant Cu(2)ZnSn(S,Se)(4) absorbers using fully dissolved CZTS precursors in which each of the elemental constituents intermix on a molecular scale. This method enables the low-temperature processing of chemically clean kesterite films with excellent homogeneity. The high performance of resulting optoelectronic devices represents a chance to extend the impact of CZTS into the next chapter of thin-film solar cells.

An effective defect passivation route has been demonstrated in the rapidly growing Cu2ZnSn(S,Se)4 (CZTSSe) solar cell device system by using Cu2ZnSnS4:Na (CZTS:Na) nanocrystals precursors. CZTS:Na nanocrystals are obtained by sequentially preparing CZTS nanocrystals and surface decorating of Na species, while retaining the kesterite CZTS phase. The exclusive surface presence of amorphous Na species is proved by X-ray photoluminescence spectrum and transmission electron microscopy. With Na-free glasses as the substrate, CZTS:Na nanocrystal-based solar cell device shows 50% enhancement of device performance (∼6%) than that of unpassivated CZTS nanocrystal-based device (∼4%). The enhanced electrical performance is closely related to the increased carrier concentration and elongated minority carrier lifetime, induced by defect passivation. Solution incorporation of extrinsic additives into the nanocrystals and the corresponding film enables a facile, quantitative, and versatile approach to tune the defect property of materials for future optoelectronic applications.

Earth abundant kesterite solar cells have achieved 7-10% cell efficiency mostly by processes that separate the film deposition and the annealing into two sequential steps. In contrast, co-evaporation onto a high-temperature substrate, demonstrating previous success in chalcopyrite (Cu(In,Ga)Se 2 ) solar cells, allows real-time composition control. Chalcopyrite research widely supports the model that Cu-rich growth conditions assist grain growth, and subsequently, the endpoint composition can be adjusted back to Cu-poor via monitoring the surface emissivity of the film. On the basis of the same intentions, the recent development of co-evaporated kesterite (Cu 2 ZnSnSe 4 ) adapts the concept and achieves 9.2% efficiency. To understand the effect of growth strategies, this study examines the phase evolution, grain morphology, and device performance in Cu-rich growth and other strategies (Zn-rich and close-to-stoichiometric). By characterizing films obtained from interrupted depositions and also interpreting the variation in surface emission during growths, this study found a subtle hindrance in the reaction of Cu x Se y and ZnSe possibly caused by the volatile nature of SnSe x . The hindrance explains why, distinctive from chalcopyrite, little difference in grain size is observed between kesterite films made by Cu-rich versus Zn-rich growth at these deposition rates. At last, a Zn-rich growth 9.1% device, certified by the National Renewable Energy Laboratory, is presented, which equals the performance of the previously-reported Cu-rich growth device. At the present stage, we believe the Cu-rich and Zn-rich growth share equal promise for the optimization of kesterite solar cells.

Atomic layer etching (ALE) is a multistep process used today in manufacturing for removing ultrathin layers of material. In this article, the authors report on ALE of Si, Ge, C, W, GaN, and SiO2 using a directional (anisotropic) plasma-enhanced approach. The authors analyze these systems by defining an “ALE synergy” parameter which quantifies the degree to which a process approaches the ideal ALE regime. This parameter is inspired by the ion-neutral synergy concept introduced in the 1979 paper by Coburn and Winters [J. Appl. Phys. 50, 5 (1979)]. ALE synergy is related to the energetics of underlying surface interactions and is understood in terms of energy criteria for the energy barriers involved in the reactions. Synergistic behavior is observed for all of the systems studied, with each exhibiting behavior unique to the reactant–material combination. By systematically studying atomic layer etching of a group of materials, the authors show that ALE synergy scales with the surface binding energy of the bulk material. This insight explains why some materials are more or less amenable to the directional ALE approach. They conclude that ALE is both simpler to understand than conventional plasma etch processing and is applicable to metals, semiconductors, and dielectrics.

The hydrazine-based deposition of Cu(In,Ga)(S,Se) 2 (CIGS) thin fi lms has attracted considerable attention in recent years due to its potential for the high-throughput production of photovoltaic devices based on this absorber material. This article provides an introduction as well as presenting a complete picture of the current status of hydrazine-based CIGS solar-cell fabrication, including the three major steps of this deposition process: dissolution of the precursor materials in hydrazine, deposition of a fi lm from the resulting precursor solution, and the completion and characterization of a photovoltaic device following absorber deposition. Recent discoveries are then discussed, regarding the dissolution chemistry of the relevant precursor complexes in hydrazine, which together represent the true foundation of this processing method. Recent studies on CIGS fi lm formation are then summarized, including the control and analysis of the crystalline phase, electronic bandgap, and fi lm morphology. Finally, the latest progress in high-performance device fabrication is highlighted, with a focus on optoelectronic characterization including current-voltage, junction capacitance, and minority carrier lifetime measurements. Finally, a discussion and future outlook is provided.