High‐performance Cu2ZnSnS4 photovoltaic devices are demonstrated using electrodeposition of metal stacks and annealing of a CuZnSn precursor in a sulfur atmosphere. A champion electroplated Cu2ZnSnS4 solar cell achieves a power conversion efficiency of 7.3%, which is a record efficiency for electrodeposited Cu2ZnSnS4 solar devices. The device performance points to electrodeposition and annealing as a low‐cost and viable approach to earth‐abundant solar cell fabrication.

Electrochemical deposition of metals onto foreign substrates usually occurs through Volmer–Weber island growth. The mechanism of island nucleation and growth dictates the shape, orientation and number density of islands, and ultimately, the structure and properties of thin films. With increasing emphasis on deposition of ultrathin films and nanostructures, it is critically important to understand the kinetics of nucleation and growth. Here we provide a comprehensive review of island growth in electrodeposition and summarize methods for mechanistic analysis in both the kinetic and diffusion limited regimes.

High performance Cu 2 ZnSnSe 4 (CZTSe) photovoltaic materials were synthesized by electrodeposition of metal stack precursors followed by selenization. A champion solar cell with 7.0% efficiency is demonstrated. This is the highest efficiency among all of the CZTSe solar cells prepared from electrodeposited metallic precursors reported to-date. Device parameters are discussed from the perspective of material microstructure and composition in order to improve performance. In addition, a high performance electrodeposited CZTS (S only) solar cell was demonstrated and its device characteristics were compared against the CZTSe (Se only) cell. Using secondary ion mass spectrometry for the analysis of the chemical composition of the absorber layer, a higher concentration of oxygen in the electrodeposited absorber is thought to be the root cause of the lower performance of the electrodeposited CZTS or CZTSe solar cells with respect to a solar cell fabricated by evaporation. The grain boundary areas of Sn-rich composition are thought to be responsible for the lower shunt resistance commonly observed in CZTSe devices. We measured the longest minority carrier lifetime of 18 ns among all reported kesterite devices. This work builds a good baseline for obtaining higher efficiency earth-abundant solar cells, while it highlights electrodepositon as a low cost and feasible method for earth-abundant thin film solar cell fabrication.

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Ruthenium is an alternative liner material for copper metallization. We report on the nucleation and growth of copper on ruthenium in acidified copper sulfate solution and explore the influence of the PEG-Cl-SPS additive system. We show that the physical vapor deposition ruthenium has an oxide layer approximately 1 nm thick. The additives and copper concentration have a relatively small influence on island density but a significant influence on the island morphology. Without additives, both randomly oriented hemispherical islands and disk-shaped islands with a ͑111͒ orientation are observed. The distribution of islands is dependent on potential. In the presence of additives, the islands are irregular in shape due to renucleation that becomes more pronounced at higher concentrations and lower overpotentials. Analysis of the island size distributions implies that nucleation is fast in comparison to growth. The island density is exponentially dependent on potential increasing from 10 7 cm −2 at low overpotentials to almost 10 11 cm −2 at larger overpotentials. The distribution of islands at the surface is shown to be consistent with complete spatial randomness.

Interactions between the cathodic and anodic processes during electroless Cu deposition using glyoxylic acid reducing agent are studied. It is shown that application of the mixed potential theory by decoupling the anodic and cathodic processes leads to erroneous predictions of the electroless deposition rate and the surface mixed potential observed in this electroless system. Chronoamperometry under various conditions of bath composition, electrode surface preparation and applied potential provides evidence for an autocatalytic mechanism in the glyoxylic acid based electroless Cu system. Specifically, it is observed that the electroless Cu surface accelerates the glyoxylic acid oxidation and the glyoxylic acid in turn enhances the cupric-ion reduction leading to a positive feedback loop. The autocatalysis explains shortcomings in the simplistic application of the mixed potential theory to the decoupled partial reactions, and suggests a more complex reaction mechanism in which the partial reactions are coupled.

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Nucleation and growth during bulk electrodeposition is studied using kinetic Monte Carlo (KMC) simulations. Ion transport in solution is modeled using Brownian dynamics, and the kinetics of nucleation and growth are dependent on the probabilities of metal-on-substrate and metal-on-metal deposition. Using this approach, we make no assumptions about the nucleation rate, island density, or island distribution. The influence of the attachment probabilities and concentration on the time-dependent island density and current transients is reported. Various models have been assessed by recovering the nucleation rate and island density from the current-time transients.