A Simple Aqueous Precursor Solution Processing of Earth-Abundant Cu₂SnS₃ Absorbers for Thin-Film Solar Cells

Abstract

A simple and eco-friendly method of solution processing of Cu2SnS3 (CTS) absorbers using an aqueous precursor solution is presented. The precursor solution was prepared by mixing metal salts into a mixture of water and ethanol (5:1) with monoethanolamine as an additive at room temperature. Nearly carbon-free CTS films were formed by multispin coating the precursor solution and heat treating in air followed by rapid thermal annealing in S vapor atmosphere at various temperatures. Exploring the role of the annealing temperature in the phase, composition, and morphological evolution is essential for obtaining highly efficient CTS-based thin film solar cells (TFSCs). Investigations of CTS absorber layers annealed at various temperatures revealed that the annealing temperature plays an important role in further improving device properties and efficiency. A substantial improvement in device efficiency occurred only at the critical annealing temperature, which produces a compact and void-free microstructure with large grains and high crystallinity as a pure-phase absorber layer. Finally, at an annealing temperature of 600 °C, the CTS thin film exhibited structural, compositional, and microstructural isotropy by yielding a reproducible power conversion efficiency of 1.80%. Interestingly, CTS TFSCs exhibited good stability when stored in an air atmosphere without encapsulation at room temperature for 3 months, whereas the performance degraded slightly when subjected to accelerated aging at 80 °C for 100 h under normal laboratory conditions.

8% Efficiency Cu2ZnSn(S,Se)4 (CZTSSe) Thin Film Solar Cells on Flexible and Lightweight Molybdenum Foil Substrates

“…The maximum EQE was found to be about 80% at 540 nm in CZTSSe TFSCs annealed at 520 °C. The lower EQE values in all CZTSSe TFSCs at higher wavelengths can be attributed to the insufficient collection of generated charge-carriers as a result of short minority carrier lifetimes. , We also compared J sc values obtained from the J – V curves recorded under a 100 mW/cm 2 solar simulator with the estimated J sc value by integrated the EQE curves (Table ). The energy gap ( E g ) values of the CZTSSe thin films were calculated from the linear extrapolation plot of ℏνln­(1–EQE) versus (ℏν), which were found to be 1.12, 1.13, 1.11, and 1.18 eV for CZTSSe thin films annealed at 480, 500, 520, and 540 °C, respectively (Figure c).…”

Colloidal Wurtzite Cu2SnS3 (CTS) Nanocrystals and Their Applications in Solar Cells

“…The S vapor pressures inside the graphite box were maintained at 150, 350, 550, and 750 Torr using 0.0047, 0.0109, 0.0171, and 0.0233 g of solid S powder, respectively. The resulting films were processed into solar cell devices following standard procedures, including chemical bath deposition of CdS (∼65 nm), radio frequency (RF) sputtering of i-ZnO (∼75 nm) and Al-ZnO (AZO) (∼500 nm), and direct current (DC) sputtering of a patterned Al grid as the top electrode . The final devices (2.5 cm × 2.5 cm) were mechanically scribed into cells with an active area of 0.30 cm 2 .…”

“…The resulting films were processed into solar cell devices following standard procedures, including chemical bath deposition of CdS (∼65 nm), radio frequency (RF) sputtering of i-ZnO (∼75 nm) and Al-ZnO (AZO) (∼500 nm), and direct current (DC) sputtering of a patterned Al grid as the top electrode. 25 The final devices (2.5 cm × 2.5 cm) were mechanically scribed into cells with an active area of 0.30 cm 2 . The details of the synthetic procedure, NC purification, characterization, ink formulation, annealing conditions and device fabrication are provided in the Supporting Information.…”

Aqueous-Solution-Processed Cu2ZnSn(S,Se)4 Thin-Film Solar Cells via an Improved Successive Ion-Layer-Adsorption–Reaction Sequence

“…1,2 Scalable solution-processing methods of these earth-abundant compounds have attracted increasing attention owing to their low cost, high-throughput capability, and compatibility with a variety of substrates. 3,4 A state-of-the-art power conversion efficiency (PCE) of 12.7% has been achieved for a CZTSSe TFSC using hydrazine-based solution processing employing a double In 2 S 3 /CdS emitter. 5 However, despite the record efficiency of the state-of-the-art CZTSSe TFSC, hydrazine is highly toxic and flammable, which requires various handling precautions during precursor solution and thin-film preparation, limiting the use of this solution-processing technique to grow CZTSSe absorbers in a viable manner for commercialization.…”