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Suresh, Sunil

University of British Columbia

Renewable energy sources are necessary to enable persistent economic growth cleanly and sustainably. The sun is one such source irradiating Earth with 120,000 TW of power annually (both land and water), from which humans require only a small fraction of 15 TW globally. Multi-junction can utilize the solar spectrum more efficiently by reducing thermalization losses and can theoretically achieve efficiencies from 42% for a dual junction device under 1 Sun. Distinguished by a direct bandgap, and a large absorption coefficient, CuIn(S,Se)₂ absorber layers are of utmost importance for the growing field of printed solar cells. The widescale adoption of CuIn(S,Se)₂ thin film solar cells rely on device performance, operational stability, and production cost. Ink deposition routes for CuIn(S,Se)₂ absorbers have generated tremendous interest in the research community as an alternative to state-of-the-art vacuum-based deposition methods addressing challenges of low material usage, throughput, and film homogeneity. Herein a dimethylformamide and thiourea -based ink deposition route was explored to fabricate narrow bandgap (~1.0 eV) CuIn(S,Se)₂ films with Cu-poor, stoichiometric, and Cu-rich compositions for photovoltaic applications. Characterization of the Cu-rich absorber films using X-ray diffraction and scanning electron microscopy confirmed the partial removal of Cu₂₋ₓSe phase from the film surface, while electron backscatter diffraction measurements and depth-dependent energy-dispersive X-ray spectroscopy indicated remnant Cu₂₋ₓSe in the absorber layer bulk. Consequently, by carefully tailoring the ink and absorber film composition, active area efficiencies of 13.2% were obtained for devices with CuIn(S,Se)₂ absorber layers. Next, submicron thick CuIn(S,Se)₂ absorber films were fabricated using the developed ink-based route. Using submicron CuIn(S,Se)₂ absorber layers lowers the film fabrication costs, however, at the expense of lower power conversion efficiencies (due to rear surface recombination losses). To address the latter, an ultrathin Al₂O₃ film (~6 nm) with nanosized point openings between the rear contact and the CuIn(S,Se)₂ absorber layer was used to reduce the rear interface recombination losses. Active area solar cell efficiencies of 14.2%, and ~12.0% obtained by a 0.75 µm, and 0.55 µm film-based rear passivated device, respectively, which is the highest reported values for solution processed, low bandgap CuIn(S,Se)₂ solar cells with equivalent CuIn(S,Se)₂ film thicknesses.

Text

2024-11-02

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/86443

Mechanical Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/