Growth-Mode-Modulated Defects in Non-Hydrogenated a-Si Thin Films for Photothermal Conversion

Nanostructured Si exhibits superior photothermal performance and is a cost-effective solar absorbing material for solar evaporation, photothermal catalysis, and solar power systems. Defects are effective nonradiative recombination centers and are suppressed in amorphous silicon (a-Si) to benefit radiative recombination. In this research, a bottom-up approach to optimize the disordered and defective structure of non-hydrogenated a-Si by magnetron sputtering for photothermal conversion is proposed. The 2D mesoporous structure is developed in a-Si thin films under the growth scenario with reduced nucleation density. Local disorder and defects are analyzed based on the vibrational response of Si-Si bonds. Accompanied by narrowed bandgap (Eg) of 1.06 eV (Eu) and elongated Urbach tail of 0.49 eV, prominent short-range disorder and substantial amounts of dangling bonds contribute to enhanced solar absorption. Thereby, the full-spectrum absorptance above 92% can be realized with antireflection coatings of SiO2/Si3N4. The electron-phonon behavior revealed by resonance Raman scattering provides a comparative study on phonon production. Stronger electron-phonon coupling originated from the defective structure can be achieved at larger Eu. Provided with narrowed Eg and elongated Eu, local disorder and coordinative defects benefit both broadband absorption and thermal production, which can be introduced with controlled nucleation density and arrival rates. Coordinative defects in non-hydrogenated a-Si contribute to narrowed bandgaps and elongated band tails, benefiting broadband absorption and nonradiative recombination. Reduced nucleation density and increased arrival rates are responsible for prominent local disorder and defective structure of 2D mesoporous a-Si thin films, which indicate that enhanced photothermal conversion can be realized at Frank-van der Merwe growth modes.image (c) 2023 WILEY-VCH GmbH