Compound surface textures for enhanced near-infrared light havesting of crystallin silicon solar cells

As silicon photovoltaics evolve towards thin-wafer technologies, efficient optical absorption for the near-infrared wavelengths has become particularly challenging. In this work, we present a solution that employs combined micro- and nano-scale surface textures to increase light harvesting in the near-infrared for crystalline silicon photovoltaics, and discuss the associated antireflection and scattering mechanisms. The surface textures are achieved by uniformly depositing a layer of indium-tin-oxide nanowhiskers on micro-grooved silicon substrates using electron-beam evaporation. The nanowhiskers facilitate optical transmission in the near-infrared by functioning as impedance matching layers with effective refractive indices gradually varying from 1 to 1.3. Materials with such unique refractive index characteristics are not readily available in nature. Compared to the reflectance of the conventional silicon solar cell, the combined textures structure provided broadband high absorption, especially in the near infrared region. As a result, the solar cell with combined textures achieves over 90% external quantum efficiencies for a broad wavelength range of 460 to 980 nm, which is crucial to the development of advanced thin-substrate silicon solar cells. Due to the high photocurrent contributed to the performance, the compound textured solar cell increased the 1.1% absolute power conversion efficiency, from 16.1% to 17.2%.