Requirements for TCO Substrate in Si-based Thin Film Solar Cells -Toward Tandem

Abstract

Newly developed SnO2:F films having “double–texture (W-texture)” were evaluated in terms of optical and electrical properties and compared with Asahi type-U substrate. “W-textured” transparent conductive oxide (TCO) film was composed of a combination of 300-500nm large hills and small pyramidal texture covering them. “W-textured” TCO could show a large haze value exceeding 80% even at 800nm. Microcrystalline Si (μc-Si:H) thin film solar cells were fabricated on these TCOs and characterized. The result showed that a quantum efficiency of μc-Si:H solar cells was improved with “W-textured” TCOs significantly in longer wavelength region.

Light Trapping effects in Thin Film Silicon Solar Cells

“…The insertion of a thin SiOx layer using the same conditions as the SOIR layer, but only 5 nm thick, can effectively break the local epitaxy and force the ZnO to nucleate new grains. The right panel of Figure 8 shows that the result is a double structure that resembles to some extent the recently developed Asahi W structure [24]. Table 1.…”

UV micro-imprint patterning for tunable light trapping in p-i-n thin-film silicon solar cells

“…From the results reported by recent investigations related to light trapping for a broad wavelength range, it can be concluded that TCO films should be fabricated with multiscale features [10][11][12][13]. Herein, craters with larger feature sizes have been fabricated on top of glass treated with UV lithography.…”

“…Hence, a textured substrate with a broad texture-size distribution that assures scattering for the entire wavelength range of the solar spectrum is the best choice for thin film solar cells. Recently, some novel methods were developed pointing in this direction, among which one can highlight the fabrication of films with two characteristic texture sizes, such as the double-texture (W-texture) SnO 2 :F films fabricated by Asahi [10], and greater cauliflower-like multitextured BZO made by metal organic chemical vapor deposition (MOCVD) preceded by glass-substrate etching [11]. Furthermore, multi-scale transparent electrodes have been proposed by combining the versatility of nanoimprint lithography, the unusually high carrier mobility of hydrogenated indium oxide, and the unequaled light-scattering properties of self-textured zinc oxide [12] as well as an effective light trapping technique in thin film silicon solar cells based on a multi-step process to make aluminumdoped ZnO (AZO) films with a wide texture-size distribution [13].…”

New method to measure whole-wavelength transmittance of TCO substrates for thin-film silicon solar cells

“…In order to improve light trapping, many researchers have studied to increase haze ratio by adjusting deposition conditions of atmosphere pressure chemical vapor deposition (APCVD) [3,4], applying reactive ion etched glass substrates [5e8] (so-called "W-textured TCO"), applying photolithography etched substrates [9], and applying nanoimprint plastic mold [10e15]. To measure the transmittance and reflectance of TCO substrates with high haze, an immersion (IM) method is widely used [16e18].…”