Optically Rough and Physically Flat Transparent Conductive Substrates with Strong Far-Field Scattering

Optically rough and physically flat transparent conductive (OR-PF) substrates facilitate the performance improvement of optoelectronic devices and functional glasses via simultaneously enabling high-quality growth of functional layers and effective light management. This paper studies the effect of the interface morphology of the hole array pattern (HAP) and the pillar array pattern (PAP) on the far-field scattering properties of OR-PF substrates fabricated by spin-coating Al-doped ZnO (AZO) on nanoimprint-patterned glasses for improving the performance of superstrate-type thin-film solar cells. Theoretical calculation based on bidirectional scattering distribution function predicts that HAP with a period of 1.5 μm and a diameter of 1.3 μm [HAP(P1.5D1.3)] and the PAP(P1.0D0.5) interface morphology have a haze ratio in transmission (H_T) of around 64% and a scatter angle of larger than 34°. The fabricated AZO/HAP(P1.5D1.3) and AZO/PAP(P1.0D0.5) show a flat surface with a σ_rms of less than 9 nm, a high visible light transmittance of over 86%, a sheet resistance of about 30 Ω/sq, and strong far-field scattering. In particular, AZO/PAP(P1.0D0.5) possesses an average H_T of over 11% at the wavelength range of 600-850 nm and an angular intensity distribution of over 1.5% at an azimuthal angle of around 55°, indicating stronger far-field scattering than the conventional pyramid-textured B-doped ZnO (BZO/F). Compared to the flat substrate, AZO/PAP generates an implied J_sc gain of 16.2% in a CH₃NH₃PbI₃ photoactive layer with a thickness of 300 nm under normal incidence at the wavelength range of 550-800 nm. For 60° incidence, AZO/PAP(P1.0D0.5) enables an implied J_sc gain of 2.3% with respect to BZO/F. As applied to the front electrode of CH₃NH₃PbI₃ thin-film solar cells, compared to BZO/F, AZO/PAP(P1.0D0.5) would enable a gain of up to 16.7 and 11.2% in photoelectric conversion efficiency for the 0 and 60° incidence, respectively.