Experimental Characterization of Sol–Gel Spin-Coated Al-Doped ZnO/CdTe Heterojunction Thin Films
Abstract
Al-doped zinc oxide (AZO) has attracted sustained interest as a low-cost, earth-abundant n-type transparent conducting oxide for solution-processed heterojunction photovoltaics. In the present work, undoped ZnO and AZO (2 mol% Al/Zn) thin films were deposited on p-CdTe by a sol–gel spin-coating route and examined as direct, CdS-free ZnO(AZO)/CdTe heterojunctions – a configuration for which experimental reports remain scarce. The structural, optical, electrical, and morphological responses were investigated by XRD, UV–Vis absorbance spectroscopy with first-derivative band-edge analysis, dark and illuminated J–V measurements with Cheung–Cheung diode-parameter extraction, and SEM. XRD confirmed the coexistence of zinc-blende CdTe and c-axis-oriented wurtzite ZnO, with Scherrer crystallite sizes of 27 ± 5 nm. The derivative absorbance maximum shifted from 3.31 eV (ZnO) to 3.33 eV (AZO). Under illumination, the AZO/CdTe device yielded Jsc ≈ 4.2mA·cm-2, Voc ≈ 0.43V, with n ≈ 3.1, Rs ≈ 28 Ω·cm2, Rsh ≈ 310 Ω·cm2, FF ≈ 27%, η ≈ 0.49%. SEM revealed a pinhole-free polycrystalline AZO overlayer (30–80 nm grains). The results establish a baseline characterization of buffer-free, solution-processed AZO/CdTe heterojunctions.
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