In this work, we present an investigation of the junction interface roughness effect on the open circuit voltage, Voc for thin film heterojunction photovoltaics. The roughness effect is studied for self‐affine rough interfaces, which are described in Fourier space by the correlation model ∼σ2ξ2(1+aq2ξ2)−1−H. σ, ξ, and H denote, respectively, the rms roughness, the in‐plane roughness correlation length, and the interface irregularity exponent (0<H<1). The roughness effect becomes significant for small H (<0.5), and for large long‐wavelength roughness of typical values σ/ξ∼0.1. The junction interface roughness may yield a contribution to Voc even up to 10%. Comparison of the results is performed with predictions in real heterojunctions, e.g., CuxS/(Zn)CdS.
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