A Cd-diffusion strategy to prepare Cu2CdSnS4 thin films for solar cells

We present a Cd-diffusion strategy to fabricate large-grained, phase-pure Cu 2 CdSnS 4 absorber films by sulfurizing a solution-processed bi-layer CdS/Cu 2 SnS 3 films. The key novelty lies in using Cd diffusion from a thin underlying CdS layer to uniformly convert a Cu 2 SnS 3 layers into Cu 2 CdSnS 4 , successfully eliminating the small-grained bottom layer that typically plagues solution-processed kesterite/stannite films. We demonstrate that the phase transformation to pure Cu 2 CdSnS 4 is governed by the final Cd content in the film matrix, not by the Cd diffusion length. Optimized films, obtained at a sulfurization temperature of 550 °C, exhibit ideal optoelectronic properties with a band gap of ∼1.40 eV and a high absorption coefficient (>10 5  cm −1 ). Solar cells in a FTO/TiO 2 /Cu 2 CdSnS 4 /P3HT/MoO 3 /Ag configuration achieve a power conversion efficiency of 3.81 %, attributed to the high-quality, large-grained Cu 2 CdSnS 4 absorber. This work provides a promising pathway for developing efficient thin-film solar cells with homogeneous morphology.