Impact of thermal processing route on the structural and photovoltaic properties of chloride-treated CdTe

Chloride activation is essential for defect passivation, grain recrystallization, and carrier transport optimization in CdTe thin films. In this work, MgCl 2 , TeCl 4 , and CdCl 2 treatments were implemented through two distinct thermal routes: close-spaced sublimation treatment (CSVT) and spray-assisted deposition, both followed by a controlled post-annealing step at 400 °C in a muffle furnace. The objective was to elucidate the influence of these thermal pathways on the microstructural evolution and electrical performance of CdTe absorber layers. SEM analysis revealed significant grain coalescence after chloride activation, with the average grain size increasing from 2 μm to 4 μm, along with a substantial reduction in twin boundaries and intragranular defects. GIXRD measurements evidenced enhanced crystallinity and the development of a preferential (100) texture, accompanied by a reduction in lattice parameter distortion and an increase in crystallite size, particularly for films treated via spray-assisted deposition followed by annealing at 400 °C. These structural modifications are consistent with chloride-induced recrystallization and defect redistribution mechanisms. Electrical characterization using a four-point probe demonstrated a decrease in resistivity of at least one order of magnitude compared to as-grown films, indicating improved carrier transport associated with grain boundary passivation and enhanced dopant activation. Among the evaluated conditions, the integration of CSVT or spray-based chloride incorporation with post-annealing at 400 °C produced the most effective activation, simultaneously optimizing microstructural ordering and electrical conductivity. Photovoltaic devices fabricated with MgCl 2 -treated CdTe absorbers achieved efficiencies of up to 13%, mainly due to increased current density. The spray-assisted route yielded comparable device performance, demonstrating that alternative chloride delivery methods, combined with optimized thermal consolidation, can provide an effective and scalable activation strategy for CdTe solar cells.