Two-step Deposition Strategy Research Articles

Regulating Deposition Pressures During Rapid Thermal Evaporation Processes to Enable Efficient Sb2 Se3 Solar Cells.

Sb2 Se3 solar cells deposited by rapid thermal evaporation (RTE) have drawn extensive attention owing to their compatibility with the commercial production line of CdTe solar cells and can be used to fabricate high-quality Sb2 Se3 films with high reproducibility. However, the deposition pressure during the RTE process has not been clearly explored, although it has a significant effect on the Sb2 Se3 film quality. A novel two-step deposition strategy is proposed that finely regulates the deposition pressure to improve the quality of Sb2 Se3 absorber layers, thereby improving the device performance of Sb2 Se3 solar cells. This novel method includes a rapid deposition process under a low pressure (5 mTorr) and an in situ annealing process under a relatively high pressure (200Torr). The maximum power conversion efficiency (PCE) of Sb2 Se3 solar cells fabricated by two-step deposited approach is up to 8.12%. The PCE enhancement is attributed to the increased grain size, reduced grain boundaries, modified surface Fermi level gradient of the absorber layer, and improved defect performance. This innovative deposition technique is expected to benefit other low-melting-point metal sulfoselenides for solar cell applications.

Atomic-level understanding layer-by-layer formation process of TiCx on carbon film

TiCx coating film was fabricated by a novel two-step deposition strategy in molten salts media, namely carbon film was prepared firstly on the substrate and then following transformation of C to TiCx by deposition of Ti on the C film. The latter step was achieved by electrochemical deposition of Ti in FLiNaK-K2TiF6-Ti, in which the Ti2+ ion was the dominant species. It was found that the transformation of C to TiCx is a diffusion control process rather than deposition control one, implying that the interdiffusion between Ti and C phase is the decision step. To reveal the formation process, calculation simulation was further conducted. The results of first-principle calculation demonstrate that the deposited Ti atom prefers to combine to the central site of the graphite surface. Then, formation of Ti layer will take place as the atom number increased by continuous deposition. Subsequently, the interdiffusion between Ti and C phase motivated by repulsion, concentration gradient and Gibbs free energy will contribute to the transformation of composite. Such initial formation process of TiCx on the C film was further confirmed by the results of charge transfer between Ti and C atoms and its electronic state. The results of deposition and diffusion of Ti and C atoms manifest that the formation of TiCx is a reconstruction rather than atom diffusion process.