Sb2(S,Se)3, is becoming a relevant critical-raw-materials free semiconductor with different technological applications such as: superconductivity, electronic component, electrode for sodium-ion batteries, photodetectors and as emerging thin film photovoltaic absorber. In particular, and for this last application, the material has shown remarkable improvements in the last few years, demonstrating solar cells in superstrate configuration with power conversion efficiencies reaching 7.6%1. This has open interesting perspectives for their use in solar energy conversion applications, also taking into account the 1D crystalline organization of the material, with in principle benign grain boundaries and anisotropic conduction properties2. Additionally Sb2Se3 has shown a high flexibility degree in terms of substrate type, due to the relatively low synthesis temperature (300-400 ºC), allowing deposition onto polymeric, steels, ceramics and TCO/glass substrates. This versatility makes this compound very promising for ubiquitous applications such as building integrated photovoltaics (BIPV) (flexible, bifacial, and semi-transparent), wearables, or autonomous IOT applications among others. In this work we present a systematic optimization study of the synthesis of Sb2Se3 thin films using substrate configuration solar cells, by a sequential process based on reactive annealing under Se atmosphere of thermally evaporated Sb layer precursors. The study is centered in the analysis of Sb precursor thickness and reactive thermal annealing conditions (annealing temperature, time, and pressure) on the compositional, structural and morphological properties of the layers. After a first optimization on Mo coated soda lime glass substrates, we report a promising power conversion efficiency of 5.3% in substrate configuration (Figure 1), close to the 7.6% certified world record in superstrate one. Additionally the study is complemented with a wide characterization of the fundamental properties of Sb2Se3 layers and devices using morphological and physic-chemical characterization (Photoluminescence, SEM, XRF, XRD and multi-wavelength Raman spectroscopy), as well as optoelectronic characterization (JV, IQE, CV) of the solar cells.