## 1 Introduction  
Antimony chalcogenides, such as Sb\({}_{2}\)S\({}_{3}\), Sb\({}_{2}\)Se\({}_{3}\), Sb\({}_{2}\)(S,Se)\({}_{3}\)[1], and CuSb\({}_{2}\)Se\({}_{3}\)[2], are gaining attention within the research community as potential and promising absorber materials for thin film solar cells. In particular, antimony selenide (Sb\({}_{2}\)Se\({}_{3}\)) exhibits several advantageous characteristics that make it suitable for this role. Sb\({}_{2}\)Se\({}_{3}\) is generally considered to be an indirect bandgap semiconductor. Previous studies have reported an indirect bandgap of approximately 1.04 eV and a direct bandgap of about 1.17 eV at room temperature. Nevertheless, Sb\({}_{2}\)Se\({}_{3}\) exhibits a strong absorption coefficient, which is advantageous for photovoltaic applications. The high absorption coefficient of Sb\({}_{2}\)Se\({}_{3}\), despite its indirect bandgap, can be justified by the following considerations:  
1. Quasi-1D Crystal Structure: strong orbital interactions inside the ribbon enhance light absorption. 2. Near-Direct Optical Transitions: a close-to-direct bandgap (\(\sim\)1.1-1.2 eV) boosts absorption. 3. p-d Orbital Hybridization: strong Se 4p-Sb 5s interactions improve optical transitions. Short Exciton Diffusion Length: charges are generated close to where light is absorbed. 5. High Optical Density of States: enhancement of photon absorption [1]. These factors make Sb\({}_{2}\)Se\({}_{3}\) behave more like a quasi-direct bandgap material with an E\({}_{\text{g}}\) of 1.17 eV [3] that lies within the range for maximum efficiencies in the Shockley-Queisser (SQ) model [4]. Additionally, the innocuous nature and abundance of antimony selenide on the Earth's crust suggest great potential for commercialization [5; 6]. Sb\({}_{2}\)Se\({}_{3}\) has a high absorption coefficient (\(\alpha\) > 10\({}^{5}\) cm\({}^{-1}\)), which allows for thinner absorber layers; furthermore, the absence of polymorphism and a low melting point (885 K) facilitate efficient synthesis by different deposition techniques, such as Chemical Bath Deposition (CBD), Close-Spaced Sublimation (CSS), Vapor Transport Deposition (VTD), Rapid Thermal Evaporation (RTE), Ion Vapor Deposition (IVD), and Radio-Frequency Magnetron Sputtering (RFMS) [1; 7; 8]. On the other hand, the deposition of antimony selenide presents challenges, particularly regarding its sensitivity to the substrate [9], its tendency to form defects [10; 11], and the occurrence of stoichiometric deviations [12]. These negative issues are reflected in low and highly anisotropic mobility, as well as self-compensation, which constitutes an impediment to extrinsic doping. State-of-the-art devices have partially addressed these challenges by careful control of the preferential orientation [13], band offset tuning [14], passivation of interface defects [15], and reduction of contact barriers [16]. These efforts led to the current record efficiency of 10.57% [17]. Research efforts were especially focused on enhancing Fill Factor (FF) and short-circuit current density (J\({}_{\text{sc}}\)), which are both now over 70% of their SQ limits. However, no similar progress was achieved in increasing the V\({}_{\text{oc}}\), which represents a notable problem for further efficiency improvements. Indeed, many reported devices in the literature exhibit a V\({}_{\text{oc}}\) close to 50% of the SQ limit [18]. Understanding the causes behind this V\({}_{\text{oc}}\) deficit is imperative for increasing the efficiency of Sb\({}_{2}\)Se\({}_{3}\) solar cells. This study employs sputtering and closed-space sublimation (CSS) for thin-film deposition, which offers key advantages over conventional methods. Sputtering, a PVD technique, ensures high film uniformity, precise thickness control, and strong adhesion, making it ideal for depositing high-purity layers. Compared to solution growth methods, it provides superior structural integrity.