Thermal Treatment Effects on Electrodeposited Sb₂Se₃ Photovoltaic Thin Films

Abstract

Antimony selenide thin films were prepared through potentiostatic co‐electrodeposition by applying −0.6 V from a bath composed of 2.5 mM K(SbO)C4H4O6 ⋅ 0.5 H2O and 2.0 mM SeO2 in a supporting electrolyte of 0.5 M Na2SO4/H2SO4 at pH 2. The films were subjected to different thermal treatment (TT) conditions under a Se(vapor)/N2 atmosphere. Cyclic voltammetry was used to evaluate the electrochemical process of each element separately as well as the binary system on Pt and FTO working electrodes. The morphology, composition, band gap, crystallography, and photoactivity toward hydrogen gas production of the films were evaluated as a function of TT conditions, in order to obtain insight into their effects on film properties. Under all conditions, the films showed homogeneous and rough surfaces and a stoichiometric Sb2Se3 composition. The non‐thermal‐treated film was non‐crystalline, whereas after TT, all films showed a pure orthorhombic Sb2Se3 phase. It was observed that the crystallographic texturization of films in the (120) plane, caused by some TT conditions, is detrimental to the photoactivity. At the optimized TT conditions (300 °C for 3 h), the film presented good crystallographic and optoelectronic properties and photoactivity, with a photocurrent value of 168.15 μA cm−2 (at the standard hydrogen gas evolution potential) and a band gap of around 1.1 eV.

Electrodeposition Conditions Effect Sb2Se3 Thin‐Film Properties

“…Figure 1a represents the morphology of the film grown under the initial conditions (IC), which exhibits a more globularlike shaped surface. [22] In relation to films B and C, it was verified that the amount of Se incorporated in both films was greater than the stoichiometric amount. This tendency was decreased in C-film, although it is still possible to verify the presence of small clustered rods.…”

“…The deposition potential (E d ) was studied in three levels À 0.83 (I-film), À 0.60 (IC-film) and À 0.50 V (H-film), while the bath temperatures (T) studied were 25 and 70°C. It is worth mentioning that the visual roughness seems to be associated with the deposition rate, since the film deposited at À 0.50 V, potential close to the on-set potential of the deposition wave, [22] was the most compact, while the one deposited at À 0.60 V, a potential close to the half-wave potential (E 1/2 ), showed intermediate roughness when compared to the film deposited at À 0.83 V. These parameters affected not only the morphology of the films, but also their composition, crystallinity, and the presence of secondary phases. For example, the films deposited at a deposition potential of À 0.83 V or at a bath temperature of 70°C were rougher.…”

“…To avoid film sublimation and keep its composition close to stoichiometric, a Serich atmosphere was created inside this container by means of a crucible with 0.2 g of selenium powder (more details and apparatus description can be seen in our previous work [22] ). This temperature was held for 3 h before the system is freely cooled to room temperature (which takes about 8 h).…”

“…[19,20] Amongst the works that electrodeposited the Sb 2 Se 3 , in 2012, Lai et al [13] investigated the effect of the applied potential, pH, and bath temperature on films properties. In our previous works, [22] we systematically optimized the thermal treatment of films in order to find the conditions for improving their optoelectronic and structural properties as well as the photoelectroactivity toward hydrogen gas production by water splitting. They were subsequently submitted to thermal treatment at 300°C for 5 min.…”

Electrochemical Deposition of the Single Phase TlxCu3 – xSe2 Thin Films

“…It is worth mentioning that the decrease of film crystallinity after annealing in Se atmosphere was not expected, since the crystallinity of a great variety of selenide semiconductors has been improved after such treatment. 22,25 On other hand, from 150 to 250 o C, the clusters melt and Tl begins to sublime, while the films treated at 250 and 350 o C (Figures 7c and 7d) do not have clusters and the Se content increases. To observe any phase transition during these thermal treatments, the films were characterized by XRD.…”