Self-controlled photo-degradation in coupled chalcogenide Bi–S–Se film for solar cell applications

The present investigation involves synthesis and photo-electrochemical characterizations of the multi-chalcogenide Bi–S–Se matrices along with their binary counterparts, low energy Bi2Se3 and relatively high energy Bi2S3 semiconductors. These films were developed on FTO glass substrates through simple and cost effective galvanostatic co-deposition technique. Bi2Se3 films by virtue of its considerably high absorption coefficient and carrier density, exhibit superior photo-conversion efficiency, however, suffers from inferior stability compared to Bi2S3. In order to achieve desired photo-electrochemical properties including a reasonable compromise between PCE and stability of the materials, different compositions of nanocrystalline Bi–S–Se film matrices were subjected to various physicochemical and electrochemical characterization techniques. The self-controlled particle size/growth during the composite formulation has been reflected in FE-SEM and XRD analysis of the set of films and a modulated band gap ranging between 1.13 and 1.34 eV was obtained depending on the S loading in the matrices. Electrochemical impedance spectroscopic measurements elucidate on the charge transfer resistance at the electrode-electrolyte interface and the Mott-Schottky plots reveal the n-type nature of the synthesized films validating their suitability as photo-anode. Although the bare Bi2Se3 films display better performance in terms of photo-current output, the Bi–S–Se composite matrices prove their candidature as potentially durable anode material in solar cells, as justified by successive Tafel and chronoamperometric analysis. The performance output of the photo-anodes demonstrate that at low-level of sulfur in the sulfoselenide matrices, the conversion efficiency was reduced to 2.53% from that of Bi2Se3 (3.65%); however, the fill factor was raised to 26.32% showing better photo-response with improved photo absorption capability, and most strikingly, the photo degradation was substantially arrested by almost 10-folds in the composite matrices.