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. (C) 2019 Elsevier Ltd. All rights reserved.