Abstract: Polycrystalline metal chalcogenide (CdS, CdSe, CdTe, CuS, CuSe and others) thin-film electrodes are being considered as alternative for the more costly and advanced-tech demanding photovoltaic (PV) systems. Despite their ease of preparation and economy in starting materials, the thin film electrodes have major drawbacks. Due to lack of surface uniformity, low carrier mobility and high resistance at the solid/liquid interface, such electrodes exhibit low conversion efficiency in PEC processes. Moreover, the electrode surfaces are unstable and tend to undergo photo-corrosion. These shortcomings are a real challenge for using thin film electrodes in PEC technology, and should be overcome. Porphyirinato manganese (MnTPyP) complexes embodied inside different polymeric materials have been used as charge transfer mediators across solid/liquid junctions in PEC processes. The MnTPyP/Polymer coating (~80 nm thick) can be cast onto surfaces of the polycrystalline metal chalcogenide thin film electrodes in simple methods. The coating showed remarkable enhancement in the PEC conversion efficiency of different electrodes. Both shot-circuit current and fill factor values have been remarkably enhanced. Conversion efficiency values of as high as 19% have been observed here. Such results have not been preceded before in metal chalchogenide thin-film electrode processes. Moreover, the coating enhanced the semiconductor electrode stability to photo-corrosion under PEC conditions. The MnTPyP/Polymer matrix behaved as charge transfer mediator across the solid/liquid interface. Upon exciting an n-type semiconductor electrode, electrons are excited from the valence band to the conduction band and move to the back contact wiring. The remaining holes must move to the redox couple to make photo-current. In polycrystalline semiconductor electrodes, such a transfer is not fast enough, which lowers the value of the short circuit current, and consequently the conversion efficiency. Therefore, holes accumulate in the space charge layer and cause electrode corrosion. The MnTPyP/Polymer matrix enhances both efficiency and stability of the electrode by behaving as a charge transfer mediator. The MnTPyP complex involves both MnIII and MnII ions together. The holes in the valence band oxidize the MnII ions into MnIII ions. The MnIII ions in turn oxidize the reduced phase of the redox couple. By this way, the MnTPyP complex catalyzes the hole-transfer and enhances both efficiency and stability of the electrode. The charge transfer mediation formalism is summarized in the attached Scheme. Results and discussions will be presented in detail together with effect of the coating on the electrode band edge positions.

Conference Title

18th International Meeting on Lithium Batteries, June 19-24, 2016, in Chicago, Illinois, USA

Conference Country

Palestine

Conference Date

June 19, 2016 - June 24, 2016

Conference Sponsor

Electrochemical Society

Additional Info

Conference Website