Polyoxometalate modified transparent metal selenide counter electrodes for high-efficiency bifacial dye-sensitized solar cells

In the development of bifacial dye-sensitized solar cells (DSSCs), the exploration of cost-beneficial transparent counter electrodes is a permanent target. Herein, we put forward a simple one-step strategy to load PW11Co polyoxometalates on graphene-like Co0.85Se (abbreviated as PW11Co-n/Co0.85Se, where n represents the concentration of PW11Co) by in situ synthesis on conductive glass substrates. Powder X-ray diffraction, IR spectroscopy, X-ray photoelectron spectroscopy, and electron microscopy techniques prove that PW11Co nanoparticles have been dispersedly deposited on Co0.85Se. The obtained PW11Co/Co0.85Se composite counter electrode (CE) material maintains excellent transparency and efficient electrocatalytic triiodide reduction performance. As a consequence, the optimized front and back efficiencies of DSSCs based on the transparent PW11Co-0.5/Co0.85Se CE could reach 7.56% and 5.82%, respectively, which are higher than those of the Pt CE (5.89% and 4.47%) and pure Co0.85Se CE (6.45% and 5.33%). To the best of our knowledge, this is the first time that polyoxometalates have been used in bifacial DSSCs. Mechanism research shows that polyoxometalates as electron aggregates can improve the charge transfer ability of selenide to the I−/I3− redox pair as well as accelerate the reduction of I3−. The present work not only offers a valuable way to design composites for electrocatalytic triiodide reduction, but also expands the application fields of polyoxometalates toward bifacial photoelectronic devices.