Indoor Dye-Sensitized Solar Cells with Efficiencies Surpassing 26% Using Polymeric Counter Electrodes

The development of high-performance counter electrodes (CEs) for bifacial dye-sensitized solar cells (DSSCs) using nonplatinum (Pt) material is important to prepare low-cost and high-power conversion efficiency (PCE) DSSCs. In this work, poly(3,4-ethylenedioxythiophene) (PEDOT) CEs were prepared by the electrochemical deposition of PEDOT onto fluorine-doped tin oxide substrates for indoor light application. To obtain a high catalytic and high transparent CE, the thickness of the PEDOT film was controlled. Using Y123 dye and cobalt redox system, the cell performance under different light intensities (200-1000 lx) was studied. The results show that the optimal thickness of PEDOT was 90 nm, which can produce higher diffusivity, higher ionic conductivity, and lower charge transfer resistance at the CE/electrolyte interface. Accordingly, PCEs of 23.98% (200 lx), 25.83% (600 lx), and 26.93% (1000 lx) were achieved for a traditional DSSC photoelectrode containing main layer (ML) and scattering layer (SL). For bifacial cells using a newly developed sandwich photoelectrode with the ML/SL/ML structure, the front-side and rear-side efficiencies under 200 lx illumination were 24.16 and 22.45%, respectively, and the rear-to-front-side efficiency ratio was 93%. These efficiencies were much higher than those obtained using Pt CE.