Fabrication of cellulose paper-based counter electrodes for flexible dye-sensitized solar cells

Here, we introduce the synthesis and deposition of organic/inorganic composite ink on cellulose paper using a rapid ultrasonic spray deposition approach that can be incorporated as a counter electrode (CE) in flexible dye-sensitized solar cells (FDSSCs). The composite ink comprised a copper indium sulfide (CuInS₂) nanostructure ink and dispersion of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) in water. Fabricated counter electrodes are biodegradable, environment-friendly, flexible, and economical and meet the requirements for sustainable green energy. To evaluate the catalytic activities and power conversion efficiencies of DSSCs, the produced CuInS₂/PEDOT:PSS composite ink-based CEs were compared with PEDOT:PSS counter electrodes. Cyclic voltammetry studies found that CuInS₂/PEDOT:PSS had a greater cathodic charge transfer current density (J_c) (-1.23 mA cm^-2). Moreover, it was found that the potential separation values are small, which indicate a stronger catalytic activity than PEDOT:PSS counter electrodes. The observed exchange current density (J₀) was 3.98 mA cm^-2, while the limiting current density (J_lim) increased to 45.7 mA cm^-2, indicating a fast redox diffusion rate of the CuInS₂/PEDOT:PSS CE. The photovoltaic performances of CuInS₂/PEDOT:PSS and PEDOT: PSS-based DSSC's were measured and determined to be 5.66% and 4.41%, respectively, while the performance of CuInS₂/PEDOT:PSS FDSSC composed of cellulose paper was 1.06%.