Effect of chenodeoxycholic acid as dye co-adsorbent and ZnO blocking layer in improving the performance of Rose Bengal dye based dye sensitized solar cells

Abstract

Effective suppression of dye aggregation on the photoanode surface of dye sensitized solar cells plays a key role in improving solar cell efficiency. Chenodeoxycholic acid (CDCA) is a very popular anti dye aggregation material used in dye sensitized solar cells (DSSC). However, the selection of an improper concentration of CDCA may lead to decreased solar cell efficiency by lowering the open circuit voltage and short circuit current as a consequence of reduced dye loading. The influence of CDCA as a dye co-adsorbent on the performance of DSSCs fabricated using Rose Bengal dye was studied in this paper. The concentration of the CDCA solution was varied to identify the optimum value for the best device performance. Aside from this, the effect of a very thin and compact ZnO blocking layer was also investigated to reduce the charge recombination. With photovoltaic parameters such as short circuit current density (Jsc) = 1.98 mA/cm2, open circuit voltage (Voc) = 0.58 V, and fill factor (FF) = 0.43, the traditional cell displayed an overall conversion efficiency of 0.49%, while the power conversion efficiency was found to be increased to 1.00% (Jsc = 2.80 mA/cm2, Voc = 0.64, FF = 0.58) when CDCA was added at optimised concentration of 8 mM. Reduced dye aggregation and increased electron injection in the presence of CDCA may be accounted for the DSSC's remarkable improvement in the efficiency. Moreover, the combined effect of 8 mM CDCA and the compact ZnO blocking layer dramatically enhanced the efficiency further to 1.22% (Jsc = 3.09 mA/cm2, Voc = 0.66, FF = 60). Electrochemical impedance spectroscopic (EIS) analysis revealed that the addition of CDCA as a co-adsorbent in the dye solution and addition of ZnO blocking layer resulted in significantly improved electron lifetime and reduced electron recombination yielding improved Jsc, Voc and η.