Solar cells sensitized by donor-linked concerted companion dyes

Abstract

Recently, concerted companion (CC) dyes have been developed by covalently linking the acceptors of organic and porphyrin dye units. Herein, a new class of CC dyes XW85 and XW86 have been designed by linking the donors of porphyrin and organic dye units with C₆H₁₂ and C₁₂H₂₄ chains, respectively. The DSSCs of XW85 based on the I₃⁻/I⁻ electrolyte show significant J_SC (17.20 mA cm⁻²) and PCE (8.96%), and XW86 exhibits higher J_SC (18.55 mA cm⁻²) and PCE (9.76%), which are also higher than those of the corresponding cosensitization systems. However, the PCEs for XW85 and XW86 are lower than that of the acceptor-linked reference dye XW76 despite the obviously larger dye adsorption amounts. Desorption studies reveal that the CC dyes may be either double-anchored or single-anchored, with the double/single anchoring ratios lying in a sequence of XW85 (1.31) < XW86 (1.88) < XW76 (6.34), consistent with that of increasing PCE. These observations indicate that the non-adsorbed sub-dye unit cannot effectively contribute to electron injection, and thus relatively large mono-anchoring proportions for XW85 and XW86 result in their relatively low J_SC, and the difference between XW85 and XW86 indicates that a longer linking chain is beneficial for partially alleviating the unfavorable single anchoring, resulting in superior performance. The results indicate that the photovoltaic behavior for the CC dyes may be further enhanced by avoiding the unfavorable alignment of the two carboxyl groups in opposite directions and thus simultaneously anchoring the two carboxyl groups, which may be realized through more rational molecular design.