Novel and Stable D-A-π-A Dyes for Efficient Solid-State Dye-Sensitized Solar Cells.

Two novel organic donor-acceptor-π-acceptor sensitizers, W7 and W8, have been applied in efficient solid-state dye-sensitized solar cells (ssDSSCs). Using 2,2',7,7'-tetrakis(,-di--methoxyphenyl-amine) 9,9'-spirobifluorene (Spiro-OMeTAD) as hole-transport material (HTM), an excellent power conversion efficiency of 6.9% was recorded for W7, together with an excellent photocurrent of 10.51 mA cm and a high open-circuit voltage of 880 mV under standard AM 1.5 G illumination (100 mW cm). The solid-state solar cells based on W8 showed an efficiency of 5.2%, with a good photocurrent of 9.55 mA cm and an open-circuit voltage of 870 mV. Compared to that of the well-known WS2 sensitizer, the results show that the performance of the ssDSSC devices can be significantly improved by introducing triphenylamine moiety into their structure. In addition, results of photoinduced absorption spectroscopy show efficient dye regeneration for W7- and W8-based devices. A higher hole conductivity of the W7/HTM and W8/HTM layers compared to that of the WS2/HTM layer was observed, indicating an efficient charge transfer at the interfaces. The results obtained offer insights into the design of reliable and highly efficient ssDSSCs for large-scale applications.