Cosensitization process effect of D-A-π-A featured dyes on photovoltaic performances

Cosensitization based on two or multiple dyes as “dye cocktails” can hit the target on compensating and broadening light-harvesting region. Two indoline D-A-π-A motif sensitizers ( WS-2 and WS-39 ) that possess similar light response area but distinctly reversed feature in photovoltaic performance are selected as the specific cosensitization couple. That is, WS-2 shows quite high photocurrent but low photovoltage, and WS-39 gives relatively low photocurrent but quite high photovoltage. Due to the obvious “barrel effect”, both dyes show medium PCE around 8.50%. In contrast with the previous cosensitization strategy mostly focused on the compensation of light response region, herein we perform different cosensitization sequence, for taking insight into the balance of photocurrent and photovoltage, and achieving the synergistic improvement in power conversion efficiency (PCE). Electronic impedance spectra (EIS) indicate that exploiting dye WS-39 with high V_OC value as the primary sensitizer can repress the charge recombination more effectively, resulting in superior V_OC rather than using dye WS-2 with high J_SC as the primary sensitizer. As a consequence, a high PCE value of 9.48% is obtained with the delicate cosensitization using WS-39 as primary dye and WS-2 as accessory dye, which is higher than the corresponding devices sensitized by each individual dye (around 8.48–8.67%). It provides an effective optimizing strategy of cosensitization how to combine the individual dye advantages for developing highly efficient solar cells.