Perylenes are well‐known pigments with excellent chemical, thermal, and photochemical stabilities and have been used in various optical and electronic fields. Although for sensitized mesoscopic solar cells there is rapid progress of metal‐free thiophene dyes, which now reach over 11.5% power conversion efficiency (PCE) at air mass 1.5 global (AM1.5G) conditions, the so far reported highest PCE of a perylene dye is only 6.8%. Here, a new metal‐free organic donor‐acceptor (D‐A) dye (C261) featuring a bisarylamino functionalized N‐annulated perylene electron‐releasing segment and a cyanoacrylic acid electron‐withdrawing unit is synthesized. Combining a mesoporous titania film grafted by this structurally simple perylene dye with a non‐corrosive cobalt redox shuttle, an 8.8% PCE is achieved at an irradiance of the AM1.5G sunlight. By selecting the model dye G221 as a reference, theoretical calculations, steady‐state and time‐resolved spectroscopies, and electrical measurements are used to compare the energy‐levels, light absorptions, and mutichannel charge transfer dynamics that contribute to the photovoltaic behavior.

The usage of coplanar π-conjugated segments represents a feasible strategy on reducing the energy gap of organic push−pull dyes for mesoscopic titania solar cells. In this paper, we report two new dyes coded as C254 and C255 with the respective 1,4di(thiophen-2-yl)benzene and indacenodithiophene π-linkers, in combination with the electron-releasing triphenylamine and electron-withdrawing cyanoacrylic acid units. The energy-gap reduction stemming from the rigidity of the π-linker is accompanied by a negative shift of the ground-state redox potential, which however does not affect the yield of hole injection from the oxidized state of dye molecules to a cobalt redox electrolyte. On the other side, we have identified from femtosecond transient absorption measurements a diminished rate of electron injection from the relaxed, low-energy excited state of C255 to titania, albeit a comparable rate of electron injection from the high-energy excited states of these two dyes. The bulkier C255 dye with four hexyl side chains tethered on the two sp 3 carbons of the fused indacenodithiophene unit can form a more compact self-assembling monolayer on titania, considerably attenuating the charge recombination of photoinjected electrons in titania with the cobalt electrolyte and thus enhancing the cell photovoltage and efficiency.