Donor Engineering of D–π–A Organic Sensitizers for Enhanced Indoor Dye‐Sensitized Solar Cells Using Copper‐Based Electrolytes

ABSTRACT Herein, we have designed and synthesized two novel metal‐free organic D‐π‐A dyes with 6‐methoxy‐N‐(4‐(methylthio)phenyl)‐N‐phenylnaphthalen‐2‐amine (SP‐3) and N‐(4‐(methylthio)phenyl)‐N‐phenylpyren‐2‐amine (SP‐4) as the donor moiety, cyanoacrylic acid as the anchoring unit and thiophene as the π‐spacer. Both SP‐3 and SP‐4 based DSCs reproduced efficiencies of 4.06% and 3.58% under standard 1 sun illumination, and an in‐depth interfacial charge transfer study revealed the influence of oxygen‐linked naphthalene donor unit on the electron diffusion within the TiO 2 scaffold, pushing charge collection efficiency (ηcc) above 50% for SP‐3 based DSC. Further, co‐sensitization with XY1b dye enhances the device performance with a PCE of 6.02% under 1 sun illumination. Improved lifetime and faster electron transport/diffusion helped SP‐3:XY1b to achieve an efficiency at par with SP‐4:XY1b even with a lower fill factor (FF) below 50. However, lower FF, which is an indication of severe recombination within the system, becomes prominent under lower illumination intensities, where SP‐4:XY1b superseded SP‐3:XY1b with a PCE of 31.37% under standard 1000 lux WW CFL illumination. A complete indoor performance analysis was carried out for the co‐sensitized devices, and SP‐4:XY1b gives a PCE above 27% under various illumination intensities (1000, 700, 500, 200 lux) and sources (WW CFL, WW LED, DL LED).