Unravelling the bottleneck of phosphonic acid anchoring groups aiming toward enhancing the stability and efficiency of mesoscopic solar cells

Abstract

Novel near-infrared sensitizers with different anchoring groups aiming toward improved stability and efficiency of dye-sensitized solar cells were synthesized. Adsorption of these dyes on the mesoporous TiO₂ surface revealed the dye adsorption rate of –CH=CH–COOH (SQ-139)>–CH=C(CN)COOH (SQ-140)>–PO₃H₂ (SQ-143)>–CH=C(CN)PO₃H₂ (SQ-148)>–CH=C(CN)PO₃H–C₂H₅ (SQ-157)>–PO₃H–C₂H₅ (SQ-151)> –CH=CH–COOH(–PO₃H₂) (SQ-162). The binding strength of these dyes on mesoporous TiO₂ as investigated by dye desorption studies follows SQ-162>SQ-143>SQ-148>SQ-139≫SQ-157~SQ-151≫SQ-140 order. The acrylic acid anchoring group was demonstrated to be an optimum functional group owing to its fast dye adsorption rate and better binding strength on TiO₂ along with good photoconversion efficiency. Results of dye binding on TiO₂ surface demonstrated that SQ-162 bearing double anchoring groups of phosphonic and acrylic acid exhibited>550 times stronger binding as compared to dye SQ-140 having cyanoacrylic acid anchoring group. SQ-140 exhibited the best photovoltaic performance with photon harvesting mainly in the far-red to near-infrared wavelength region having short circuit current density, open-circuit voltage and fill factor of 14.28 mA·cm^–2, 0.64 V and 0.65, respectively, giving the power conversion efficiency of 5.95%. Thus, dye SQ-162 not only solved the problem of very poor efficiency of dye bearing only phosphonic acid while maintaining the extremely high binding strength opening the path for the design and development of novel near-infrared dyes with improved efficiency and stability by further increasing the π-conjugation.

Graphical abstract

Keywords

anchoring groups / adsorption behaviour / dye-binding strength / squaraine dyes / dye-sensitized solar cells

RIGHTS & PERMISSIONS

Higher Education Press