Post-Assembly Atomic Layer Deposition of Ultrathin Metal-Oxide Coatings Enhances the Performance of an Organic Dye-Sensitized Solar Cell by Suppressing Dye Aggregation

• Published in: ACS applied materials & interfaces 2015-03, Vol.7 (9), p.5150-5159
• Main Authors: Son, Ho-Jin, Kim, Chul Hoon, Kim, Dong Wook, Jeong, Nak Cheon, Prasittichai, Chaiya, Luo, Langli, Wu, Jinsong, Farha, Omar K, Wasielewski, Michael R, Hupp, Joseph T
• Format: Article
• Language: English
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/am507405b

Dye aggregation and concomitant reduction of dye excited-state lifetimes and electron-injection yields constitute a significant mechanism for diminution of light-to-electrical energy conversion efficiencies in many dye-sensitized solar cells (DSCs). For TiO2-based DSCs prepared with an archetypal donor–acceptor organic dye, (E)-2-cyano-3-(5′-(5′′-(p-(diphenylamino)­phenyl)-thiophen-2′′-yl)­thiophen-2′-yl)­acrylic acid (OrgD), we find, in part via ultrafast spectroscopy measurements, that postdye-adsorption atomic layer deposition (ALD) of ultrathin layers of either TiO2 or Al2O3 effectively reverses residual aggregation. Notably, the ALD treatment is significantly more effective than the widely used aggregation-inhibiting coadsorbent, chenodeoxycholic acid. Primarily because of reversal of OrgD aggregation, and resulting improved injection yields, ALD post-treatment engenders a 30+% increase in overall energy conversion efficiency. A secondary contributor to increased currents and efficiencies is an ALD-induced attenuation of the rate of interception of injected electrons, resulting in slightly more efficient charge collection.