Engineering of organic dyes for highly efficient p-type dye-sensitized solar cells

Four organic dyes, namely T3, T3H, T4 and T4H, are designed and synthesized for p-type photocathodes. Different from the widely explored method of extending conjugation between donor and acceptor, in these dyes, the distance between donor and the semiconductor surface is elongated by three or four alkylated thiophene units. Dicyanovinyl and 1,3-diethyl-2-thiobarbituric acid are introduced as the acceptor units, respectively. It turns out that the increased oligothiophene units between triphenylamine and carboxylate enhances the light harvesting efficiency. Moreover, the thiobarbituric acid offers much broader and stronger absorption reaching the NIR region, thus leading to higher photocurrents in T4H. As a result, dye T4H shows the highest power conversion efficiency of 0.317%, with photocurrent up to 6.735 mA/cm(2) using the I-/I-3(-) electrolyte. Notably, the high photocurrent obtained is close to the highest value reported to date for p-type dye-sensitized solar cells (7.57 mA/cm(2)). (C) 2015 Elsevier Ltd. All rights reserved.