Enhanced charge mobility in a molecular hole transporter via addition of redox inactive ionic dopant: Implication to dye-sensitized solar cells

Abstract

Upon the addition of lithium salts to the hole-transporter matrix, $2,2^{\prime },7,7^{\prime }$ -tetrakis($N,N$ -di-$p$ -methoxypheny-amine)-$9,9^{\prime }$ -spirobifluorene (spiro-MeOTAD), the authors observe a 100-fold increase in conductivity through spiro-MeOTAD within a $\mathrm{Ti}{\mathrm{O}}_2$ mesoporous network. The authors demonstrate this to be a bulk effect and not due to improved injection at the electrodes. By testing “hole-only” diodes of pure spiro-MeOTAD and those doped with lithium salts, the authors calculate that the hole mobility increases from $1.6\times {10}^{-4}\text{to}1.6\times {10}^{-3}{\mathrm{cm}}^2∕\mathrm{V}\mathrm{s}$ . The authors discuss the possible mechanisms for this significant enhancement in charge mobility and its implication to the dye-sensitized solar cell operation.