Efficacy of TiOx optical spacer in bulk-heterojunction solar cells processed with 1,8-octanedithiol

The efficacy of $\mathrm{Ti}{\mathrm{O}}_x$ as an optical spacer in bulk-heterojunction (BHJ) solar cells made from regioregular poly(3-hexylthiophene) and [6,6]-phenyl ${\mathrm{C}}_{61}$ -butyric acid methyl ester films processed with 1,8-octanedithiol is investigated. The results indicate that the enhanced efficiency resulting from the $\mathrm{Ti}{\mathrm{O}}_x$ optical spacer is anticorrelated to the concentration of the processing additive. The use of the processing additive induces surface roughness on the BHJ film and thereby diminishes the efficacy of the optical spacer. Solar cells fabricated with both the optical spacer and 1,8-octanedithiol yield efficiencies that are superior to those with either process alone.