Observation of Triplet Excito Formation in a Platinum-Sensitized Organic Photovoltaic Device

Organic photovoltaics (OPVs) constitute a promising new technology due to their low production costs. However, OPV efficiencies remain low because excitons typically diffuse only similar to 5-20 nm during their lifetime, limiting the effective thickness of the light-absorbing layer. One strategy to improve OPVs is to increase exciton lifetimes by converting them into triplet states, which typically persist 10(3)-10(5) times longer than singlet excitons. We present femtosecond transient absorption and steady-state photovoltaic measurements of a model OPV system consisting of diphenyltetracene (DPT) films doped with platinum tetraphenylbenzoporphyrin (Pt(TPBP). Photoexcitation of Pt(TPBP) creates a singlet excitation that rapidly intersystem crosses to a triplet state before transfering to the DPT host matrix This transfer is rapid and efficient occurring in 35 Ps with an 85% converstion ratio of porphyrin singlets to DPT triplets. These triplet excitons lead to enhanced photocurrent response that increases with device thickness.