title: Observation of Triplet Exciton Formation in a Platinum-Sensitized Organic Photovoltaic Device.
abstract: Organic photovoltaics (OPVs) constitute a promising new technology due to their low production costs. However, OPV efficiencies remain low because excitons typically diffuse only ∼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 transferring to the DPT host matrix. This transfer is rapid and efficient, occurring in 35 ps with an 85% conversion ratio of porphyrin singlets to DPT triplets. These triplet excitons lead to enhanced photocurrent response that increases with device thickness.
authors: Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States.
authors: Sean T
authors: ST
authors: Roberts
authors: Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States.
authors: Cody W
authors: CW
authors: Schlenker
authors: Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States.
authors: Vincent
authors: V
authors: Barlier
authors: Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States.
authors: R Eric
authors: RE
authors: McAnally
authors: Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States.
authors: Yuyuan
authors: Y
authors: Zhang
authors: Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States.
authors: Joseph N
authors: JN
authors: Mastron
authors: Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States.
authors: Mark E
authors: ME
authors: Thompson
authors: Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States.
authors: Stephen E
authors: SE
authors: Bradforth
keywords: intersystem crossing; photovoltaic; platinum porphyrin; thin-film device; transient absorption; triplet energy transfer; triplet sensitization