Deep Energetic Trap States in Organic Photovoltaic Devices

TitleDeep Energetic Trap States in Organic Photovoltaic Devices
Publication TypeJournal Article
Year of Publication2012
AuthorsC.G. Shuttle, N.D. Treat, Jessica D. Douglas, Jean M. J. Frechet, and M.L. Chabinyc
Date PublishedJAN
Keywordscharge transport, disorder, PCBM, solar cells, trapping
AbstractThe nature of energetic disorder in organic semiconductors is poorly understood. In photovoltaics, energetic disorder leads to reductions in the open circuit voltage and contributes to other loss processes. In this work, three independent optoelectronic methods were used to determine the long-lived carrier populations in a high efficiency N-alkylthieno[3,4-c]pyrrole-4,6-dione (TPD) based polymer: fullerene solar cell. In the TPD co-polymer, all methods indicate the presence of a long-lived carrier population of similar to 10(15) cm-3 on timescales = 100 mu s. Additionally, the behavior of these photovoltaic devices under optical bias is consistent with deep energetic lying trap states. Comparative measurements were also performed on high efficiency poly-3-hexylthiophene (P3HT): fullerene solar cells; however a similar long-lived carrier population was not observed. This observation is consistent with a higher acceptor concentration (doping) in P3HT than in the TPD-based copolymer.