Hot photocarrier dynamics in organic solar cells

• Published in: Nature communications 2015-07, Vol.6 (1), p.7558-7558, Article 7558
• Main Authors: Lane, P. A., Cunningham, P. D., Melinger, J. S., Esenturk, O., Heilweil, E. J.
• Format: Article
• Language: English
• Subjects: 140/125; 639/301/299/946; 639/638/440/947; 639/766/400/561; Humanities and Social Sciences; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms8558

Photocurrent in an organic solar cell is generated by a charge transfer reaction between electron donors and acceptors. Charge transfer is expected to proceed from thermalized states, but this picture has been challenged by recent studies that have investigated the role of hot excitons. Here we show a direct link between excess excitation energy and photocarrier mobility. Charge transfer from excited donor molecules generates hot photocarriers with excess energy coming from the offset between the lowest unoccupied molecular orbital of the donor and that of the acceptor. Hot photocarriers manifest themselves through a short-lived spike in terahertz photoconductivity that decays on a picosecond timescale as carriers thermalize. Different dynamics are observed when exciting the acceptor at its absorption edge to a thermalized state. Charge transfer in this case generates thermalized carriers described by terahertz photoconductivity dynamics consisting of an instrument-limited rise to a long-lived signal. An optically excited electrical current flows through an organic solar cell by charge transfer between electron donors and acceptors. Here, the authors use terahertz photoconductivity measurements to show that any energy in excess of that needed to create these carriers can influence charge mobility