Role of Intrinsic Photogeneration in Single Layer and Bilayer Solar Cells with C-60 and PCBM

Hahn, Tobias and Tscheuschner, Steffen and Saller, Christina and Strohriegl, Peter and Boregowda, Puttaraju and Mukhopadhyay, Tushita and Patil, Satish and Neher, Dieter and Baessler, Heinz and Koehler, Anna (2016) Role of Intrinsic Photogeneration in Single Layer and Bilayer Solar Cells with C-60 and PCBM. In: JOURNAL OF PHYSICAL CHEMISTRY C, 120 (43). pp. 25083-25091.

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Abstract

In an endeavor to examine how optical excitation of C-60 and PCBM contribute to the photogeneration of charge carriers in organic solar cells, we investigated stationary photogeneration in single-layer C-60 and PCBM films over a broad spectrum as a function, of the electric field. We find that intrinsic photogeneration starts at a photon energy of about 2.25 eV, i.e., about 0.4 eV above the first singlet excited state. It originates from charge transfer type states that can autoionize before relaxing to the lower-energy singlet Si state, in the spirit of Onsager's 1938 theory. We analyze the internal quantum efficiency as a function of electric field and photon energy to determine (1) the Coulombic binding and separation of the electron hole pairs, (2) the value of the electrical gap, and (3) which fraction of photoexcitations can fully separate at a given photon energy. The latter depends on the coupling between the photogenerated charge transfer states and the eventual charge transporting states. It is by a factor of 3 lower in PCBM. Close to the threshold energy for intrinsic photoconduction (2.25 eV), the generating entity is a photo generated electron-hole pair with roughly 2 nm separation. At higher photon energy, more expanded pairs are produced incoherently via thermalization.

Item Type:	Journal Article
Publication:	JOURNAL OF PHYSICAL CHEMISTRY C
Additional Information:	Copy right for this article belongs to the AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited:	21 Dec 2016 07:25
Last Modified:	21 Dec 2016 07:25
URI:	http://eprints.iisc.ac.in/id/eprint/55533

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