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Pure Appl. Chem., 2010, Vol. 82, No. 11, pp. 2121-2135

Published online 2010-08-06

Excitation energy transfer in conjugated polymer/silicon nanocrystal-based bulk heterojunctions

Vladimir Švrček

Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan

Abstract: An excitation energy transfer in a bulk heterojunction based on freestanding silicon nanocrystals (Si-NCs) and conjugated polymers {poly(3-hexylthiophene) (P3HT), poly[2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV)} is demonstrated. The electrochemical etching process is employed for fabrication of freestanding and polymer soluble Si-NCs. Formation of a bulk heterojunction is confirmed by a difference in a work function of both polymers and an ionization potential of the NCs. An annealing step significantly influences the polymer chain conformation and electronic interaction between the polymer and the NC, which improves the exciton energy migration. The presence of the Si-NCs in polymers suppresses the relative intensity of vibronic peaks, resulting in a red-shift of the blend photoluminescence (PL) spectra. This phenomenon is attributed to a temperature-dependent migration process of singlet exciton and Dexter excitation energy transfer from the polymer to the NC. Compared to MEH-PPV polymer, a lamella-type stacking structure of the P3HT and an abridged PL spectra overlap with NCs decreases an excitation energy transfer rate. At the same time, an improvement in photocurrent generation is recorded when Si-NCs are embedded in P3HT polymer. After Dexter-like excitonic energy transfer, the PL emission of both blends is controlled through a quantum confinement effect and electron-hole recombination in Si-NCs.