Letter abstract
Nature Materials 4, 37 - 41 (2004)
Published online: 12 December 2004 | doi:10.1038/nmat1285
Subject Categories: Polymers | Semiconductors | Optical, photonic and optoelectronic materials | Materials for energy
Controlled growth of a molecular bulk heterojunction photovoltaic cell
Fan Yang1, Max Shtein2 & Stephen R. Forrest1
The power conversion efficiency of organic photovoltaic cells has increased with the introduction of the donor–acceptor heterojunction that serves to dissociate strongly bound photogenerated excitons1. Further efficiency increases have been achieved in both polymer2, 3 and small-molecular-mass4 organic photovoltaic cells through the use of the bulk heterojunction (BHJ), where the distance an exciton must diffuse from its generation to its dissociation site is reduced in an interpenetrating network of the donor and acceptor materials. However, the random distribution of donor and acceptor materials in such structures can lead to charge trapping at bottlenecks and cul-de-sacs in the conducting pathways to the electrodes. Here, we present a method for growing crystalline organic films into a controlled bulk heterojunction; that is, the positions and orientations of donor and acceptor materials are determined during growth by organic vapour-phase deposition (OVPD5), eliminating contorted and resistive conducting pathways while maximizing the interface area. This results in a substantial increase in power conversion efficiency compared with the best values obtained by 'random' small-molecular-weight BHJ solar cells formed by high-temperature annealing, or planar double heterojunction photovoltaic cells using the same archetypal materials systems.
- Department of Electrical Engineering, Princeton Institute for the Science and Technology of Materials (PRISM), Princeton University, Princeton, New Jersey 08544, USA
- Department of Chemical Engineering, Princeton Institute for the Science and Technology of Materials (PRISM), Princeton University, Princeton, New Jersey 08544, USA
Correspondence to: Stephen R. Forrest1 e-mail: forrest@princeton.edu
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