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1031-H09-36

Efficient Thin Polymer Solar Cells with Post-Annealing Shun-Wei Liu1, Chih-Chien Lee2, Ping-Tsung Huang3, Chin-Ti Chen1, and Juen-Kai Wang4,5 1 Institute of Chemistry, Academia Sinica, Taipei, 11542, Taiwan 2 Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei, 106, Taiwan 3 RiTdisplay Corporation, Hsin-Chu, 303, Taiwan 4 Center for Condensed Matter Sciences, National Taiwan University, Taipei, 106, Taiwan 5 Institute of Atomic and Molecular Science, Academia Sinica, Taipei, 106, Taiwan ABSTRACT The development of high-performance organic solar cells with low-cost fabrication processes has become one of the most important tasks in the vast endeavors of releasing the world-wide energy demand from fossil fuels. Nowadays, the power-conversion efficiency of polymer solar cells in excess of 5% has been demonstrated, but they involve complicated film formation mechanisms of thick active layers or delicate design of spacer layers. These approaches, therefore, may increase the series resistance of the devices and complicate fabrication procedure. In this report, we present a highly efficient polymer solar cells with a bulk heterojunction layer of poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methylester (P3HT:PCBM) which is annealed at 130°C for 5 min. in a nitrogen environment (O2 < 0.1 ppm and H2O < 0.1 ppm) before cathode deposition. The annealing temperature is much lower and the annealing time is shorter than previous works. The device exhibits conversion efficiency of 4.9%, fill factor of 53 %, and open-circuit voltage of 0.67 V. These values are still comparable with the highest values reported previously. The annealing process is expected to modify the network morphology of the P3HT:PCBM layer. Finally, the thickness of the active layer is reduced to 50 nm which is much thinner than previously reported values, may facilitating the fabrication of tandem photovoltaic structures. INTRODUCTION To provide a truly widespread primary energy source, solar cells have been made from many inorganic materials with various device configurations, such as single-crystal, polycrystalline, and amorphous thin-film structures [1-3]. However, these solar energy devices are very expensive for electrical power generation. Organic solar cells have recently attracted much attention due to their advantages such as simple device structure, low-cost materials of tunable band gap, and compatibility with large-area flexible substrates [4-6]. In fact, the energy conversion mechanisms of organic solar cells make use of the transformation of photogenerated excitons into free charge carriers at donor-acceptor heterojunctions. An efficient organic heterojunction device was proposed in 1986 when Tang used two materials with different electron affinities and ionization potentials [4]. At the interface, the resulting potentials are strong and may favor exciton dissociation. Therefore, in this device the excitons should be formed within the diffusion length of the interface, which can co