1. Title : Polymer Solar Cells with Efficient Active Layer via Concentration graded Solution Process, Stamping Transfer Technique and Controlled Nano-Structure<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

2. Speaker : Prof. O Ok Park (Dept. of Chemical & Biomolecular Engineering, Korea Advanced Institute of Science and Technology)

3. Date : March 29 (Mon), <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />5:00~6:15 P.M.

4. Venue : Building 302, Room 720

5. Educational Background :

1982–1985  Ph.D. Stanford University

1976–1978  M.S. Korea Advanced Institute of Science and Technology

1972–1976  B.S. Seoul National University

6. Contact : Prof. Jyongsik Jang (☏880-8927)

7. Abstract :

It is well known that energy consumption is increasing rapidly but the fossil energy sources are very much limited. Therefore, new approaches for development of the sustainable energy sources are definitely urgent and one of them could be the solar energy system for its unlimited and complete source of energy which can be used as a source for light, heat and electricity. Several different solar cells are under consideration by a lot of researchers all over the world such as silicon semiconductor, compound semiconductor, organic solar cells, and dye sensitized solar cells. Among them, polymer based solar cells with donor-acceptor active layer is a quite attractive and prospective device for its flexibility, semi-transparency and low-cost possibility.

Here, we have focused on how to improve not only the efficiency and low vacuum processability (1) but also to enhance high-temperature long term stability and durability in photovoltaic devices with thermally stable titanium oxide interlayer. It can be demonstrated by introducing a protective layer of linear polymeric TiOx which is attributed to an improved interfacial stability owing to relatively reduced morphology change even at high temperature operation (2). Also the bilayer active film with a concentration gradient has been successfully fabricated via solution process for the first time. The concentration variation has been confirmed by the Auger spectroscopy. The novel device showed an enhanced photocurrent density and power conversion efficiency compared to those of the BHJ PV prepared under the same fabrication condition (3). Additionally, we devised novel process of stamping transfer technique of a bulk-hetero-junction (BHJ) active layer with help of UV-curable resin-coated polycarbonate (UV-PC) film (4). The ratio controlled double printed BHJ active layer was also studied to find out optimum bilayer device conditions with efficient charge generation and collection property (5). From the device with controlled nano-structure point of view, a patterned conducting IZO film with well-ordered periodic dot-structures with 50 nm or 200 nm deep features has been constructed by nano-imprinting technique as the anode of an photovoltaic device. The highly ordered 2D-dot nano-patterned anode can enhance the device performance due to the large interfacial area between both of the electrodes and the active layer. Furthermore, nano-patterned structures can efficiently harvest electrons and holes from the active layer to each electrode in the IZO anode and Al cathode (6). Finally, We have demonstrated a simple and non lithographic method that enlarges the active layer / metal electrode contact area in polymer solar cells by adding the thermal initiator 2,2’'-azobisisobutyronitrile (AIBN) as a nano-hole generating agent. The device performance enhancement comes not from a change in the charge carrier generation or transportation characteristics but from increased charge carrier collection due to the reduced contact resistance and shortened pathway to the electrode caused by enlarged interfacial area. (7)

1. S. J. Yoon, J. H. Park, H. K. Lee and O O. Park, APL, 92, (2008) 143504

2. D. H. Wang, S. H. Im, H. K. Lee, J. H. Park and O O. Park, J. Phy. Chem. C, 113, (2009) 17268

3. D. H. Wang, D. G. Choi, H. K. Lee, J. H. Park, and O O. Park, Appl. Phys. Lett. 95 (2009) 043505

4. D. H. Wang, D. G. Choi, K. J. Lee, J. H. Park and O O. Park, Langmuir In Revision (2010)

5. D. H. Wang, D. G. Choi, K. J. Lee, J. H. Park and O O. Park, Org. Electron. In Press (2010)

6. D. H. Wang, D. G. Choi, K. J. Lee, J. H. Park and O O. Park, Org. Electron. 11 (2010) 285

7. H. K. Lee, J. H. Jeon, D. H. Wang, J. K. Kim, S. H. Im, J. H. Park and O O. Park, APL, In Press (2010).