Organic Solar Cell

Wei-Fang Su (林唯芳)

Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan

Considering the growing concern about energy prices and supply in the world, in addition to concerns about global warming, it is no surprise that there has been an increasing interest in renewable energies. Worldwide solar cell production grew by 33% in 2005, from 1200 to >1600 MW. Bank Sarasin is predicting 3330 MWp cell production by 2010. Organic solar cell has many advantages over the conventional semiconductor solar cell such as the prospect of high throughput, non-vacuum processes using reel-to-reel or spray deposition, very thin and flexible cell with high energy densities. We are developing aromatic based conducting polymer incorporation with nanoparticle to have high efficiency and long term stability solar cells. The MEHPPV-CdSe hybrid was used as our control system. Temperature dependent steady-state and time resolved photoluminescence (PL) experimental studies of MEHPPV-CdSe reveals that the role of nanoparticles not only provides medium for efficient charge separation at the interface but also leads to the increase the effective conjugation length in the polymer. The strategies of enhancing interfacial interactions between polymers and nanoparticles are explored to achieve high efficiency solar cells. We have synthesized a novel hybrid materials of poly(3-hexylthiophene)/D-A linker/TiO2. Compared with neat P3HT films on TiO2, the presence of the D-A linker between P3HT and TiO2 effectively increases the quenching of photoluminescence. The TiO2 nanorods/MEH-PPV hybrid material is fabricated for solar cell applications via spin coating process. The large interfacial area between the two materials due to high surface to volume ratio of rod shape (1-D) nanocrystals ensures a more efficient charge separation that could potentially improve charge transport in photoactive materials. Power conversion efficiency (η) of 2.2 % under illumination at 565 nm and maximum external quantum efficiency of 24 % is achieved. Patterning nanoparticles in self-assembled block copolymers are under development to increase effective interfacial interactions and reduced transport path between electrodes. Poly (para-phenylene)-b- Poly (2-vinyl pyridine) (PPP-PVP) were synthesized by using sequential anionic polymerization. Semiconducting nanoparticles of cadmium sulfide (CdS) was incorporated into PPP-PVP nanostructure using in-situ synthesis of CdS in the PVP domain. Optoelectronic property of the CdS-PPP-PVP showed decreasing in bandgap and quenching in PL as compared with PPP-PVP. The results indicate the material can absorb solar energy more efficiently and increase the charge transport in the solar cell. The project is funded by National Science Council and US Airforce.