MATERIAL REQUIREMENTS FOR ORGANIC SOLAR CELLS. THE STRUCTURE - PROPERTY CORRELATION OF LOW-BANDGAP TRANSPORTERS
M. Morana, M. Koppe, M.C. Scharber, Z. Zhu, R. Gaudiana, D. Waller, C.J. Brabec
Affiliation: Konarka Technologies
For bulk heterojunction photovoltaic cells fabricated from conjugated polymers and a fullerene derivative, the relation between the open circuit voltage (Voc) and the oxidation potential of different conjugated polymers is linear. Based on this finding the optimized energy conversion efficiency of a bulk-heterojunction solar cell is derived as a function of the band-gap and the energetic levels of the conjugated polymer, allowing to discuss and define the material parameters for a 10 % material. As one promising candidate for a high efficiency polymer a novel low-bandgap conjugated polymer, a bridged poly bithiophene derivative (PCPDTBT), is introduced. PCPDTBT shows high photovoltaic quantum efficiencies in the near infrared spectral region. The optical bandgap of 1.4 eV combined with excellent mobility up to 1.5 x 10-2 cm2 /Vs and good processability makes this material ideal for organic single junction solar cells. The correlation between the transport properties and the device performance will be discussed in this presentation.