Photovoltaic properties of glass forming pyranyliden derivatives in thin films

Organic solar cells based on solution processable materials could provide new low cost production method. Most popular materials are polymer P3HT and fullerene derivative PCBM. There is active study to find effective low molecular weight materials. Instead of planar structure, most of the research is made on bulk heterojunction samples as they are providing better efficiency. In our work we have studied three newly synthesized materials consisting 2-tert-butyl-6-methyl-4H-pyran-4-ylidene fragment. Each compound has different electron acceptor group. From photoconductivity experiments its threshold values were obtained. For photovoltaic experiments bulk heteroj unction samples containing investigated compounds mixed with PCBM were made. Best results with Incident Photon to Charge Carrier Efficiency (IPCE) larger than 0.4% at wavelength between 390 and 570 nm were obtained for system containing compound with malononitrile as electron acceptor group. Still, efficiency could be greatly improved as IPCE spectral dependence is not repeating absorption spectrum which show that generated charge carriers extraction from the sample was limited.