Selective photoresponse modification depending on the illumination energy of P3HT/TiO2 hybrid solar cells

ALEJANDRO KOFFMAN FRISCHKNECHT; EXEQUIEL YACUZZI; ROXANA COPPOLA; PLA JUAN CARLOS; MARÍA DOLORES PÉREZ

Colonia

Conferencia; Tenth International Conference on Electroluminescence and Optoelectronic Devices; 2014

Hybrid solar cells containing polymeric materials and metal oxides have received ample attention and many efforts have been dedicated to the understanding of the device operation. Ordered porous titania (p-TiO2) is believed to present optimum optical and electronic characteristics as the acceptor for well defined bulk heterojunction solar cells (BHJ) due to the rigidity and ease of preparation. Polymeric materials dissolved in common organic solvents can be easily infiltrated inside the titania pores as the donor material to complete the solid state hybrid device.1-3 In this work, we study devices fabricated by incorporating P3HT into the ordered pores of a sol-gel synthesized nanocrystalline titania. For the optimized devices we observe that the spectral response is modified upon illumination at different wavelengths, whereas the illuminated IV characteristics remain nearly unchanged. Upon UV irradiation (360 nm), the spectral response is drastically enhanced by almost 13% and slowly relaxes back to a lower response when the UV is turned off. Contrarily, when visible light (560 nm) reaches the device, the spectral response drops significantly to also relax back up to a value close to the original one when the visible light is blocked. This behavior was found to be reversible and repeatable within different devices. We observe that the 560 nm decay effect shows a lower characteristic time than the exponential raise found for the UV illuminated device. Deep, long lived electron traps have been described at the titania surface due to the presence of stable Ti(III)-OH states that populate upon UV light exposure.4-6 P3HT is mostly active in the visible region of the spectrum and therefore, illumination at 560 nm selectively targets the donor material. It is believed that interfacial P3HT excited states produce recombination of the titania trapped states, lowering the photocurrent. References (1) Coakley, K. M.; Liu, Y.; McGehee, M. D.; Frindell, K. L.; Stucky, G. D., Advanced Functional Materials 2003, 13, 301-306 (2) Coakley, K. M.; McGehee, M. D., Chem. Mater. 2004, 16, 4533-4542 (3) Wright, M.; Uddin, A., Solar Energy Materials and Solar Cells 2012, 107, 87-111 (4) Fujishima, A.; Zhang, X.; Tryk, D. A., Surface Science Reports 2008, 63, 515-582 (5) Pomoni, K.; Vomvas, A.; Trapalis, C., Thin Solid Films 2005, 479, 160-165 (6) Kim, J.; Kim, G.; Choi, Y.; Lee, J.; Heum Park, S.; Lee, K., Journal of Applied Physics 2012, 111, -