Hybrid Bulk Heterojunction Solar Cells Based on P3HT and Porphyrin-Modified ZnO Nanorods

• Published in: Journal of physical chemistry. C Vol. 114; no. 25; pp. 11273 - 11278
• Main Authors: Said, A. J, Poize, G, Martini, C, Ferry, D, Marine, W, Giorgio, S, Fages, F, Hocq, J, Bouclé, J, Nelson, J, Durrant, J. R, Ackermann, J
• Format: Journal Article
• Language: English
• Published: American Chemical Society 01.07.2010
• Subjects: C: Energy Conversion and Storage
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp911125w

This work presents hybrid bulk heterojunction solar cells based on dye-sensitized zinc oxide (ZnO) nanorods blended with poly(3-hexylthiophene) (P3HT). Tetra(4-carboxyphenyl)porphyrin (TCPP) molecules were grafted onto the surface of ZnO nanorods to enlarge the absorption spectrum of the blend. We demonstrate that additional bands in the external quantum efficiency (EQE) spectra corresponding to Soret and Q-band absorption can already been observed at very low dye concentration at the ZnO surface. Therefore, direct grafting of TCPP onto ZnO nanorods leads to very efficient electron injection process into the ZnO nanorods after the light absorption of the dye. However, the overall photocurrent of the devices decreases gradually with TCPP concentration at the ZnO nanorod surface. The recombination dynamics of the photogenerated charges at the P3HT:ZnO interface are investigated by transient absorption spectroscopy on micro- to millisecond time scales. We observe that the lifetime of the P3HT polarons is reduced by an order of magnitude by grafting TCPP of already low concentration at the ZnO surface. Furthermore, high-resolution transmission electronic microscopy analysis of the blend morphology reveals that aggregation of ZnO nanorods within the P3HT is strongly increased by TCPP grafting. Therefore, we conclude that TCPP grafting is beneficial for additional photocurrent generation in the P3HT:ZnO blend but introduces strong modification of the blend morphology and charge carrier dynamics at the P3HT/ZnO interface, which finally reduces the overall photocurrent generation.