ORGANOTIN(IV)-PORPHINATE FOR PHOTOVOLTAIC BULK HETEROJUNCTIONS

Abstract

Due to the versatility and variability of their molecular structures, optical spectra, electrical properties, and supramolecular organization potential, porphyrins related compounds have been widely studied in organic solar cells [1,2]. Indeed, these applications are a natural function for these compounds, and they have been extensively investigated in a variety of formats including single molecules, macromolecular and supramolecular structures. In this work, poly(hexylthiophene) (P3HT) and organotin(IV)-[meso-tetra(4-carboxyphenyl) porphinate] have been employed for engineering planar and bulk heterojunctions by layer by layer deposition. Improving the overall efficiencies of photovoltaic devices requires the tuning of the HOMO-LUMO gap of the phthalocyanine or porphyrin phase to increase the spectral response while maintaining a sufficiently donor-to-acceptor LUMO offset to allow for high efficiency. In addition, engineering solar cells allowing for high hole and electron mobility requires the molecular and nanostructural control of both phases [3]. Here we investigate the employment of organotin(IV) moieties in the side chain of meso-tetra-carboxyphenylporphyrins with the specific aim to affect the electronic properties of porphyrins by modulating the molecular and supramolecular organization in thin film heterojunctions. In particular, by transferring these systems on ITO/PET substrates and by coupling them with polythiophene polymers we showed both in the planar and bulk heterojunction architectures interesting and modular fluorescence quenching due to an efficient electron transfer from the excited polythiophene to organotin(IV) porphyrin. The porphyrin organotin functions are put in relation with the supramolecular organization of the thin film along with the performance of plastic solar cell devices.