Investigation of donor-acceptor molecular and quantum dot layer systems by surface photo-voltage techniques

TH. DITTRICH, S. FENGLER, E. ZILLNER, J. RAPPICH, X. ZHANG, L. OTERO, F. FUNGO, L. MACOR, M. GERVALDO, D. HEREDIA, C.-Y. LIN, L.-C. CHI, C. FANG, S.-W. LII, K.-T. WONG

Encuentro; XI encuentro latinoamericano de fotoquímica y fotobiología; 2012

Donor-acceptor molecule and quantum dot (QD) layer systems are of great interest for applications in optoelectronics, photovoltaics and photocatalysis due to their potential for engineering of optical and surface electronic properties. For example, dye sensitized solar cells were realized with donor-acceptor spiro compounds [1] and hetero-junctions between TiO2 and PbS based QD layers are suitable for efficient QD solar cells [2]. Spectral and time dependent surface photovoltage (SPV) techniques were used to study processes of charge separation across interfaces in layer systems containing donor-acceptor spiro compounds with dicyano or cyanoacrylic acceptor and diphenylamine donor groups [3] or containing CdSe QDs with TOP/OA, pyridine or dithiol surfactants [4,5]. Layers were prepared by dip coating or electrochemically. Intramolecular charge transfer and charge separation by electron injection were distinguished. Results were interpreted from point of view of directed molecule adsorption. A strong influence of the donor group on charge separation was observed. It was shown that the adsorption dependence of optical transitions of donor-acceptor spiro compounds can be well studied by SPV. It was found that electronic defect states at QD surfaces are generated by successive surfactant exchange. Information about the energetic distribution and density of defect states at surfaces of QDs was obtained by random walk simulations of SPV transients within the frame of an isolated QD approximation.