Electroabsorption and Oppositely Directed Built-in Fields in a Photovoltaic Organic Heterostructure

摘要

The directions and intensities of local electric fields spontaneously built into organic nanoscale structures of Schottky-diode type, indium tin oxide (ITO)–CuPc–Al and ITO–C_(60)–Al, with donor and acceptor layers of copper phthalocyanine (CuPc) and fullerene (C_(60)) have been investigated using an improved spectral electroabsorption technique. It is established that, in the absence of external field and illumination, the built-in fields in the bulk of these structures are directed differently: from Al to ITO in the case of CuPc and from ITO to Al in the case of C_(60). The best studied photovoltaic heterostructure ITO–CuPc– C_(60)–Al contains simultaneously strong built-in fields in CuPc and C60 layers, with strengths of about 15 and –22 V/μm, respectively. A high (on the order of 10~(-3) C/m~2) positive space charge arises at the donor–acceptor interface, and the oppositely directed fields may either increase or reduce the efficiency of light–energy converters, depending on the heterostructure parameters.