ИСТИНА

The most efficient polymer solar cells are based on bulk heterojunction (BHJ), formed by interpenetrating phases of a conjugated polymer as electron donor and a fullerene derivative as electron acceptor. Recent advances in polymer-fullerene solar cells are mainly due to the development of new donor components, while as acceptor only a few fullerene derivatives such as PCBM are successful. The most attempts to use novel fullerene derivatives in BHJ have not led to increase in the polymer solar cell performance. It is known that power conversion efficiency (PCE) of bilayer organic solar cells based on pristine C60 with aluminum cathode enhances dramatically, when the buffer layer of bathocuproine (BCP) is introduced between C60 and cathode. One can suggest that the poor contact between fullerene and the metal electrode is one of the reasons for low PCE of organic solar cells based on new fullerene derivatives. We suggest that success of PCBM is due to the presence of carboxylic group, which could form complexes with metal atoms and prevent their diffusion into active layer. To substantiate our suggestion, we fabricated devices based on different fullerene derivatives acceptor: widely studied PCBM, and several novel fullerene derivatives. For solar cells, based on latter, introduction of BCP layer enhanced the open-circuit voltage (Voc) twice, while for PCBM-based cell the effect of BCP is not so high. The roles of BCP layer in Voc increase of polymer solar cells based on PCBM either novel fullerene derivatives are discussed.