ABSTRACT
Polymer solar cells (PSCs) have been attracting considerable attention as a promising renewable energy source owing to their unique advantage of light weight, low cost, high flexibility, and easy roll-to-roll fabrication.1-4 Since Yu et al. first reported a poly[2methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV):[6,6]-phenyl-C61butyric acid methyl ester (PC61BM) bulk heterojunction (BHJ) PSC structure in 1995,5 significant progress in BHJ-PSC technology has been achieved.5 During the past decade, the power conversion efficiency (PCE) of the champion small-area PSCs has been dramatically improved to 10.6%.6-11 For PSCs, BHJ structure plays a determinative role in all of the major photoelectric conversion processes, including charge separation, which relies on effective donor/acceptor interfaces; charge transport, which is critically determined by the morphology of the thin film; and charge extraction, which can only occur at high-quality interfaces between donor(acceptor)/electrodes. In order to improve PCE of BHJ-PSCs so as to meet the requirement for commercial applications, a balanced consideration of photocurrent, photovoltage, and fill factor (FF), which are determined by the photoactive materials12,13 and device architectures,14-16 needs to be implemented.
