Many different organic solar cell structures are currently being studied worldwide, but the polymer donor/acceptor heterojunction solar cell is generally considered as the most promising approach. Largest advances in device performance have been brought about by improving the intermixing of the donor and acceptor materials, which promotes charge transfer and allows for efficient charge transport via the establishment of interpenetrating networks. In this paper, the advantages, disadvantages and the approaches to resolve the problems of polymer heterojunction solar cell were simply introduced; the mechanism was illustrated including the influence of the donor/acceptor ratio and the annealing on the charge generation, collection and recombination kinetics; novel low bandgap conductive polymers with the bandgap less than 1.8 eV were described in several aspects such as their design, the broadened absorption spectra; the applications of PCBM analogs, nanoscale inorganics, etc. as various highly efficient electron acceptor materials and the performance of their heterojunction solar cells were thoroughly narrated; the methods of modifying the nanoscale morphology of the photoactive layer consisted of using high boiling-point solvent and post-production treatments such as thermal annealing, applying electrical field and incorporating additives, which were all well expatiated; the research on the lifetime and degradation was summarized, and the enhanced stability by adding high Tg polymer was set forth; finally large-area processing and high efficiency of polymer heterojunction solar cells were expounded. (C) 2011 Elsevier B.V. All rights reserved.