New advances in non-fullerene acceptor based organic solar cells

Non-fullerene organic solar cells (NF-OSCs), in which an n-type organic molecule instead of a fullerene derivative is utilized as the electron-acceptor material, have recently emerged as a new topic in the field of organic solar cells. Replacement of the traditional fullerene acceptor in the photoactive layer of a normal organic solar cell with the organic acceptor gives rise to several advantages, like light absorption and energy level tunability, diversity of donor-to-acceptor combination, and large-scale production of acceptor materials. Studies on NF-OSCs can be traced back to 1986, when the first bilayered organic solar cell was proposed. Unfortunately, they has been advancing very slowly and the power-conversion-efficiency (PCE) was only approaching or exceeding 2% up to 2012. Fast advances have been driven forward since 2013, when the PCE value first broke through 4%, and the reported PCE value has now reached about 8% after a short period of 3 years. If we turn to natural systems such as the photosynthesis systems I and II, in which Nature utilizes organic molecules to accomplish high-efficiency solar-to-chemical energy conversion through the cascade unidirectional electron-hole transfer paths, we can rationally expect an even higher PCE and a convincing future for NF-OSCs. In this review, we will address recent new progress in this sub-branch of organic solar cells.