Novel Nonconjugated Polymer as Cathode Buffer Layer for Efficient Organic Solar Cells.

A novel nonconjugated polymer named poly(2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt) (PAMPS-Na) was designed and synthesized. The PAMPS-Na has good solubility in polar solvents, such as water, methanol, and ethanol, which can be used as the cathode buffer layer in organic solar cells (OSCs) through solution processing without damaging the underlying active layer. Moreover, it was found that PAMPS-Na can significantly decrease the Al work function when it was modified with Al. To reveal its universal application in organic photovoltaic devices, a variety of photovoltaic donor materials, including two medium-band gap polymers, a wide-band gap polymer, and a small molecule donor were employed to fabricate OSCs. Compared with OSCs with Ca/Al electrode, the devices based on PAMPS-Na/Al exhibited higher photovoltaic performance, mainly because of the increased short-circuit current. Additionally, OSCs with PAMPS-Na/Al displayed better ambient stability than devices with Ca/Al. It is also interesting to find that the performance of the devices can tolerate a wide change of PAMPS-Na's thickness, enabling the potential for large-scale fabrication of OSCs. The results suggest that PAMPS-Na is a promising candidate as the cathode buffer layer to improve the efficiency and stability of OSCs.