Combinative Effect of Additive and Thermal Annealing Processes Delivers High Efficiency All-Polymer Solar Cells

The combinative effects of thermal annealing and additive processes on the performance of all-polymer bulk heterojunction (BHJ) solar cells with composites of different donor polymers (PTQ1, P3HT, PTB7-Th) and poly[1,8-bis(dicarboximide)-2,6-diyl]- alt -5,5′-(2,2′-bithiophene)P(NDI2OD-T2) [PolyeraActivInk N2200] were investigated. We found that devices treated with both processes show significant improved performance compared with those treated with either process alone. To reveal the mechanism of this enhancement in device performance, the optical and electrical properties of all-polymer blends were carefully investigated in the PTQ1/N2200 system. The synergetic effect of both processes can largely enhance the polymer aggregation, especially for N2200, leading to improved absorbance, improved charge mobility, and thus higher device performance. In addition, the device efficiency can be further enhanced by postannealing which can improve the interface between the active layer and Al cathode, as revealed by atomic force microscopy investigations. Moreover, the approaches reported here provide a simple and versatile method to optimize all-polymer solar cells and may help pave the route for this emerging system to overtake the state-of-the-art polymer/fullerene solar cells.