Morphology construction of vertical phase separation for large-area polymer solar cells.

Although the power conversion efficiency (PCE) of small-area polymer solar cells (PSCs) has now surpassed 10% upon various optimizations, it is still a challenge to improve the performance of large-area device partially due to the problems encountered in film morphology optimization and incompatibility of using these optimizations for size scale-up. Herein, we reported a method to effectively improve the morphology of photoactive layer and thus device efficiency under ambient atmosphere by using spray coating technique. It was found that by finely adjusting the parameters of the instrument, and the properties of the “electronic ink”, the dynamics of solvent evaporation after film deposition could be controlled. By resorting to a few techniques for morphology characterization, it confirmed that the resulting blend film showed desirable vertical phase separation where polymer enriched near the anode and PCBM adjacent to the cathode. The graded composition is beneficial for the efficient charge transportation as well as eventual charge collection. By using PBDT-TFQ/PC 71 BM composite as an example, the exceptional high PCEs of 4.6% and 4.1% were achieved for the devices with the size of 1.0 and 10.2 cm 2 , respectively. In comparison to conventional device fabrication process, this method is not only simple without additional treatment steps, but also dramatically increases the device efficiency, which opens a new way for fabricating highly efficient large-area PSCs. [ABSTRACT FROM AUTHOR]