Stability of nonfullerene organic solar cells

Remarkable progress has been observed over the last decade in the development of solution-processable organic solar cells (OSCs) made with different polymer donor- /fullerene-blend systems. Fullerene-based acceptors have some limitations with respect to cell performance improvement because of their weak light absorption, limited energy level tuning, and challenging purification process. Therefore, the development of nonfullerene acceptor materials has attracted increasing attention for application to OSCs because of their advantages of tunable electronic properties, high absorption characteristics, low lowest unoccupied molecular orbital and highest occupied molecular orbital energy levels, and solution-fabrication capability for large-area low-cost flexible OSCs. However, the fundamental understanding of the effects of morphology and vertical stratification of bulk heterojunction (BHJ) on charge transfer, charge recombination processes, power conversion efficiency and the stability of nonfullerene OSCs have not yet been systemically studied.

We propose to unravel the origin of the efficient operation of nonfullerene OSCs by using newly developed polymer/nonfullerene blend systems. The role of the morphology and the vertical stratification of BHJ in the device design will be examined using the grazing-incidence small-angle X-ray scattering and wide-angle X-ray scattering, X- ray photoelectron spectroscopy, and atomic force microscopy. The effects of a buildup of space charges, charge extraction, and bimolecular recombination processes on the performance and the stability of nonfullerene OSCs will be analyzed using space charge- limited current and photo-physics measurement techniques. The accomplishment of the proposed project will have a profound impact on the development of high-performance solution-processable nonfullerene OSCs.