Annealing Controls Ultrafast Dynamics of Carrier Production in Organic Photovoltaics Incorporating a Nonfullerene Acceptor

Abstract

Nonfullerene acceptors have emerged as leading candidates in organic photovoltaics pushing past some of the limitations of their fullerene counterparts with absorption extending in the visible and NIR, decreased air-sensitivity, and tunable energy levels. Significant progress has been made in demonstrating the potential of nonfullerene acceptor-based devices to reach high efficiencies; however, a photophysical and mechanistic understanding of charge generation in these nonfullerene acceptors lags behind. In particular, the effects of annealing on carrier production have not been previously examined. Here, we use transient absorption spectroscopy and atomic force microscopy to examine the effect of solvent vapor annealing on a perylene diimide-based nonfullerene acceptor, PDI-DPP-PDI. We find that when mixed with the donor PTB7-Th, the effect of solvent vapor annealing on PDI-DPP-PDI is to reduce geminate recombination, leading to balanced exciton generation and charge separation.

Perylene-diimide for organic solar cells: current scenario and prospects in molecular geometric, functionalization, and optoelectronic properties

“…[141][142][143] To enhance stacking and/or prevent severe aggregation, several linkers were synthesized between the dimers of PDI in the small molecules based on PDI. [144][145][146] It is common practice to bind a large number of PDIs together using electron-rich linkers to construct a twisted acceptordonor-acceptor (A-D-A) molecule, which is done to increase the device's overall efficiency. Using molecular features, such as bonding, lms can be designed and made with different structures.…”