Fine-Tuning Donor Material Deposition with Ultrasonic Aerosol Jet Printing to Balance Efficiency and Stability in Inverted Organic Photovoltaic Devices.

The response surface methodology (RSM) based on a Box-Behnken (BB) design of experiment (DoE) approach was performed, with the central point repeated four times to enhance statistical reliability, to systematically investigate the influence of ultrasonic aerosol jet printing (uAJP) parameters such as speed, flow, and power, while depositing the donor material deposition, on the acceptor/donor ratio and power conversion efficiency (PCE). Efforts were made to tune the D:A ratio to approximately 1:1.2, a composition widely used for the PM6:Y12 active layer system. Despite the sequential deposition of the donor material onto the acceptor, the resulting active layer exhibited a bulk heterojunction (BHJ) morphology rather than a layer-by-layer (LbL) structure. Further analysis such as film-depth-dependent light absorption spectra (FLAS) and cross section of the electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) or STEM-EELS was used to explore the interplay between deposition parameters and vertical blending behavior in the active layer. Finally, we evaluated the stability of these OPV devices under continuous one-sun illumination for 1080 h, revealing that the most efficient devices also exhibited the highest operational stability.