Naphthalene as a Thermal-Annealing-Free Volatile Solid Additive in Non-Fullerene Polymer Solar Cells with Improved Performance and Reproducibility

Abstract

Highly volatile solid additives have attracted much attention recently because they enhance molecular packing order and possibly solve the problems of poor reproducibility and instability of polymer solar cells (PSCs) with solvent additives. The shortcoming is that existing solid additives require thermal annealing (TA) to remove them from the active layer, leading to an increase in the complexity of the device fabrication process and morphology rearrangement problems. This study introduces a commercially available, low-cost, and highly volatile material, naphthalene (NA), as a solid additive used in PSCs based on PM6: Y6. NA is well mixed with a non-fullerene acceptor and can restrict excessive aggregation of the donor and acceptor, producing efficiencies comparable to PSCs processed by 1-chloronaphthalene (CN) solvent additive. As a result, a maximum power conversion efficiency (PCE) of 16.52% for NA-processed PSC is achieved, higher than that of a PCE of 16.07% for CN-processed PSC with TA. NA-processed PSCs exhibit comparable efficiencies (PCE of 16.10%) without TA treatment and higher reproducibility/stability than CN-processed PSCs. This study demonstrates a low-cost and excellent volatile solid additive to improve the device performance and the potential for exploring new solid additives that can readily be made volatile without TA.