Surface properties of buffer layers affect the performance of PM6:Y6–based organic photovoltaics

Abstract In this study we used p-type [poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) and nickel oxide] and n-type (sol–gel and nanoparticle zinc oxides) materials as transporting layers for PM6:Y6–based organic photovoltaic (OPV) devices. These solution-processed transporting layers exhibited various surface energies, morphologies, and roughnesses that affected the subsequent growth of PM6:Y6 blend films. Using atomic force microscopy and grazing-incidence wide-angle X-ray spectroscopy, we observed various PM6:Y6 blend film morphologies on the different substrates. Furthermore, the surface-induced PM6:Y6 blend morphology influenced the mechanism of carrier recombination and, thereby, affected the device performance. Among our tested systems, the PEDOT:PSS–based devices exhibited superior surface properties, possessed larger phase-segregated domains, and featured strong molecular packing, all of which resulted in OPVs displaying power conversion efficiencies (PCEs) of up to 11.5%. When incorporating 1-chloronaphthalene as an additive during solution processing, the molecular packing was enhanced, thereby improving the PCE of the resulting devices from 11.5 to 13.4%. Devices incorporating ZnO (sol–gel) displayed performance comparable with that of the PEDOT:PSS–based devices, but exhibited superior air stability without encapsulation (25 °C, 40% humidity).