LAUSR

Here we report that ultrathin polymeric films doped with organic acid molecules can act as an electron-transporting interfacial layer in polymer:nonfullerene solar cells. The polymeric interfacial layers, which consist of poly(ethylene imine) (PEI) doped with 3-hydroxypropane-1-sulfonic acid (HPSA) at various HPSA molar ratios, were introduced between transparent indium-tin oxide (ITO) electrodes and polymer:nonfullerene bulk heterojunction (BHJ) layers. The HPSA-doped PEI (PEI:HPSA) films were optically translucent in the wavelength range of 300 ∼ 800 nm, while the acidity of PEI solutions reached ca. pH = 7 at HPSA = 30 mol%. The power conversion efficiency of solar cells was improved by doping 20 mol% HPSA due to the increased short circuit current density without open circuit voltage reduction. The improvement in solar cell performances has been attributed to an adequate control of HPSA doping ratios, which spares undoped amine units of PEI for making sufficient net dipole layers with ITO surfaces and makes permanent charges for high electrical conductivity in the layers. The surface morphology and doped states were characterized with atomic force microscopy and X-ray photoelectron spectroscopy. This article is protected by copyright. All rights reserved.