18.4 % Organic Solar Cells Using a High Ionization Energy Self‐Assembled Monolayer as Hole‐Extraction Interlayer

Self-assembled monolayers (SAMs) based on Br-2PACz ([2-(3,6-dibromo-9H-carbazol-9-yl)ethyl]phosphonic acid) 2PACz ([2-(9H-Carbazol-9-yl)ethyl]phosphonic and MeO-2PACz ([2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic molecules were investigated as hole-extracting interlayers in organic photovoltaics (OPVs). The highest occupied molecular orbital (HOMO) energies of these SAMs measured at −6.01 −5.30 eV for MeO-2PACz, respectively, found to induce significant changes the work function (WF) indium-tin-oxide (ITO) electrodes upon chemical functionalization. OPV cells PM6 (poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo[1,2-b:4,5-b’]dithiophene))-alt-(5,5-(1’,3’-di-2-thienyl-5’,7’-bis(2-ethylhexyl)benzo[1’,2’-c:4’,5’-c’]dithiophene-4,8-dione)]) : BTP-eC9 PC71BM ([6,6]-phenyl-C71-butyric acid methyl ester) using ITO/Br-2PACz anodes exhibited a maximum power conversion efficiency (PCE) 18.4 %, outperforming devices with ITO/MeO-2PACz (14.5 %) ITO/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT PSS) (17.5 %). higher PCE was originate from much WF (−5.81 eV) compared (4.58 ITO/PEDOT PSS (4.9 eV), resulting lower interface resistance, improved hole transport/extraction, trap-assisted recombination, longer carrier lifetimes. Importantly, electrode chemically stable, after removal SAM it could be recycled reused construct fresh OPVs equally impressive performance.