| First, an investigation of anode/active layer interface modification in bulk-heterojunction organic photovoltaics (OPVs) is carried out using poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) and/or a hole transporting/electron-blocking blend of 4,4'-bis[(p-trichlorosilylpropylphenyl)-phenylamino]biphenyl (TPDSi2) and poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] (TFB). Current--voltage scans in AM 1.5G light and dark and impedance spectroscopy in the dark show the TPDSi2:TFB blend produces MDMO-PPV: PCBM OPVs with increased open-circuit voltage (Voc), power conversion efficiency, thermal stability, and mean charge carrier lifetime compared to devices with no interfacial layer (IFL) or with PEDOT:PSS. Using PEDOT:PSS and TPDSi2:TFB together in the same cell greatly reduces dark current, further increases carrier lifetime, and produces the highest Voc (0.91 V) by combining the electron-blocking effects of both layers.;Next, the ITO anode pre-treatment was investigated by X-ray photoelectron spectroscopy to understand why oxygen plasma, UV ozone, and solvent cleaning markedly affect cell response in combination with each IFL. The O2 plasma and UV ozone treatment (30 min) most effectively clean the ITO surface and are the best methods to prepare the surface for PEDOT:PSS deposition; UV ozone (5 min) produces optimum solar cells fabricated with a TPDSi2:TFB IFL; and solvent cleaning leaves significant residual carbon contamination on the ITO and is best followed by an additional O2 plasma or UV ozone treatment.;Finally, the design, synthesis, characterization, and device implementation of a novel IFL component in BHJ OPV cells using poly(3-hexylthiophene) (P3HT) as the donor polymer and PCBM as the acceptor. The IFL precursor, 5,5'-bis[( p-trichlorosilylpropylphenyl)phenylamino]-2,2'-bithiophene (PABTSi2), substitutes a bithiophene moiety in place of the biphenyl core of the proven IFL precursor, TPDSi2, with the intention of increasing electron-density and raising the HOMO energy to that of P3HT (∼5.0 eV). The synthesis and subsequent electrochemical analysis of PABTSi 2 indicates a HOMO energy of 4.9 eV, while the LUMO level remains sufficiently high, at 2.2 eV, to effectively block electrons from recombining with holes at the cell ITO anode. P3HT:PCBM devices utilizing a crosslinking, insoluble IFL consisting of a 1:2 blend of PABTSi2 and TFB, spin-coated from chlorobenzene, exhibit a power conversion efficiency of 3.24%. |
