Molecular Design, Characterization, and Implementation of Organic Semiconducting Oligothiophenes

This work describes new self-assembly strategies and realizes new directions for rational side chain design in organic semiconductors. I examined the synthesis and structure property relations of monomers and dimers of a benchmark organic semiconductor system using a variety of linear alkyl side chains. I observed critical onsets for packing trends based on alkyl side chain length in both monomers and dimers. Monomer systems exhibited a pronounced even-odd effect manifesting directly from side chain length. In the dimer systems, I observed spontaneous bimolecular crystal formation with PC61BM which undergoes an order-to-disorder transition at small side chain lengths. Combining these systematic structure-property studies, I designed and synthesized a set of BTTT dimers with variable substitution of long and short side chains. These systems displayed solid-state packing behaviors unique to their side chain pattern, both in neat films and in blends with fullerene derivatives. As these oligomers provide excellent model systems for their polymer analogues, the translation of the structure-property lessons here will benefit small molecule systems and polymer systems alike. More broadly, this work identifies the utility and application of variable substitution for imparting order and ‘smart’ self-assembly in organic semicondutors or other organic crystalline materials

Impact of morphology on polaron delocalization in a semicrystalline conjugated polymer

We investigate the delocalization of holes in the semicrystalline conjugated polymer poly(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene) (PBTTT) by directly measuring the hyperfine coupling between photogenerated polarons and bound nuclear spins using electron nuclear double resonance spectroscopy. An extrapolation of the corresponding oligomer spectra reveals that charges tend to delocalize over 4.0–4.8 nm with delocalization strongly dependent on molecular order and crystallinity of the PBTTT polymer thin films. Density functional theory calculations of hyperfine couplings confirm that long-range corrected functionals appropriately describe the change in coupling strength with increasing oligomer size and agree well with the experimentally measured polymer limit. Our discussion presents general guidelines illustrating the various pitfalls and opportunities when deducing polaron localization lengths from hyperfine coupling spectra of conjugated polymers

Effect of alkyl chain length on the properties of triphenylamine-based hole transport materials and their performance in perovskite solar cells

A new series of diacetylide-triphenylamine (DATPA) derivatives with five different alkyl chains in the para position, MeO, EtO, nPrO, iPrO and BuO, were synthesised, fully characterised and their function as hole-transport materials in perovskite solar cells (PSC) studied. Their thermal, optical and electrochemical properties were investigated along with their molecular packing and charge transport properties to analyse the influence of different alkyl chains in the solar cell parameters. The shorter alkyl chain facilitates more compact packing structures which enhanced the hole mobilities and reduced recombination. This work suggests that the molecule with the methoxy substituent (MeO) exhibits the best semiconductive properties with a power conversion efficiency of up to 5.63%, an open circuit voltage (Voc) of 0.83 V, a photocurrent density (Jsc) of 10.84 mA cm−2 and a fill factor of 62.3% in perovskite solar cells. Upon replacing the methoxy group with longer alkyl chain substituents without changing the energy levels, there is a decrease in the charge mobility as well as PCE (e.g. 3.29% for BuO-DATPA). The alkyl chain length of semiconductive molecules plays an important role in achieving high performance perovskite solar cells

Wingspan

As a young boy, Ken Boyd \u2761 fell in love with flying. Now retired, he\u27s returned to the skies in his own hand-crafted plane

Molecular Design, Characterization, and Implementation of Organic Semiconducting Oligothiophenes

This work describes new self-assembly strategies and realizes new directions for rational side chain design in organic semiconductors. I examined the synthesis and structure property relations of monomers and dimers of a benchmark organic semiconductor system using a variety of linear alkyl side chains. I observed critical onsets for packing trends based on alkyl side chain length in both monomers and dimers. Monomer systems exhibited a pronounced even-odd effect manifesting directly from side chain length. In the dimer systems, I observed spontaneous bimolecular crystal formation with PC61BM which undergoes an order-to-disorder transition at small side chain lengths. Combining these systematic structure-property studies, I designed and synthesized a set of BTTT dimers with variable substitution of long and short side chains. These systems displayed solid-state packing behaviors unique to their side chain pattern, both in neat films and in blends with fullerene derivatives. As these oligomers provide excellent model systems for their polymer analogues, the translation of the structure-property lessons here will benefit small molecule systems and polymer systems alike. More broadly, this work identifies the utility and application of variable substitution for imparting order and ‘smart’ self-assembly in organic semicondutors or other organic crystalline materials.Polymer Science and EngineeringDoctor of Philosophy (PhD

Impact of morphology on polaron delocalization in a semicrystalline conjugated polymer

We use spin resonant techniques to shed light on the delocalization length of polarons in a semicrystalline conjugated polymer and reveal how it directly depends on the thin film morphology.</p