Donal Bradley

Abstract:

Exploring long-range electron transport across protein assemblies is a central interest in both the fundamental research of biological processes and the emerging field of bioelectronics. This work examines the use of serum-albumin-based freestanding mats as macroscopic electron mediators in bioelectronic devices. In particular, this study focuses on how doping the protein mat with hemin improves charge-transport. It is demonstrated that doping can increase conductivity 40-fold via electron hopping between adjacent hemin molecules, resulting in the highest measured conductance for a protein-based material yet reported, and transport over centimeter length scales. The use of distance-dependent AC impedance and DC current-voltage measurements allows the contribution from electron hopping between adjacent hemin molecules to be isolated. Because the hemin-doped serum albumin mats have both biocompatibility and fabrication simplicity, they should be applicable to a range of bioelectronic devices of varying sizes, configurations, and applications.

Abstract:

In order to investigate the solid-state light emission of zinc salphen macrocycle complexes, 7 dinuclear zinc salphen macrocycle complexes (1-7), with acetate or hexanoate coligands, are synthesized. The complexes are stable in air up to 300 °C, as shown via thermogravimetric analysis (TGA), and exhibit green to orange-red emission in solution (λem = 550-600 nm, PLQE ≤ 1%) and slightly enhanced yellow to orange-red emission in the solid state (λem = 570-625 nm, PLQE = 1-5%). Complexes 1, 2, 4, 5, and 7 also display aggregation-induced enhanced emission (AIEE) when hexane (a nonsolvent) is added to a chloroform solution of the complexes, with complex 4 displaying a 75-fold increase in peak emission intensity upon aggregation (in 0.25:0.75 chloroform:hexane mixture).

Abstract:

High power conversion efficiency (PCE) inverted organic photovoltaics (OPVs) usually use thermally evaporated MoO3 as a hole transporting layer (HTL). Despite the high PCE values reported, stability investigations are still limited and the exact degradation mechanisms of inverted OPVs using thermally evaporated MoO3 HTL remain unclear under different environmental stress factors. In this study, we monitor the accelerated lifetime performance under the ISOS-D-2 protocol (heat conditions 65 °C) of nonencapsulated inverted OPVs based on the thiophene-based active layer materials poly(3-hexylthiophene) (P3HT), poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7), and thieno[3,2-b]thiophene-diketopyrrolopyrrole (DPPTTT) blended with [6,6]-phenyl C71-butyric acid methyl ester (PC[70]BM). The presented investigation of degradation mechanisms focus on optimized P3HT:PC[70]BM-based inverted OPVs. Specifically, we present a systematic study on the thermal stability of inverted P3HT:PC[70]BM OPVs using solution-processed poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and evaporated MoO3 HTL. Using a series of measurements and reverse engineering methods, we report that the P3HT:PC[70]BM/MoO3 interface is the main origin of failure of the P3HT:PC[70]BM-based inverted OPVs under intense heat conditions, a trend that is also observed for the other two thiophene-based polymers used in this study.

Abstract:

Here we demonstrate deep red light-sensing all-polymer phototransistors with bulk heterojunction layers of poly[4,8-bis[(2-ethylhexyl)-oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]-thiophenediyl] (PTB7) and poly[[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)] (P(NDI2OD-T2)). The device performances were investigated by varying the incident light intensity of the deep red light (675 nm), while the signal amplification capability was examined by changing the gate and drain voltages. The result showed that the present all-polymer phototransistors exhibited higher photoresponsivity (∼14 A/W) and better on/off photoswitching characteristics than the devices with the pristine polymers under illumination with the deep red light. The enhanced phototransistor performances were attributed to the well-aligned nanofiber-like morphology and nanocrystalline P(NDI2OD-T2) domains in the blend films, which are beneficial for charge separation and charge transport in the in-plane direction.