Dr Matthew Griffith

© 2016 Elsevier B.V. All rights reserved. We demonstrate a pathway for fully roll-to-roll (R2R) prepared organic solar cells in a normal geometry with a R2R sputtered aluminium top electrode. Initial attempts utilizing a stack geometry without an electron transport layer (ETL) failed to obtain working devices. By applying aluminium zinc oxide (AZO) as an ETL, and optimizing the AZO thickness, working printed OPV devices with an efficiency of 0.58% were obtained. Further optimization of the donor:acceptor ratio in the active layer increased the efficiency to 0.90%. This work demonstrates that normal geometry organic solar cells using a metal top contact can be produced using large scale production techniques.

© 2015 IEEE. The potential for organic electronic technologies to produce low-cost energy at large scales is often cited as the most attractive feature of these materials. Such aspirations depend on the ability of materials to be printed from solution at high speeds across large areas using roll-to-roll (R2R) processing. However, progressing the technology from the laboratory environment into the industrial manufacturing arena is highly challenging. Closing the gap between exciting laboratory scale insights and the industrial scale potential requires a new focus on upscaling existing technology. Some recent progress in this area is discussed, concentrating on the need to pursue research across several different scales simultaneously in order to most effectively optimize large-scale fabrication efforts. These discussions are placed in the context of a design philosophy that combines printing, coating, and vacuum-based procedures. The challenges associated with selecting, and subsequently synthesizing, the optimal materials for device construction at large scales are considered. Case histories that highlight the unique challenges encountered during printing, coating, and sputtering at the R2R scale are presented. Developing testing and characterization procedures that can interrogate organic photovoltaic device (OPV) structures in real time is also discussed, and the opportunity for new tools to probe device photophysics is highlighted. The collection of innovative approaches to R2R fabrication challenges discussed here highlights the exciting progress toward efficient OPV modules becoming a commercial reality.

© 2016 The Royal Society of Chemistry. The synthesis and performance of a cost-effective mixed fullerene at the 100+ g scale with a reaction yield of 85% is demonstrated. The cost to convert a fullerene such as C60 into the mixed acceptor blend is less than $1 g-1. The photovoltaic performance of the mixed acceptor is demonstrated in both small scale and roll-to-roll printed devices.

© The Royal Society of Chemistry 2016. We investigate the suitability of four different inorganic materials (chromium oxide (CrOX), titanium oxide (TiOX), aluminium doped zinc oxide (AZO) and zinc oxide (ZnO)) as electrode transport layers in fully roll-to-roll (R2R) fabricated P3HT:ICxA organic solar cells. CrOX and TiOX were found to be unsuitable, as the CrOX devices did not exhibit rectifying behaviour while the TiOX devices did not withstand the annealing conditions. Of the last two ETLs, ZnO showed by far the most promise with devices demonstrating an average efficiency of 2.2%, which is the highest reported value for R2R devices in normal geometry, and a significantly extended lifetime compared with AZO devices under ISOS-L-2 conditions.

© 2015 American Chemical Society. A series of Zn(II) porphyrins which have asymmetrically substituted meso groups have been studied with UV-vis, resonance Raman, emission spectroscopies, and density functional theory (DFT) calculations. Dye-sensitized solar cells (DSSCs) of these materials have also been fabricated and their performance parameters measured. DFT calculations show perturbation of frontier molecular orbitals, and redox-active substituents cause greater perturbation than nonredox active substituents. All substituents cause a broadening of the B band, as is common for substituted porphyrins. TD-DFT calculations and resonance Raman spectroscopy suggest the donor and acceptor substituents play a small role in transitions of the B band. The meso donor substituent is electronically isolated and does not significantly perturb the molecular orbitals (MOs), while the meso cyanoacrylic acid TiO<inf>2</inf> binding group has a much larger effect on the e<inf>g</inf> MO in particular. However, in the oxidized porphyrin species, the hole is located on the meso substituent, localizing it away from the semiconductor surface, which should reduce recombination and also improve performance. They show modest efficiency when incorporated into solar cells; however, the pattern of behavior is consistent with localization of charge at the meso unit.

© the Partner Organisations 2014. The purpose of this work is to investigate the origin of improved photovoltaic performance of a series of di-chromophoric carbazole-substituted porphyrin dyes employed as sensitizers in dye-sensitized solar cells. Five di-chromophoric zinc porphyrin dyes with the same porphyrin core, a carbazole unit attached in the meso-position through a phenylethenyl linkage, and substituents spanning a range of electron affinities, in an attempt to tune the electronic level of the carbazole unit, have been synthesized (CZPs). Density functional theory (DFT) calculations predicted the nature of the electronic transitions observed in the CZP systems, showing a large degree of orbital mixing. In contrast, UV-vis absorption, resonance Raman spectroscopy and differential pulse voltammetry investigations suggested negligible interaction between the porphyrin and carbazole chromophores. Carbazole substitution led to a moderate increase in photon absorption intensity within the ~300 nm to 400 nm wavelength region, a smaller but broader Soret band absorption and slightly increased photon absorption intensity in the 550 nm to 650 nm Q band region. Despite the rather small changes in light harvesting and negligible changes in the HOMO/LUMO electronic levels, the photovoltaic performance of the new dyes is increased by as much as 30% compared to the single chromophore Zn porphyrin dye 5-(4-(2-cyano-2-carboxyethenyl)phenyl-15-phenyl-10,20-bis(2,4,6-trimethylphenyl)porphyrinato zinc(ii) (ZP1), leading to over 6% power conversion efficiencies (PCEs). Both open circuit voltage (VOC) and short circuit current (JSC) have increased. The increased VOC is attributed to increased electron lifetimes due to a steric blocking effect. Analysis of the increased short circuit current (¿JSC) showed that only less than 10% of ¿JSC originates from increased light absorption under simulated air mass 1.5 illumination, while the rest of the improvements are attributed to a steric effect enhancing the electron injection efficiency. These results suggest that developing non-conjugated multichromophoric dyes can lead to simultaneous increases in both the photocurrent and the photovoltage of dye-sensitized solar cells. This journal is

© 2014 AIP Publishing LLC. Here, we report the development of an organic thin film transistor (OTFT) based on printable solution processed polymers and employing a quantum tunnelling composite material as a sensor to convert the pressure wave output from detonation transmission tubing (shock tube) into an inherently amplified electronic signal for explosives initiation. The organic electronic detector allows detection of the signal in a low voltage operating range, an essential feature for sites employing live ordinances that is not provided by conventional electronic devices. We show that a 30-fold change in detector response is possible using the presented detector assembly. Degradation of the OTFT response with both time and repeated voltage scans was characterised, and device lifetime is shown to be consistent with the requirements for on-site printing and usage. The integration of a low cost organic electronic detector with inexpensive shock tube transmission fuse presents attractive avenues for the development of cheap and simple assemblies for precisely timed initiation of explosive chains.

Nanoparticulate zinc oxide can be prepared at low temperatures from solution processable zinc acetylacetonate. The use of this material as a cathode interfacial layer in nanoparticulate organic photovoltaic devices results in comparable performances to those based on reactive calcium layers. Importantly, the enhanced degradation stability and full solution processability make zinc oxide a more desirable material for the fabrication of large area printed devices. © 2014 AIP Publishing LLC.