Ben Vaughan

Combining Printing, Coating, and Vacuum Deposition on the Roll-to-Roll Scale: A Hybrid Organic Photovoltaics Fabrication

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.

A low-cost mixed fullerene acceptor blend for printed electronics

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

Effect of a calcium cathode on water-based nanoparticulate solar cells

1 g−1. The photovoltaic performance of the mixed acceptor is demonstrated in both small scale and roll-to-roll printed devices.

Solution processable interface materials for nanoparticulate organic photovoltaic devices

Water-based nanoparticulate (NP) and bulk heterojunction (BHJ) organic photovoltaic (OPV) devices based on blends of poly(9,9-dioctylfluorene-co-N,N-bis(4-butylphenyl)-N,Ndiphenyl-1,4-phenylenediamine) (PFB) and poly(9,9-dioctylfluorene-co-benzothiadiazole (F8BT) have been fabricated with aluminium and calcium/aluminium cathodes. The NP devices exhibit power conversion efficiencies (PCEs) that are double that of the corresponding BHJ device. Moreover, the addition of calcium into the cathode structure results in a dramatic increase in open circuit voltage and PCEs approaching 1% for water-based polyfluorene OPV devices.

Low resistance TiO 2 -passivated calcium contacts to for crystalline silicon solar cells

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.

Comparison of inorganic electron transport layers in fully roll-to-roll coated/printed organic photovoltaics in normal geometry

It has recently been shown that low resistance Ohmic contact to lightly doped n-type crystalline silicon (c-Si) is possible by direct metallization via a thin layer of the low work function metal calcium (φ ~2.9 eV) and an overlying aluminium capping layer. Using this approach upper limit contact resistivities of <; 2 mΩcm2 can be realised on undiffused n-type surfaces. However, recombination at the Ca / Si interface limits the application of the Ca contact to very low contact fractions which leads to non-negligible resistive losses and an increase in device fabrication complexity. Here we show that the low resistance Ohmic contact of the Ca / Al structure is retained after the addition of a TiO2 interlayer, leading the way to the development of a passivated contact device utilizing TiO2 and Ca.

Comparing model parameters of bulk heterojunction and nanoparticulate photovoltaic cells using a two-diode model

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.

Vertical Stratification and Interfacial Structure in P3HT:PCBM Organic Solar Cells

The performance of organic solar cells can be influenced by many factors such as device structure, active layer morphology, and active layer material. These performance differences can be seen through their characteristic electrical parameters. The aim of this article is to show the differences in electrical parameter properties that result from differences in active layer morphology. In particular, the differences between bulk heterojunction (BHJ) and nanoparticulate solar cells are determined using a two‐diode circuit model. The simulation results show clear differences in photocurrent generation, serial resistance, and shunt resistance between the bulk heterojunction and nanoparticulate photovoltaic cells.