Here we report the application of a conjugated copolymer based on thiophene and quinoxaline units, namely poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-altthiophene-2,5-diyl] (TQ1), to nanoparticle organic photovoltaics (NP-OPVs). TQ1 exhibits more desirable material properties for NP-OPV fabrication and operation, particularly a high glass transition temperature (T g) and amorphous nature, compared to the commonly applied semicrystalline polymer poly(3-hexylthiophene) (P3HT). This study reports the optimisation of TQ1:PC 71 BM (phenyl C 71 butyric acid methyl ester) NP-OPV device performance by the application of mild thermal annealing treatments in the range of the T g (sub-T g and post-T g), both in the active layer drying stages and post-cathode deposition annealing stages of device fabrication, and an in-depth study of the effect of these treatments on nanoparticle film morphology. In addition, we report a type of morphological evolution in nanoparticle films for OPV active layers that has not previously been observed, that of PC 71 BM nano-pathway formation between dispersed PC 71 BM-rich nanoparticle cores, which have the benefit of making the bulk film more conducive to charge percolation and extraction.

We present a simplified design for a scanning helium microscope (SHeM) which utilises almost entirely off the shelf components. The SHeM produces images by detecting scattered neutral helium atoms from a surface, forming an entirely surface sensitive and non-destructive imaging technique. This particular prototype instrument avoids the complexities of existing neutral atom optics by replacing them with an aperture in the form of an ion beam milled pinhole, resulting in a resolution of around 5 microns. Using the images so far produced, an initial investigation of topological contrast has been performed.

Delicate structures (such as biological samples, organic films for polymer electronics and adsorbate layers) suffer degradation under the energetic probes of traditional microscopies. Furthermore, the charged nature of these probes presents difficulties when imaging with electric or magnetic fields, or for insulating materials where the addition of a conductive coating is not desirable. Scanning helium microscopy is able to image such structures completely non-destructively by taking advantage of a neutral helium beam as a chemically, electrically and magnetically inert probe of the sample surface. Here we present scanning helium micrographs demonstrating image contrast arising from a range of mechanisms including, for the first time, chemical contrast observed from a series of metal–semiconductor interfaces. The ability of scanning helium microscopy to distinguish between materials without the risk of damage makes it ideal for investigating a wide range of systems.

Aqueous nanoparticle dispersions were prepared from a conjugated polymer poly(2,5-thiophene-alt-4,9-bis(2-hexyldecyl)-4,9-dihydrodithieno[3,2-c:3',2'-h][1,5]naphthyridine-5,10-dione) (PTNT) and fullerene blend utilizing chloroform as well as a non-chlorinated and environmentally benign solvent, o-xylene, as the miniemulsion dispersed phase solvent. The nanoparticles (NPs) in the solid-state film were found to coalesce and offered a smooth surface topography upon thermal annealing. Organic photovoltaics (OPVs) with photoactive layer processed from the nanoparticle dispersions prepared using chloroform as the miniemulsion dispersed phase solvent were found to have a power conversion efficiency M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT2 (PCE) of 1.04%, which increased to 1.65% for devices utilizing NPs prepared from o-xylene.Physical, thermal and optical properties of NPs prepared using both chloroform and o-xylene were systematically studied using dynamic mechanical thermal analysis (DMTA) and photoluminescence (PL) spectroscopy and correlated to their photovoltaic properties. The PL results indicate different morphology of NPs in the solid state were achieved by varying miniemulsion dispersed phase solvent.

Nanoparticle organic photovoltaics, a subfield of organic photovoltaics (OPV), has attracted increasing interest in recent years due to the eco-friendly fabrication of solar modules afforded by colloidal ink technology. Importantly, using this approach it is now possible to engineer the microstructure of the light absorbing/charge generating layer of organic photovoltaics; decoupling film morphology from film deposition. In this study, single-component nanoparticles of poly(3-hexylthiophene) (P3HT) and phenyl-C 61 butyric acid methyl ester (PC 61 BM) were synthesized and used to generate a two-phase microstructure with control over domain size prior to film deposition. Scanning transmission X-ray microscopy (STXM) and electron microscopy were used to characterize the thin film morphology. Uniquely, the measured microstructure was a direct input for a nanoscopic kinetic Monte Carlo (KMC) model allowing us to assess exciton transport properties that are experimentally inaccessible in these singlecomponent particles. Photoluminescence, UV−vis spectroscopy measurements, and KMC results of the nanoparticle thin films enabled the calculation of an experimental exciton dissociation efficiency (η ED) of 37% for the two-phase microstructure. The glass transition temperature (T g) of the materials was characterized with dynamic mechanical thermal analysis (DMTA) and thermal annealing led to an increase in η ED to 64% due to an increase in donor−acceptor interfaces in the thin film from both sintering of neighboring opposite-type particles in addition to the generation of a third mixed phase from diffusion of PC 61 BM into amorphous P3HT domains. As such, this study demonstrates the higher level of control over donor−acceptor film morphology enabled by customizing nanoparticulate colloidal inks, where the optimal three-phase film morphology for an OPV photoactive layer can be designed and engineered.

We present a scanning helium microscope equipped to make use of the unique contrast mechanisms, surface sensitivity, and zero damage imaging the technique affords. The new design delivers an order of magnitude increase in the available helium signal, yielding a higher contrast and signal-to-noise ratio. These improvements allow the microscope to produce high quality, intuitive images of samples using topological contrast, while setting the stage for investigations into further contrast mechanisms.

The scanning helium microscope (SHeM) is a new addition to the array of available microscopies, particularly for delicate materials that may suffer damage under techniques utilising light or charged particles. As with all other microscopies, the specifics of image formation within the instrument are required to gain a full understanding of the produced micrographs. We present work detailing the basics of the subject for the SHeM, including the specific nature of the projection distortions that arise due to the scattering geometry. Extension of these concepts allowed for an iterative ray tracing Monte Carlo model replicating diffuse scattering from a sample surface to be constructed. Comparisons between experimental data and simulations yielded a minimum resolvable step height of (67 ± 5) µm and a minimum resolvable planar angle of (4.3 ± 0.3)° for the instrument in question.

This work unravels the intricate relationship between non-fullerene acceptor material surface energy and nanostructure formation in organic nanoparticle colloids.