Lead-free piezoelectric composites with polymeric matrices offer a scalable and eco-friendly solution to sensing and energy harvesting applications. Piezoelectric polymers such as PVDF are particularly interesting because of the possibility to engineer the performance of these materials through addition of higher-performance piezoelectric inclusions and nanomaterials and to scalably manufacture such composites by emerging techniques such as 3D printing. This work makes two contributions, namely towards composite design and towards development of accurate effective property models. In the context of composite design, we evaluate the piezoelectric performance of PVDF modified by the addition of polycrystalline-BaTiO 3 and multiwalled carbon nanotubes. Firstly, the addition of BaTiO 3 dramatically improves the electric field within the composite offering significant advantages specially at low BaTiO 3 concentrations. Secondly, the addition of carbon nanotubes to the matrix, particularly at higher BaTiO 3 loadings, leads to an order of magnitude increase in the piezoelectric flux generation. Further enhancement in the flux generation is also possible by tuning the polycrystallinity of the BaTiO 3 inclusions. However, these behaviours are inclusion-driven and the piezoelectric behaviour of the matrix does not contribute to this improvement. Importantly, a small addition of BaTiO 3 and CNT into the PVDF matrix, away from percolation, can simultaneously improve flux and electric field generation. In this part of the work, we assume an isotropic PVDF matrix. Given that PVDF is elastically anisotropic, the second aspect of this work is the development of an effective property model for CNTmodified PVDF, taking into account the elastic anisotropy of poled PVDF, to predict the elastic coefficients of CNT-modified PVDF matrices, thus undertaking a key step towards modelling anisotropic piezoelectric composites. We show that the anisotropy-based model makes similar predictions in the effective composite behaviour, indicating that in the case of Smart Materials and Structures

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Photonic architectures in optoelectronic devices are comprised of uniform periodic structural arrangement which aids in improved interaction with light. The processing of such photonic arrays generally involves several steps of fabrication. This work proposes single-step fabrication of an equal submicron size porous photonic structure array through electrospraying. This distinctive approach involves a continuous supply of material with simultaneous removal of solvent for fabricating large area samples, compared to other processing techniques. The process optimization is carried out to regulate the pore diameter and spacing. Morphological studies showed the continuity of porous arrays extending to large areas of the order of millimeters. Optical investigations demonstrated that this uniform periodic topography assisted in improved light scattering and a consequent enhancement of light absorption. Further, the incorporation of this array structure in the active layer of organic photovoltaic devices is evaluated through both experiments and modeling. Modeling and simulations suggest that the optimized range of 200–500 nm pore size aids in higher current density. Experiments reveal an improvement of 18% in the photocurrent density at short circuit in the periodic array architecture compared to the planar reference. Therefore, in this study, a facile single-step novel method of obtaining photonic array structures with improved device performances is demonstrated.

Optical transport behavior of organic photo-voltaic devices with nano-pillar transparent electrodes is investigated in this paper in order to understand possible enhancement of their charge-collection efficiency. Modeling and simulations of optical transport due to this architecture show an interesting regime of length-scale dependent optical characteristics. An electromagnetic wave propagation model is employed with simulation objectives toward understanding the mechanism of optical scattering and waveguide effects due to the nano-pillars and effective transmission through the active layer. Partial filling of gaps between the nano-pillars due to the nano-fabrication process is taken into consideration. Observations made in this paper will facilitate appropriate design rules for nano-pillar electrodes.

A design to enhance the photocurrent density in an inverted bulk heterojunction organic solar cell is explored. Aluminum nanoparticles dispersed in the hole transport layer at the rear end of the device structure are observed to enhance the device performance through multiple effects including enhanced absorption and better charge collection. Modeling and simulations are used to understand the mechanisms of optical transport that underlie the enhancements which are experimentally observed.