The effect of selective contact electrodes on the interfacial charge recombination kinetics and device efficiency of organic polymer solar cells

Organic polymer solar cells (OPSCs) have been prepared using TiO(x) metal oxides as selective electrodes for electron collection. The interfacial charge transfer reactions, under working conditions, that limit the energy conversion efficiency of these devices have been measured and compared to the standard OPSC geometry which collects the electrons through a low work function metal contact.     

A finite element approach to the position problems in open-loop variable geometry trusses

The present paper looks at some kinematic and static-equilibrium problems that arise with variable-geometry trusses (VGTs). The first part of the paper looks at the use of active controls in the correction of static deformations, the second part at the position problems. The separation between deformable- and rigid-body displacements makes it possible to consider separately the corrections in each component of the structure. VGTs are considered as open-loop linkages with redundant rigid-body degrees of freedom. Owing to this redundancy, possible solutions to the inverse problem are in general infinite, for which reason it is necessary to use some optimization criteria. To tackle the problem an optimization procedure with constraints is developed for the purpose of minimizing the displacements of the actuators. Suitable use of the constraints allows us to solve the direct position problem using the same optimization procedure.     

A procedure based on finite elements for the solution of nonlinear problems in the kinematic analysis of mechanisms

In the present paper the kinematic analysis of mechanisms is based on the application of finite elements is discussed. It is shown how the kinematic properties of the rigid-body motions of a mechanism can be obtained from an analysis of the stiffness matrix of a simple model comprising rod-type elements in the case of planar mechanisms. In the event that there is also a more complex finite element model of the mechanism, onemay in addition obtain thenode values from the results achieved with the simple model. Special attention is given to nonlinear position problems, i.e. initial, successive, deformed, and static equilibrium. An error function is provided that is valid in each case. This function is derived from the elastic potential function, and uses Laggrange multipliers and penalty functions. The result is an application of the primal-dual method, or augmented Lagraange multipliers (ALM) method. This function is minimized by means of Newtons' method, which leads in simple form to the vector gradient as a force vector. The second-derivative matrix is derived from the stifness matrix, to which a complementary matrix owing toe nonlinearity introduced by the large displacements is added.

This method can be easily implemented on a computer. The computer program will be able to perform a wide variety of kinematic analyses of any planar mechanism with lower pairs. The models of the mechanism are very simple, and need only a few tens of degrees of freedom even for the most complex mechanisms. The CPU time is also very low due to the simplicity of the method and its good convergence properties.     

Novel ZnO nanostructured electrodes for higher power conversion efficiencies in polymeric solar cells

1-Dimensional nanostructured ZnO electrodes have been demonstrated to be potentially interesting for their application in solar cells. Herein, we present a novel procedure to control the ZnO nanowire optoelectronic properties by means of surface modification. The nanowire surface is functionalized with ZnO nanoparticles in order to provide an improved contact to the photoactive P3HT:PCBM film that enhances the overall power conversion efficiency of the resulting solar cell. Charge extraction and transient photovoltage measurements have been used to successfully demonstrate that the surface modified nanostructured electrode contributes in enhancing the exciton dissociating ratio and in enlarging the charge lifetime as a consequence of a reduced charge recombination. Under AM1.5G illumination, all these factors contribute to a considerably large increase in photocurrent yielding unusually high conversion efficiencies over 4% and external quantum efficiencies of 87% at 550 nm for commercially available P3HT:PCBM based solar cells. The same approach might be equally used for polymeric materials under development to overcome the record reported efficiencies.