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Abstract

During the last years, several frameworks for developing PSSs arose, which vary in focus. Examples of their focuses are engineering processes, technology, knowledge engineering, services or tangible products. However, just a few frameworks concentrate on the market or, specifically, the customer. As the customer is the key success factor of any product, we have developed a framework for designing PSSs by adapting an existing technology-centered framework. Our framework describes the perspective of increasing customer acceptance using PSS. Increasing customer acceptance means to reduce the effects and influences of customer barriers, e.g. unnecessary high costs of purchase or a lack of trust in the product's reliability. The model consists of three layers and the strategy space. The layers are the customer layer, the barriers layer and the solution layer. The customer layer describes the customers and the target groups of customers, who the PSS aims at. The barriers layer includes all customer barriers that are to be reduced by the PSS. The solution layer describes the PSS and its components; tangible elements, intangible elements and the infrastructure for connecting all elements. This layer shows how the PSS is realized to reduce the customer barriers of the focused target group. As other goals and influences affect the design of a PSS, the strategy includes external factors. Those external factors are generated by the company itself (e.g. other departments, product portfolio) or by external stakeholders or sources (e.g. suppliers, laws). Our model helps designers to understand the proceeding to design a PSS for increasing customer acceptance by reducing customer barriers.

We developed a finite element model of a finger structure polymer solar cell in conventional architecture in order to investigate current pathways and dissipative power losses. The model is of purely resistive nature, as this is sufficient to describe the effects under consideration. The model simulations yield the spatial distribution of the current densities, potentials and the according dissipative losses. In particular, the current pathways are spread out from the entire length of the top contact towards the entire width of the ground contact, running along the electric potential gradient. On the other hand, current crowding appears at the foremost part of the top electrode, resulting in a respective concentration of the resistive loss in this vicinity. The overall behavior of the current, mostly steers the resistive behavior of the device and is a delicate consequence of the interplay between the individual layer properties, namely the resistivities and layer thicknesses in combination. All this provides a first step towards a detailed quantitative description of the losses, depending on the geometrical cell design. The dissipative loss, in turn, is the origin of heat, which is observable by lock‐in thermography experiments, which are aimed to be reproduced by simulation.

of organic solar cells with PCDTBT donor polymer: An interlaboratory study.

Appreciable progress has been achieved in the development of organic photovoltaics (OPV) over the last decade. However, further improvement of operational stability remains a challenge. In this contribution, focus is placed on corrosion and delamination of the metal contact, which are mainly caused by oxygen or water vapor ingress but in other cases also via mechanical wear and different thermal expansion coefficients. So-called pinholes and electrode edges provide pathways for ingress of water vapor and oxygen, which may attack the metalorganic interface. Thus, electrical insolation via formation of insulating metal oxide and concomitant mechanical delamination occurs. As charge injection and extraction is suppressed at insulated and delaminated areas, the active area contributing to power conversion gets reduced. This work links analytical and numerical predictions about the active area in contact with the electrode to experimentally observe dependencies. Spatially and time-resolved electroluminescence measurements provide information on location, size, and growth-rate of insulated areas. Area loss rates for dark spots depend either sub-linear (for early stages and edge-ingress) or linear (later stages) on time. The initial defect size has a clear impact on growth rates. Furthermore, it has possible to demonstrate titanium oxide interlayers to slow down this type of extrinsic degradation.

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Organic solar cells are promising candidates for future photovoltaic applications with benefits due to their low production costs, flexibility, conformity, color and wide-range applicability. Presently, efficiencies of approx. 12% [1] make organic solar cells suitable for commercial applications. The necessary size-upscale, alas, cause severe problems in terms of dissipative losses of several kinds from inside as well as outside the photoactive polymer layer. In order to solve these problems, all possibilities of improvement concerning choice of materials/material combinations, processing and geometrical design have to be considered [2]. The key to this is a deep inside understanding of the underlying physical mechanism and their interplay. Here, the essential first step is to quantitatively represent the losses on the geometrical design. This is where thermographic imaging as a fast and effective tool for the measurement of dissipative losses comes into play. Thermographic imaging, as in dark or illuminated lock-in themography (DLIT/ILIT) is excellently suitable to represent the aforementioned losses under operating conditions [3][4][5]. Empowered by the lock-in technology, dissipative losses appear instantaneously in their geometrical distribution. Figure 1 presents the DLIT image of an organic solar cell excited under forward bias (taken from [6]). In addition to the strong heat pattern in the 2.5mm wide active layer area, there is a weak pattern in the further course of the device in the vicinity of the contacting electrode (right hand side of the active layer. On the basis of the figure, losses with strong localisation are visible as well as weaker patterns in the vicinity. By complementary measurements and modelling calculations the losses can be traced back to the current profile of the organic solar cell. An example of this is the microdiode model (see, e.g. [7]) suitable to calculate various physical properties to the loss and current patterns of the devices. In particular, the effect of "current crowding" at the edges of the active layer is assumed to lead to loss patterns of the kind presented in figure 1. Further understanding of the physical properties is necessary to improve the performance in order to meet the requirements for upscaling of organic solar cells to technological relevant modules. Thermographic imaging has already demonstrated to be a valuable tool for the measurement of a wide range of their physical properties and will certainly prove itself to be of even larger importance once various material combinations, processing methods and design variations are to be investigated.http://dx