ISOPHOS 2015 - International School on Hybrid and Organic Photovoltaics

Multiscale simulation approaches combining models on different scales from the atomistic to the continuous are gaining increasing importance for the simulation of electronic devices. In this lecture approaches for such coupled simulations are presented, which are suitable for electronic transport and optical properties in inorganic and organic semiconductor devices. The necessity for multiscale simulations will be discussed, and different coupling schemes like the bridge and overlap methods are introduced. The particular interest in multiscale approaches for modeling of solar cells will be addressed. Since in most cases device simulations are multiphysics problems, we illustrate how the relevant models describing strain (linear elasticity, valence force fields), electronic states (k-dot-p, tight-binding), electronic transport (drift-diffusion, Monte-Carlo, non-equilibrium Green’s functions) and optical properties (Lambert-Beer, Maxwell solution-based) can be integrated in a multiscale/multiphysics simulation environment. The interaction between atomic and continuous media models is described, focusing on a top-down approach where the generation of the atomic structure is based on the macroscopic device description, including the association between atomic structure and finite element mesh and interpolation of physcial quantities. Examples of coupled simulations of III-nitride based quantum well and quantum dot structures, nanocolumns and transistors will demonstrate the main features and critical points of multiscale device simulations.

Starting from a brief overview of the current photovoltaics market and requirements for upcoming solar cell technologies, the lecture will focus on why reliable measure

Organic photovoltaic (OPV) technologies continue receiving skeptical approach from the industry and decision makers, despite the rapid progress in the device efficiency demonstrated in recent years. One of the primary reasons is the concern over the lifetime and the upscaling of the OPV products. Despite the promising literature reports it remains unclear what is the lifetime of the OPVs today, if the OPVs can become a reliable technology and if they can be manufactured in mass production. The talk will give a general overview of what is the status of the OPV stability today and what is expected in the near future. A list of failure mechanisms will be discussed, as well as various methods will be addressed that help improving the stability of the OPV technologies. This will follow with the discussion of the challenges related to upscaling of OPVs and what has been accomplished so far.

Organic photovoltaics (OPVs) are among the most promising photovoltaic technologies for long term sustainable energy production. Incorporation of plasmonic nanoparticles for absorption enhancement offers an attractive way to realized OPVs with efficiencies higher than 10%. On the other hand, the utilization of solution processable graphene in OPVs can offer many advantages such as the possibility of producing and processing them in large quantities, in a cost effective manner. Furthermore, graphene and graphene-like 2d materials can replace traditional electrodes, or buffer layers, but more importantly enable whole new device concepts, at longer term. In this lecture, I will report the current status on solution processable graphene (SPG) materials development and plasmonic device engineering to significantly enhance the performance and stability of OPVs. In particular, I will address recent advances in the rapidly developing field of plasmonic OPVs, in which various metal nanostructures (NPs) are introduced into the device. The effects induced by the NPs incorporation will be examined from the optical and electrical aspects. In the second part of my talk, I will give an overview of the progress of the recent research on graphene and its derivatives utilization as various components in OPVs, including transparent electrodes, buffer and active layers. Particular attention will be paid to the functionalization, doping and processing of graphene derivatives targeting in tunable optoelectronic properties with respect to the specific targeted application.

The lecture will describe the Kinetic Monte Carlo approach for calculating solar cell characteristics and show how it is linked to molecular dynamics studies that in turn are related to electronic structure calculations.

The lecture will give an overview of the construction principles of photovoltaic devices with special focus on organic solar cells. Coming from a functionality perspective (charge carrier separation, recombination, light incoupling, current collection), concrete materials and device stacks of state of the art organic solar cells as well as different module architectures will be presented, showing their possible advantages and remaining challenges. The interrelation between the final module architecture and device stack will be discussed as well.

Building Integrated PV systems (BIPV) in modern buildings with a large glazing area is a topic generating much interest; since they can significantly contribute to the amount of electrical energy produced from renewable resources taking into account also the building aesthetics and providing additional functions to the building envelope. However, at the same time it is necessary to overcome indoor overheating and glare issues in such a building. Switchable windows provide a solution to this problem as they can be switched between the dark to the bleached state without disturbing the visual contact with outdoor surrounding. A smart solution offers a product combining photovoltaic (e.g. DSSC components) and electrochromic (EC) device which could improve the power balance of buildings beyond the extent of using PV or EC device alone. The state of the art and the current progress of the combined PV-EC components/materials integrated in a single device will be presented taking into account also the recent developments within the ongoing WINSMART (FP 7 project).The combined PV-EC devices will be discussed also within the context of the MultiscaleSolar COST Action. These devices are a suitable topic for the multiscale research developed by this collaborative network which studies these issues from the atomistic to device scales in order to further evaluate their industrial perspective.