UMWELTnanoTECH

UMWELTVERTRäGLICHE ANWENDUNGEN DER NANOTECHNOLOGIE

8 Environmentally friendly, high-efficiency organic solar cells (EOS)

Field of work:

The goal of this project is the development of a physical/technical basis for the environmentally friendly and sustainable production of high-efficiency organic solar cells (OSC). In the area of organic photovoltaics (OPV), solar cells based on polymers and fullerenes (polymer blend solar cells) have become established. They rely on wet chemical processes and have since made the jump to high efficiency levels. OSC currently reach certified efficiency levels of over 10 %. It is now the right time to consider aspects of this attractive PV technology which were little thought about in the past . As part of the research work, high-efficiency OPV functional layers and solar cells with environmentally friendly compositions ("green" solvents) are being developed and characterised in a comprehensive manner. The main goal of this project is the development of high-efficiency solar cells which are suitable for an environmentally friendly and highly productive mass print process. Here the morphology of the absorber mixed layer plays a major role. Due to different solubility of the organic semiconductors, different domains are created with a size which depends on many factors and typically lies in the nanometer area (smaller than 50 nm). Electrical conductivity, optical absorption, efficient charge carrier generation as well as minimal recombination losses determine the suitability of the nanomorphology.

In the first year we were able to classify additives regarding their boiling point, their volatility, and their solubility. The greatest improvements result from the use of high-boiling additives with a selective solubility for PCBM as an electron acceptor. Their use leads to a rougher microstructure and an increase in the phase separation. With the combination of different environmentally friendly solvents, comparable levels of efficiency could be achieved with respect to "non-environmentally-friendly“ halogenated solvents.