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Printed Electronics

Organic light emitting diodes (OLED) and organic solar cells (OSC) based on polymeric materials are considered to exhibit a great potential in the product development of novel solar power, lower power consumption display und lighting technologies. They allow for an easy and cost-efficient production of large-area applications

 

To date, just a few niche applications have already been entered the market. However, the actual technology still suffers from lower efficiency due to basic physical limitations: common OLED materials are able to convert only 25 percent of all exited states into light emission. All generated triplet state electrons are deacitivated by non-radiative processoes. Therefore, three forth of all excited states are ultimately lost along with the generation of heat which, in hte long rund, adversely affects the organic material.

One solution to overcome this limitation ist the incorporation of appropriate metal complexes which, by the use of strong spin-orbit coupling, allow for the utilization of both singlet and triplet excited states to achieve nearly 100 percent internal quantum efficiency. Yer, this addition of organometallic triplett emitters will most probably result in undesired phase separation, aggregation and crystallization, which in turn can harm the device performance.

Therefore, the design of a suitable host system with covalently bonded phosphorescent chromophores has been regarded as the viable solution to address these issues.

On the other hand, OSC materials show only low efficiencies as a result of non-optimized morphologies and poor adjustment of the absorbing material to the solar spectrum. In particular the near red and infrared range of the light cannot be used effectively for the transformation of photons into free charge carrier. Since, moreover, the morphology of the polymer blend is crucial for the charge separation and conductance of charges to the electrodes and therefore for overall performance, an optimized alignment of the active layers is essential for further efficiency improvement.