Fundamental investigations on periodic nano- and microstructured organic solar cells

Using organic semiconducting materials in solar cells is a new approach with <br>promising possibilities. The great potential of low cost production combined <br>with mechanical flexibility gives rise to new applications. Due to the relatively simple fabrication process from solution and the mechanical flexibility, the production of organic solar cells by the cost effective roll-to-roll process appears promising. However, the preconditions for commercialization are not fulfilled as yet. The demands on organic solar cells strongly depend on the type of application. The highest demands on solar cell technologies are set by the energy market. Organic solar cells are only expected to be competitive on the energy market when the requirements on efficiency, lifetime and costs are fulfilled at the same time. Regarding this as a long term goal, a less demanding but still challenging medium term goal would be the application of relatively small organic solar cell modules for i.e. portable electronic devices. The integration of Organic Field Effect Transistors (OFET) and Organic Light Emitting Diodes (OLED) to all-polymer electronic devices is still under development. Nevertheless, the integration of organic solar cells as one functional component appears promising as the production technologies are expected to be compatible. <br> <br>The innovative contribution of this thesis to the development of organic solar <br>cells is as follows: Motivated by the desire to fabricate efficient and cost effective organic solar cells, the approach of developing novel solar cell architecturesbased on periodic nano- and microstructures is followed. At present, planar organic solar cells with indium tin oxide (ITO) as a transparent electrode are intensively studied. One decisive cost factor would, however, be the indium price, which is the key component of the ITO electrode. The planar cell architecture can be conceived as a one-dimensional photonic device, however <br>the presented work widens the investigations by a further dimension. Three <br>different device architectures based on - diffraction gratings, microprisms and <br>buried nanoelectrodes - are investigated in this thesis. <br> <br>Light trapping with diffraction gratings is reported as a promising approach <br>to increase the light absorption in the photoactive layers by coupling the light <br>into the thin photoactive absorber of the solar cell. This approach is investigated in this thesis by optical modelling and experiments. Optical modelling is performed by rigorous coupled wave analysis (RCWA) in order to calculate an optimum grating geometry and to gain a better understanding of the light absorption in the device. Diffraction gratings are introduced by micropatterning of the photoactive layers which are then characterised by scanning electron microscopy (SEM), absorption- and spectral-response measurements. Two novel cell architectures, based on microprisms and buried nanoelectrodes, are developed. <br>The microprism solar cell architecture can be regarded as a folded planar cell <br>and should benefit from an increased light absorption due to a twofold reflection of the incident light. ITO is substituted by a polymer anode which <br>is supported by a metal grid. Optimum dimensions of the system are derived <br>from optical and electrical simulations. Experiments are presented which cover <br>specific aspects like the thin film formation and the deposition of the microgrid to the characterisation of complete microprism solar cells by current-voltage <br> <br>Buried Nanoelectrodes form a comb-like array of vertically orientated electrodes <br>embedded in the photoactive layer of the solar cell. An improved charge <br>collection and light absorption shall be achieved. In addition, the cost intensive ITO is substituted by either one of the two options: asymmetric or interdigital buried nanoelectrodes. These are both investigated. Asymmetric buried nanoelectrodes are obtained by substituting one electrode of the planar device by a lamellar interconnected electrode. The substitution of both planar electrodes by buried nanoelectrodes results in an interdigital electrode set-up. <br>The planar organic solar cell built up on an ITO-coated glass substrate serves <br>as a reference system for the new cell architectures. Fundamental aspects like <br>optical modelling and morphology and specific aspects like the investigation <br>of different electrodes and the inversion of the layer sequence are investigated.

Author dc:creator

• Niggemann, Michael

Contributors dc:contributor

• Menz, Wolfgang

• Organische Solarzelle
• Lichteinfang
• Nanoelektrode
• organic solar cell
• light trapping
• microstructure
• nanoelectrode
• optical modelling

Repository record source_url

https://freidok.uni-freiburg.de/data/2092

OAI identifier oai:identifier

oai:freidok.uni-freiburg.de:2092