**8. Acknowledgment**

112 Solar Cells – New Aspects and Solutions

This mold is then used for creating NRs in a film of a conjugated polymer (e.g. regioregular P3HT). The created polymeric rods (Fig. 13c) show an increased crystallinity and preferential alignment of the polymer molecules in the vertical direction (Aryal et al., 2009) as well. The spacing between the polymer rods can then be filled with an acceptor material.

Kim et al. used NIL to create a nanostructured solar cell combining the molded polydithiophene derivative TDPDT with PCBM leading to a PCE of 0.8% compared to 0.25%

Fig. 13. (a) Silicon mold created by ICP etching using a AAO template as mask (inset image: side view of the mold); (b) illustration of the molding process applied to P3HT; (c) molded parallel aligned P3HT nanopillars. Reprinted with permission from (Aryal et al., 2009).

Hybrid solar cells are still lagging behind the PCBM based OPV technology in respect of device performance and maturity for commercialization. They are currently under development and evaluation in basic research and have the potential for further significant improvement. The additional absorption of photons by semiconductor NCs, their potential to utilize multiple excitons generation and their higher electron conductivity compared to organic acceptor materials are some of the reasons behind. Novel device structures, the implementation of nanostructuring methods and the development of lower band gap material able to convert the NIR and IR parts of the solar spectrum into electrical energy will probably lead soon to PCE values of 10% and beyond for OPV technologies (Dennler et al., 2009). It is expected that the hybrid solar cell technologies also benefit from this development since device structure, nanostructuring methods and the development of novel low band gap polymers are overlapping aspects with pure OPV approaches. Progress in the development of organic-inorganic hybrid material design will not only be beneficial for the development of hybrid solar cells but also for various applications such as light emitting diodes, photodetectors etc. and have therefore a broader application potential beyond photovoltaics. In addition the energy levels in inorganic-organic hybrid materials can be tuned more easily compared to pure organic composites based on to the size quantization effects occurring in semiconductor nanostructures which might be beneficial for dedicated applications and allows a broad design flexibility for the variation of material composites. Nevertheless one can clearly deduce from Table 1 that in all 1st and 2nd generation of PV technologies, differences between module PCEs and values of the best research cells are

After the evaporation of a top electrode the hybrid solar cell would be complete.

of a bilayer structure (Kim et al., 2007).

(b) (a) (c)

Copyright 2009 American Chemical Society.

**7. Outlook** 

Financial support from the German Federal Ministry of Education and Research (BMBF) within the project "NanoPolySol" under the contract No. 03X3517E as well as from the German Research Foundation (DFG) graduate school GRK 1322 "Micro Energy Harvesting" is gratefully acknowledged.
