Diffraction gratings and buried nano-electrodes - architectures for organic solar cells

One limiting factor to the efficiency of the bulk heterojunction solar cell is the weak absorbance of the thin photoactive layer. The thickness is restricted by the small charge carrier mobility. Two cell concepts-light trapping with diffraction gratings and buried nano-electrodes-were investigated. Optical simulations based on rigorous coupled wave analysis were performed with supporting experiments in order to evaluate the concept of an embossed diffraction grating in the active polymer film. An increased absorptance in the active layer is calculated for transversal electric polarisation. High losses in the corrugated aluminium electrode in transversal magnetic polarisation would require a displacement of the corrugated boundary between two dielectrics. The second approach is based on vertical nano-electrodes. The planar semi-transparent electrode is substituted by comb-like array of electrodes embedded in the photoactive polymer blend. The potential of this approach is discussed and initial experimental results are presented.