Nanostructured Extremely Thin Absorber Solar Cells

Abstract

The introduction of nanostructured metal oxides as electron acceptor resulted, among others, in the concept of extremely thin absorber cells. Thus, inorganic semiconductors like Sb2S3 can be utilized as sensitizer, which typically possess promising properties, such as a tunable band gap and a high extinction coefficient. Furthermore, low quality/crystallinity requirements of the layer due to a small thickness allow the application of low cost fabrication methods, such as chemical bath deposition. However, a detailed characterization of intrinsic properties is unavoidable in order to find the best device architecture and suitable material combinations for highly efficient solar cells.This study focuses on the fabrication, optimization, and characterization of Sb2S3 coatings and Sb2S3 based solar cells. For this purpose, chemical bath deposition conditions and parameters, i.e., deposition temperature, positioning of the substrates, immersion time, and pre- and post-treatments have been examined and resulted in a detailed recipe for the fabrication of high quality Sb2S3 coatings. In combination with optimized layer thicknesses and crystallization conditions of Sb2S3 and P3HT, efficiencies of over 3.2% could be achieved with flat heterojunction solar cells.In order to identify intrinsic limitations, which prohibit further improvement of efficiency, more detailed and comparative measurements with P3HT:PCBM cells have been done. Thus, revealing monomolecular recombination processes of excitons, a potential dependency of charge separation, and long charge carrier pathways as main loss mechanisms of fabricated flat heterojunction cells. Furthermore, investigation of several hole transport materials revealed a disadvantageous influence on charge generation due to the parasitic absorption of light by the hole transport material.Based on the results obtained from Sb2S3 based flat heterojunction solar cells, the use of nanostructured metal oxides in combination with transparent hole transport materials is proposed to possibly overcome some of the found limitations.