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Abstract

Organometal halide perovskites are a class of semiconducting compounds which marked the research in the photovoltaic field by their excellent optical and electronic properties convenient for light harvesting applications. In a 7 year period of research and their application in solar cells, power conversion efficiencies surged to over 21%, which was only a decade ago unimaginable for mainly solution processed solar cells. Albeit the high power conversion efficiency, there are several issues that need to be addressed before the technology becomes mature for industrial scale production. Solution processing of organolead halide perovskites is typically performed by using toxic, high boiling point solvents. In addition, the occurrence of other structural phases as nonstoichiometric residues during the film formation is directly connected to the atmospheric conditions during crystallization. In order to overcome these problems I introduce a straightforward, scalable and environmentally friendly synthesis of submicron sized stoichiometric perovskite particles, which can be afterwards deposited in the form of an ink on large area substrates. Synthesized particles are applied in a photoconductor in which the dominant photoconducting charge type is revealed.
Currently the most efficient perovskite solar cell structures implement metal oxide electron transporting layers which require complex processing with high temperature sintering, are unstable under ultraviolet (UV) light irradiation and cause interface charge build up which results in electrical instabilities in the form of hysteresis. Here I present a novel approach of using self assembled siloxane functionalized fullerenes on an optically transparent conductive oxide electrode as an effective electron extracting layer in perovskite solar cells. It is demonstrated that a 1.5 nm thick monolayer, formed by a low temperature dip coating method, is enough to obtain a UV stable charge selective interface.
Transition metal dichalcogenides, particularly MoS₂ and WS₂ belong to a large family of layered, quasi 2D materials which have a common feature anisotropic layered like growth with characteristic weak interlayer interactions. This property allows one to isolate individual sheets from the parent crystal by means of exfoliation techniques. As band gap tunable semiconductors with rich surface chemistry they have proven to be promising materials for numerous thin film optoelectronic devices. As a proof of concept, I present exfoliated WS₂ applied as an inorganic hole transporting layer in perovskite solar cells, which resulted in a 6% of stabilized solar cell power output. Furthermore I propose perovskite WS₂ band alignment supported by an indirect indication of charge transfer over the perovskite WS₂ interface.
Lastly, specific surface functionalization applied on chemically exfoliated MoS₂ is presented by decorating MoS₂ nanosheets with gold nanoparticles directly in a colloidal suspension. This led to their homogeneous incorporation into an elastomer by virtue of strong gold thiol interaction. Together with the possibility of induced metal to semiconducting phase transformation in MoS₂ we produced a matrix of metallic and semiconducting parts by a laser induced phase transition.