Morphology control and material mixing by high-temperature organic vapor-phase deposition and its application to thin-film solar cells

Abstract

Organic vapor-phase deposition is used to growphotovoltaic cells consisting of molecular compounds that require high-evaporation temperatures. The organic crystal size and film morphology are controlled by adjusting the source evaporation temperature, substrate temperature, carrier gas flow rate, and chamber pressure. The resulting surface morphology produces a highly folded donor–acceptor interface with a fourfold increase in area compared with a planar heterojunction, leading to an increased exciton diffusion efficiency, and hence an 80% increase in photovoltaic cell power conversion efficiency. Mixed organic layers with controlled constituent ratios and layer thicknesses are grown by the simultaneous codeposition of multiple source materials.Photovoltaic cells comprised of a copper phthalocyanine: C 60 mixed layer show comparable performance to analogous vacuum-deposited cells.