Layer-by-layer Deposition of Silicon Phthalocyanines-based Organic Photovoltaics

Abstract

With the need for the development of renewable sources of energy, organic photovoltaic (OPV) has been attracting researchers’ interest for the past decades. This solar technology utilizes carbon-based semiconductors instead of conventional inorganic materials which enables inexpensive, lightweight and flexible roll-to-roll fabrication of large area solar panels with a very short energy payback time. Device efficiencies have rapidly increased to above 18% within the last few years, becoming competitive with solar technologies available on the market. However, research has been focused on the maximization of efficiencies at all cost leading to synthetically challenging materials and processes with negligible commercial scalability. In this thesis, silicon phthalocyanines (SiPcs), synthetically facile molecules most known for their extensive use as dyes and pigments in the industry, were employed as low-cost and scalable active materials for OPV devices. We also report the use of layer-by-layer deposition of the donor and acceptor layer providing a more scalable process compared to the conventional blended heterojunction morphology. Different SiPc derivatives, both soluble and non-soluble, were used as acceptors, paired with different donor polymers (P3HT, PCDTBT, and PBDB-T) and integrated into hybrid evaporation-solution and all-solution layer-by-layer OPV devices. Significant device engineering and optimization was performed through the investigation of several processing conditions such as solvent choice, spin-speed, concentration and annealing temperature/time. In particular, all-solution processed SiPc-based bilayer OPV devices achieved PCEs above 3% with Voc above 1 V, which was similar to performances of corresponding BHJ OPVs. SiPc derivatives also demonstrated their ability to act as electron transport layers in perovskite solar cells. These results further establish the potential of SiPc derivatives as active materials in different solar technologies, while promoting the use of the bilayer structure in OPV devices.