In the area of organic solar cells, molecular materials has risen rapidly in recent years to performance levels on-par with or better than semiconducting polymers. Our group has been working on a molecular donor based on benzodithiophene, terthiophene and rhodamine (BTR) which showed remarkable performance in solar cells devices. The BTR material shows some interesting thermal properties (nematic liquid crystalline phase) which we are currently examining in greater detail.
Fullerenes and their derivatives are the most widely used electron acceptor materials in the organic solar cell area. Our group has expertise in the synthesis of fullerene (C60 and C70) derivatives, in particular, in the area of regioselective synthesis of bis-substituted fullerenes. We have also demonstrated the synthesis of fullerene derivatives in continuous flow. We have an on-going materials development program on non-fullerene acceptors.
The bulk material structure of block copolymers can be controlled by adjusting the relative size of the polymeric blocks. This is seen as an ideal approach to the control of active layer structure in bulk heterojunction solar cells. However, the synthesis of fully conjugated block copolymers is non-trivial with major problems in achieving well-define blocks through current synthetic methods. In this project, we are examining both sidechain modification and alternative synthetic strategies.
There are very few synthetic methods that allow the controlled synthesis (chain growth/living polymerisation) of conjugated polymers. We are looking into a combination of strategies to enable the synthesis of well-defined (molecular weight and end group control) conjugated polymers. One example is the construction of a two-dimensional bottle-brush polymer using Grignard metathesis polymerisation (GRIM) and ring opening metathesis polymerisation (ROMP) methods.
Flow synthesis of conjugated polymers
We have developed methods to synthesize conjugated polymers in continuous flow processing specifically to address the issue of scale-up for our large-area printed solar cell project. We have demonstrated a range of polymerisation reactions in flow including Suzuki-Miyaura coupling, Stille coupling, Grignard metathesis polymerisation and C-H activation direct arylation. In developing the methods, we found improvements in conventional polymerisations that led to improved molecular weights and ultimately solar cell device performance.
Supramolecular interactions and Self-Assembly
The emergence of organic electronics is transforming current electronic technologies that will lead to light-weight flexible devices such as foldable displays, building-integrated lighting and low-cost solar cells. The greatest improvements in efficiency and durability of devices will be achieved through precise control of material structure from molecular to bulk scales. We are addressing this problem by designing smart materials that can self-organise and enhance the properties required for specific applications. New insights gained in structure-property-function relations are being used to assemble well-defined macroscopic materials in organic electronic applications.
Nanowires and Networks
Our group has extensive experience in working with polycyclic aromatic hydrocarbons, in particular, hexa-peri-hexabenzocoronene (HBC). The large pi surface of the HBC molecules drives strong intermolecular association leading to the formation of nanowires and well-ordered bulk films.
Interface modification is now a commonly used method in organic electronics to improve the performance of a device. It serves a number of different functions that often have a synergistic effect. Firstly, interface modification can enhance the physical contact between two materials by smoothing a rough surface and reduce hydrophilic/hydrophobic repulsion. Secondly, ohmic contact between two materials can be achieved with the modification of surface work function. The third and most sophisticated effect is the interface directed organisation of molecules in the bulk material.