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Synthesis and Application of Block Copolymers for Interfacial Stability in Organic Solar Cells

Final Report Summary - SYNABCO (Synthesis and Application of Block Copolymers for Interfacial Stability in Organic Solar Cells)


Today, solar cells based on silicon are approximately 99 % of the global production of photovoltaic cells. However, present-day silicon technology has some disadvantages: purification processes are extremely expensive and silicon availability is limited due to its extensive use in the field of microelectronics. Consequently, the production cost of silicon solar panels is too high to be economically viable for every person worldwide. This is the major motivation for the development of organic photovoltaic devices (OPVs, also known as organic solar cells, OSCs), which exhibit advantages such as low cost, high device flexibility, and cheap fabrication from relatively abundant materials.1 OSCs can be produced into large roll-to-roll films (Figure 1).

Figure 1. Belectric OPV’s light weight and semi-transparent OSCs; and a laptop bag.

The inherent problems with OSC technology, however, are the stability (and therefore lifetime) and the relatively low efficiency (of converting the sun’s energy into electricity). SYNABCO’s objectives were to primarily address the former, to produce OSC devices with significantly longer lifetimes than the current 3 to 5 year estimates, through the design and fabrication of completely novel block copolymers. These block copolymers were designed to improve the stability of the devices through the use of low energy equilibrium structures which hold the photoactive materials in place. Concomitantly, the aim was to increase the power conversion efficiencies of the devices through more intimate contact of the individual components in the solar cells.

Two different libraries of block copolymers have been designed and synthesised to this end. Firstly, a family of poly(3-hexylthiophene)-block-poly(ethylene oxide) (P3HT-b-PEO) polymers was successfully fabricated by ‘Steglich esterification’ between P3HT-OH and PEO-COOH.2 The absence of metal contaminants in all of the copolymers has been further confirmed by SEM-EDXA. This is vital for the use of such material in an OSC device, where metal contaminants are well known to destroy device performance. Another, different, family of diblock copolymers, to be disclosed following appropriate IP protection, were simultaneously prepared, this time via click chemistry.

X-ray scattering experiments have been recently performed on all of the polymers synthesised and the data analysis is currently underway. The phase diagram of both libraries of materials will be constructed in due course.

The materials are currently under investigation at collaborating company, Belectric OPV, and the University of Pau, to identify the effect of SYNABCO’s new polymers on lifetime and efficiency in real OSC devices.

SYNABCO scientific results are predicted to contribute to both European excellence and competiveness by the development of more stable and more efficient OSCs and OSC-based devices. The results already obtained, and currently being generated, are expected to lead to a number of publications and one patent. SYNABCO IP will remain within the EU and thus any commercial products that arise from the results generated by SYNABCO will directly contribute to the competitiveness of the EU. The results of SYNABCO have been disseminated to researchers at Belectric OPV GmbH and members of a multinational Marie Curie ITN, ESTABLIS, working on the stability of OSCs. Now, these researchers are studying the role of our materials. Clearly, the more stable and more efficient OSCs that SYNABCO has produced benefits Belectric OPV directly by enabling them to capture an increased share of the OSC market.

References:

1. C. J. Brabec and J. R. Durrant, MRS Bull. 2008, 33, 670.
2. H. Erothu et al., Polymer Chemistry, 2013, 4, 3652.