SBIR Phase I: Optimized multi-substituted fullerene n-phase for high performance organic photovoltaic (OPV) devices

This Small Business Innovation Research (SBIR) Phase I project targets the synthesis of fullerene derivatives with an isomer distribution sufficiently narrow to enable significant improvements in OPV performance. The intellectual merit consists in the development of methodology allowing for the scalable synthesis of specific isomers of multiple fullerene adducts such as C60(X)n with n= 2-3. Previous work has confirmed the predicted increase in open-circuit voltage for higher degrees of functionalization but current density dropped in some cases dramatically. This observation has been attributed to the increasingly wide distribution of electron-attracting properties of isomer mixtures resulting in electron sinks. Regio-selective synthesis of fullerene adducts is expected to lead to the absence of local electron traps and, therefore, to increased current density in bulk heterojunction solar cells without affecting other properties. Reversible addition reactions will be conducted to block reaction sites to limit the number of locations on the fullerene sphere available for subsequent functionalization with desired functional groups. Laboratory-scale bulk heterojunction OPV cells will be fabricated. Power conversion efficiencies of >8% are expected by increasing the current density in known systems and setting the stage for further improvements. The broader impact/commercial potential of this project will consist in the improvement of the performance of OPV devices to >8% enabling the deployment of large-scale OPV power generation without the need of government subsidies. Printing or roll-to-roll solution processing of highperformance solar cells will be possible, providing an ultra-low-cost alternative to conventional silicon or thin-film techniques. Solar cells at $0.50 to $1/watt-module with a life-cycle cost of energy of 7 to 8 cents/kWh will progressively become available. Up to now, 1.1 GW of solar PV has been installed in the US, of which 0.34 GW was installed in 2008. As one of the few photovoltaic systems that can reach gridparity without subsidies, or carbon credits, OPV has the potential to grow faster, and displace an increasing fraction of the approximately 2.9 trillion kWh/year of electricity produced in the U.S. from fossil fuels with no greenhouse gas and pollutant emissions. Dependence of foreign energy supply will be reduced thereby enhancing energy security and improving the country's trade balance. Availability of specific fullerene isomers or isomer groups with similar electronic properties will significantly impact the development of more fullerene applications such as other printable electronic devices, e.g., thin-film transistors.