New Molecular Materials for Energy-Based Optoelectronics: Solar Energy and Lighting

We have taken a materials intensive approach to developing an understanding of the mechanism of photocurrent and photovoltage generation in organic photovoltaic devices (OPVs).   We have investigated a wide range of new and established materials to investigate the connection between the OPV open circuit voltage (Voc) and the energy difference between the donor HOMO and acceptor LUMO energies (ΔE_DA).  Within closely related families of materials there is a clear correlation between Voc and ΔE_DA, however, we have found marked differences between the Voc values for materials systems with very similar ΔE_DA values.  I will present a model that we have developed that accurately couples Voc and ΔE_DA values with a D/A coupling term.  This approach gives us a new path to develop high Voc materials
     We have explored the use of metal porphyrin complexes as donor materials in OPVs.  The complexes we have chosen have high nonplanar structures in the ground state and excited state.  I will discuss the use of both simple and pi-extended porphyrins, illustrating how these materials can be used to enhance both the efficiency and Voc.  
     The exciton is a critical part of each of these processes, and being able to control the location, lifetime and energy of the exciton is essential to achieving high efficiency.   We have investigated methods for tuning exciton energies and controlling their migration paths, both intramolecularly and within a thin film.  I will discuss our most recent work with porphyrinic materials for OPVs.  This involves a careful materials design study that leads to both low energy absorption (into the nearIR) and the use of substituted porphyrins to efficiently harvest photons through the entire visible spectrum.   Both long wavelength and broad absorption are achieved with high extinction (> 10^5 cm 1).