Surface plasmon polariton mediated energy transfer from external antennas into organic photovoltaic cells

Abstract

Despite significant improvements in the performance of organic photovoltaic devices in recent years, the tradeoff between light absorption and charge separation efficiency remains pervasive; increasing light absorption by increasing the device thickness leads to a decrease in exciton diffusion efficiency and vice versa. In this thesis, I demonstrate organic solar cells with an external light absorbing antenna. Light is absorbed by the external antenna and subsequently transferred into the photovoltaic cell via surface plasmon polariton modes in an interfacial thin silver contact. By decoupling the optical and electrical functions of the cell, this new architecture has the potential to circumvent the tradeoff between light absorption and charge separation efficiency. Non-radiative energy transfer is discussed and modeling finds that efficient energy transfer is mediated by surface plasmon polaritons. Devices with two very different antenna systems are demonstrated experimentally. Antennas with high photoluminescence efficiency are found to exhibit energy transfer efficiencies of approximately 50% while strongly absorbing antennas exhibit increases in photocurrent as high as 700% when compared to devices with non-functioning antennas even with very low photoluminescence efficiencies near 4%. These results suggest that this new device architecture could lead to significantly higher power conversion efficiencies by allowing the independent optimization of the optical and electrical components of organic photovoltaic cells.