Investigation of the Influence of Molecular Structure at Interfaces in Polymer Photovoltaic Devices.

Organic Electronic Devices;Photovoltaic;Electrode Interface;Donor Acceptor Interface;Open Circuit Voltage;Conjugated Polymer Alignment;Materials Science and Engineering;Engineering;Materials Science and Engineering

Bilby, David L.Shtein, Max ;

University of Michigan

关键词: Organic Electronic Devices;    Photovoltaic;    Electrode Interface;    Donor Acceptor Interface;    Open Circuit Voltage;    Conjugated Polymer Alignment;    Materials Science and Engineering;    Engineering;    Materials Science and Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/107045/bilbydav_2.pdf?sequence=2&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Organic photovoltaic devices embody the promise of inexpensive renewable energy. However, before these devices can become commercially successful a stronger understanding of the relationships between material structure, properties and device performance must be built. Interfaces within polymer photovoltaic devices are sites of processes critical to effective device function and are thus the focal point for ongoing research. We systematically investigated the effect of placing molecular spacers at the donor-acceptor interface. As we increased the thickness of the spacer layer we observed suppressed charge transfer, reduced dark current and reduced polaron binding which contributed to a decrease in current density and an increase in open circuit voltage. This result guides the design of materials which seek to mitigate the interfacial distance dependent trade-offs between charge transfer and recombination in order to improve device performance. We also investigated the influence of the molecular structure of the electrode-active layer interface. We found that insulating interfacial layers ensure diode rectification by breaking percolative-active material contact between non-selective electrodes. We also found that strong active layer-electrode interaction leads to charge blocking phase separation in the devices which deleteriously effects performance. This unwanted phase separation can be avoided by inserting a non-interacting interlayer. We also observed that acid- or base-like moieties can be used to modify the work function of ITO in order to achieve good electrical contact with the active layers of a device. These results provide molecular design guidelines for the fabrication of materials for the electrode interface of high performance devices. Besides the interface issues, the low charge carrier mobility of conjugated polymers (CPs) intrinsically limits the thickness, absorption, and performance of photovoltaic devices. We made aligned poly(3-hexylthiophene) films with an epitaxially directing additive and an off-center spincasting technique in order to take advantage of their anisotropic charge carrier mobility. These aligned films are applied in novel in-plane devices where the charge transport direction is abutted with the polymer alignment, providing large enhancements in the open circuit voltage. These results motivate the continued pursuit of CP alignment in devices in order to correlate molecular orientation with device performance.