EAPSI:Investigating the Ultrafast Charge Dynamics in Polymer Solar Cells Incorporating Nanostructured Silver Electrodes

Petoukhoff Christopher E, Piscataway NJ

Investigators

Abstract

In the search for sustainable energy sources, low energy consumption technologies are critical to minimize our environmental impact and maximize the energy harvested. Polymer solar cells are lightweight, flexible alternatives to traditional solar cells and have potential energy payback times as low as one day (compared to >2.5 years required for solar cells made from silicon), if their efficiency can reach >15%. One way to improve the efficiency of polymer solar cells is to employ light-trapping techniques, such as using nanostructured metallic electrodes. While polymer solar cells incorporating metallic nanostructures are known to have improved light absorption in the polymer active layer, this does not always translate to improved electrical output. This study seeks to fundamentally understand why improved light absorption does not necessarily lead to improved electrical output in the presence of nanostructured metallic electrodes. To do this, ultrafast time-resolved photoinduced absorption measurements will be conducted at Okinawa Institute of Science and Technology in collaboration with Professor Keshav Dani, who is an expert in conducting ultrafast time-resolved measurements. Nanostructured Ag electrodes will be fabricated with the structure of Ag nanoparticle arrays on a Ag thin film (AgNPA/Ag). To mitigate the effects of charge recombination at the AgNPA surface, a series of ultrathin interfacial layers (exfoliated MoS2, Ag2O, and graphene oxide) will be applied to the AgNPA/Ag and compared to AgNPA/Ag without an interfacial layer. The prototypical polymer:fullerene blend, P3HT:PCBM, in which the photophysics are well-established, will be used as the active layer coating. Two-color pump-probe measurements will be employed, in which P3HT:PCBM will be optically pumped with a wavelength within its absorption band, and the probe wavelengths selected will be those corresponding to photoinduced absorption from P3HT excitons (bound electron-hole pairs) and P3HT:PCBM polarons (free electrons and holes) over a time scale of tens of fs to 1 ns. This will allow the elucidation of whether the initially improved population of excitons in the P3HT:PCBM layer translates to an improved polaron population, with the expectation that both exciton and polaron photoinduced absorption should both be greater in the presence of the passivated AgNPA/Ag, which would eventually translate to improved solar cell device efficiency. This NSF EAPSI award is funded in collaboration with the Japan Society for the Promotion of Science.