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

在寻找可持续能源的过程中，低能耗技术对于最大限度地减少对环境的影响和最大限度地利用能源至关重要。聚合物太阳能电池是传统太阳能电池的轻量、灵活的替代品，如果效率能达到15%，其潜在的能源回收期低至一天（相比之下，硅太阳能电池需要2.5年）。提高聚合物太阳能电池效率的一种方法是采用光捕获技术，例如使用纳米结构的金属电极。虽然已知含有金属纳米结构的聚合物太阳能电池改善了聚合物活性层的光吸收，但这并不总是转化为改善的电输出。这项研究试图从根本上理解为什么在纳米结构金属电极存在的情况下，光吸收的改善不一定会导致电输出的改善。为此，将在冲绳科学技术研究所与Keshav Dani教授合作进行超快时间分辨光诱导吸收测量，Keshav Dani教授是进行超快时间分辨测量的专家。在银薄膜（AgNPA/Ag）上制备银纳米粒子阵列结构的银纳米电极。为了减轻AgNPA表面电荷复合的影响，将在AgNPA/Ag上施加一系列超薄界面层（剥落的MoS2、Ag2O和氧化石墨烯），并与没有界面层的AgNPA/Ag进行比较。将以光物理性质成熟的典型聚合物：富勒烯共混物P3HT:PCBM作为活性层涂层。将采用双色泵浦-探针测量，其中P3HT:PCBM将以其吸收带内的波长进行光泵浦，所选择的探针波长将对应于P3HT激子（束缚电子-空穴对）和P3HT:PCBM极化子（自由电子和空穴）在数十fs至1ns的时间尺度上的光诱导吸收。这将有助于阐明P3HT:PCBM层中最初改善的激子数量是否转化为改善的极化子数量，并期望在钝化AgNPA/Ag存在下，激子和极化子的光诱导吸收都应该更大，这最终将转化为提高的太阳能电池器件效率。NSF EAPSI奖是与日本科学促进会合作资助的。

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.