The Effect Of Silver Nanoparticles On The Performance Of Organic Solar Cells

With increasing consumption of fossil fuels and the urgent need to develop new energy sources, solar energy is sought after by all countries in the world as renewable and environmentally friendly energy. Photovoltaic solar cells making use of the photovoltaic effect are a significant aspect for utilizing solar energy. Compared with inorganic solar cells, organic solar cell (OSCs) has attracted a lot of attention owing to its light weight, ease of manufacture, abundant material resources and compatibility with flexible substrates. Currently, low power conversion efficiency (PCE), which could not reach the requirements of industrialization, is the major bottleneck of the development of OSCs. Therefore, improving the energy conversion efficiency of OSCs has become the research focus of scientists around the world. Surface plasmon resonance effects of metal nanoparticles(NPs), which can improve the light absorption of organic solar cells, has become an effective technique to improve the PCE of solar cell. But the bare metal NPs directly contacting with active layer can promote charge recombination and exciton quenching losses. In this paper, we introduce the silica-coated silver nanoparticles into OSCs or insert an isolation layer for separating silver nanoparticles with active layer to solve the current problems in this technique and more effectively improve the overall performance of devices. The silver nanoparticles (AgNPs) and silica-coated silver nanoparticles (Ag@SiO2) have been prepared and characterized, and then are introduced into the organic solar cells based on P3HT:PCBM active material. On this basis we study the influence of localized surface plasmon resonance effects of silver nanoparticles and silica-coating or a spacer for separating silver nanoparticles with active layer on the PCE of P3HT:PCBM-based solar cells. The specific work is as follows:1. We synthesize the silver nanoparticles of which the morphology and size can be controlled by liquid chemical methods, and then the AgNPs with average particle size of30nm is coated with silica of6-8nm thickness by TEOS hydrolysis.2. The P3HT:PCBM based bulk heterojunction solar cell is optimized by varying the mixed ratio of P3HT to PCBM, the concentration of P3HT:PCBM, the thickness of P3HT:PCBM film and thermal annealing process. Results suggest that the optimal P3HT:PCBM film thickness is220nm and the annealing temperature is120℃, the annealing time is10min. Under this condition, the highest PCE of2.6%can be reached.3. For comparative study, we added the AgNPs with different concentration and sizes into buffer layer to investigate the effects of silver nanoparticles on the performance of organic solar cells. Results indicate that the devices with30nm AgNPs in buffer layer show a better performance. When the concentration of silver nanoparticles is3mg/ml, the highest PCE of3.08%can be reached and the PCE enhancement of18.5%is achieved compared with the standard devices.4. Based on the above mentioned study, we insert an isolation layer between the doped buffer layer and active layer for separating silver nanoparticles with active layer and investigate the effects of the thickness of isolation layer on the performances of OSC. Result suggests that when the thickness of the isolation layer is10nm, the highest PCE of3.15%can be reached and the PCE enhancement of21.2%is achieved compared with the standard devices, and the PCE is further improved relative to the silver nanoparticles doped devices with no isolation layer.5. Finally we add the Ag@SiO2into OSC and investigate the effects of the concentration and position of Ag@SiO2on the performance of organic solar cells. Results indicate that the devices that one added with Ag@SiO2show a better performance. When the Ag@SiO2with the concentration of3mg/ml is introduced into the buffer layer, the highest PCE of3.23%and the PCE enhancement of24.2%compared with the standard devices can be reached. When the Ag@SiO2with the concentration of1mg/ml is introduced into the active layer, the highest PCE of3.22%and the PCE enhancement of23.8%compared with the standard devices can be achieved.