Silver Nano-particle Surface Plasmon Enhanced Organic Solar Cell Research

In recent years, the study of organic solar cells has attracted much interest and obtained great achievements due to their low cost, easy of fabrication, and procession temperatures which are suitable for fabrication onto lightweight plastic substrates. However, due to the thin film structure of organic solar cells, light absorption efficiency is really low. The low light absorption efficiency is the main obstacle to improve the energy conversion efficiency of organic solar cells. Light trapping is particularly critical in such thin films solar cells in order to increase light absorption and hence cell efficiency.It has been proved that surface plasmons response on metal nanoparticles can increase the spectral response of thin films solar cells. In the paper, according to the progress of current research and laboratory conditions, we focused on the study of the optical property of Ag island films and its enhancement of light absorption efficiency in organic thin films.Firstly, we fabricat Ag island films using DC magnetron sputtering, and then, from the analysis of absorption spectrum of them, we initially determine some deposition parameters, such as deposition time and deposition power. And then on the basis of them, We experimentally and theoretically investigate the effect of substrate temperature on the morphologies and optical properties of the silver island films. The film prepared at 200℃exhibits a surface plasmons resonance peak around 500 nm where the most solar energy lies in. The morphologies of the films were characterized by atomic force microscopy (AFM), we notice that, at low temperature, below 200℃, as the substrate temperature increase, the sizes of nanoparticles decrease accompanied by an increasing density, but when the substrate temperature is up to 300℃, nanoparticles with larger in-plan (X-Y) dimensions are formed, and the density decreases. The film prepared at 200℃is estimated to have the most potential for harvesting solar energy.Secondly, to verify our inference in the first chapter, we fabricated schottky-type solar cells using copper phthalocyanine (CuPC) as active material which was sandwiched between the ITO electrodes which were modified by Ag island films and Ag electrodes. The thickness of CuPC and Ag electrodes were 100nm and 50nm respectively. We find that the addition of Ag island films lead to increased optical absorption and greatly affected the photosensitivity and IV characteristics of the devices. The open circuit voltage and short circuit current of the devices modified by Ag island films, which were prepared at room temperature,100℃and 300℃, significantly decrease compared with that of the non-modified device.The open circuit voltage of the device modified by Ag island film prepared under 200℃decrease slightly, but the short circuit density of it reaches 1.3 times as large as that of the device without modification.