Nanostructure Optoelectronic Devices And Their Interface Properties

Nowadays, optoelectronic devices are widely used in modern society and have played an important role in human’s daily life. Compared with conventional optoelectronic devices made with bulk materials, superior optoelectronic conversion properties of the emerging nanostructure optoelectronic devices attract extensively attention. The physical process of the optoelectronic devices is determined by interaction between photons and electrons, when power conversion occurs between photons and electrons, it is determined by generation, recombination, separation and collection process of the charge carriers. As dimensions of optoelectronic devices scaling down to nanoscale, plentiful of surface/interface in devices makes interface transport of charge carriers act as the dominate factor for device performance. Therefore, how to investigate nanostructure optoelectronic device interface in microscale, and understand the relationship between device performance in macroscale and interface related physical mechanism in microscale will be instructive and meaningful for further improve optoelectronic device performance.In this dissertation, we prepare different kinds of nanostructure optoelectronic devices, such as organic photovoltaic (OPV) devices, organic-inorganic hybrid photovoltaic devices and photodetectors, and investigate separation, recombination and collection process of charge carriers in these operando devices by scanning Kelvin probe microscopy (SKPM) and parameter measurement system. Finally, we optimize the device performance successfully according to the observed microscale mechanism.In chapter1, we briefly present the development of photovoltaic devices and photodetectors, and introduce the importance of shielding and guarding during nanostructure devices measurement. Then we introduce the development of SKPM and its application in nanostructure optoelectronic devices. In addition, the principle and application of dielectric force microscopy (DFM), which is established by our group, in one-dimension (1D) nanostructure is also shown.In chapter2, we directly visualize cross-sectional potential distribution in the operando OPV device by SKPM. Compared planar junction (PJ) device and bulk heteroj unction (BHJ) device, we make a correlation between surface potential distribution of device with its open-circuit voltage (Voc), short-circuit current (Jsc) and fill factor (FF). In our experiments, we unravel that optimized potential distribution of devices facilitate the separation and collection of photogenerated carriers.In chapter3, we compare conventional structure and inverted structure cross-section potential distribution, and found that interlayers can not only tune electrode work funtion, but also further impact device potential distribution and charge carriers collection process. Then we found both work function and surface morphology of ITO modified by interlayers are important factors to realize selective electrons collection, and demonstrate that alkali carbonates, not just cesium carbonate, are valid choices as the cathode interlayer in inverted OPV devices.In chapter4, we prepare Si nanowire (NW)/PEDOT:PSS hybrid photovoltaic device and ZnO NW/CuPc hybrid photodetector. We demonstrate that organic/inorganic interface passivates nanowire surface states effectively, and can improve photogenerated electron-hole pairs separation. Then we tune nanowire surface states deliberately, and found that directly and indirectly recombination happen during collection process of photogenerated charge carriers. Although charge carriers recombination impairs power conversion efficiency of photovoltaic device, it accelerates photoresponse speed of photodetector. Thus how to surpress or take advantage of surface state related recombination according to different condition, is a promising approach to improve hybrid optoelectronic device performance.