Electrode Modification Effect On PbS Based Nanocrystalline Optoelectronic Devices

With the properties of spectral tunability and solution processability, colloidal quantumdots have been widely reported in the application of optoelectronic devices. In this utility, thetransparent conductive glasses including ITO and FTO are usually used as anode. But itssurface roughness has negative effects on carriers injection and extraction between the activelayer and the electrode. What’s more, the effects of moisture and oxygen penetration on thestability of device performance can’t be absolutely ignored. The interface modification onelectrodes are feasible strategy for optoelectronic device applications. In this dissertation, thediscussion on structure design and characteristic of the optoelectronic device based on PbSquantum dots are developed as follows.1. The devices with schottky junction were fabricated by using the PbS quantum dotssynthesized from hot injection method. The PEDOT:PSS and LiF were selected as modifiedlayer on the anode and cathode surface respectively. The influence of these two insert layerson rectifying and photovoltaic characteristics of the devices was characterized and discussed.After the modification of these layers, the device showed the improved ideal factor from6.6down to3.5and reduced conversion efficiency from10-5%to10-3%. The mechanism wasattributed to the change of work function and the suppression of surface defects. As a result,the barrier for carrier transport was reduced and carrier recombination was decreased.2. The heterojunction devices with structure of FTO/TiO2/PbS/Au were fabricated basedon the device with schottky junction. The influence of PEDOT:PSS and ZnO nanocrystallineinsert layers on device rectifying and photovoltaic characteristics were discussed. After themodification of these layers, the total resistance of the device was reduced from4.1×103to0.9×103and the ideal factor from7.54to2.56. The optoelectronic conversion efficiency ofthe device increased from0.02%to0.14%. These results were attributed to the effectiveelectrons transport by ZnO and effective collection of holes by PEDOT:PSS.3. The photovoltaic photodetector with schottky junction and heterojunction were bothfabricated with PbS quantum dots as an active layer. The heterojunction photovoltaicphotodetector exhibited better performance in term of photocurrent and response speed. Asfor the devices with ZnO nanocrystals and PEDOT:PSS as modification layer, the opticalresponse current was increased to0.28mA and the response time was down to0.07s. Thecurrent ratio was improved from1500to2500. The influence on the device performance wasprobably due to the reduced interface defects and increased photo-generated carriers.