Research On The Fabrication And Properties Of Organic Photovoltaic Devices Based On ZnO

Organic photovoltaic （OPV） devices have attracted much interest due to their advantagesof light weight, low cost, and mechanical flexibility, which give a promise for industryproduction. However, the short life and poor stability of OPV devices are still the seriousproblems confining their development. Using an inverted structure is an approach to alleviatethis problem.The main objective of this thesis is to study the fabrication and properties of organicphotovoltaic devices based on ZnO. The main achievements obtained are summarized asfollows:Firstly, ZnO nanoparticles films were prepared via sol-gel process and incorporated intoinverted organic photovoltaic devices with a structure of ITO/ZnO/P3HT:PCBM/MoO3/Ag, inwhich ZnO film serves as an electron selective layer. The effects of annealing temperature ofZnO film on the device performance are investigated. When the annealing temperature is 300oC, a well-arranged ZnO thin film is obtained, and the optimized device has the PCE of 2.82%.This improvement can be attributed to the enlarged ZnO/active layer interfacial area andbetter energy band matching which causes an efficient electron extraction and a decreasedinterface energy barrier. At particularly high annealing temperature, dramatically increasedsheet resistance of ITO is found to cause PCE deterioration. Our finding indicates that it ishighly important to investigate both morphology and electrical effects for understanding andoptimizing OPV performance.Secondly, different concentration of AL³⁺doped ZnO nanorods （0 at.%, 0.5 at.%, 1.0 at.%and 1.5 at.%） were fabricated via hydro-thermal method. The ZnO nanorods were orderlyarrayed and well crystallined. As the AL³⁺doped concentration increasing, the conductivity ofZnO improved and the electron transfer between donor and acceptor became faster. AL³⁺doped ZnO nanorods were incorporated in the organic photovoltaic devices as both cathodeand electron conductive layer, the optimized device （0.5 at. %） shown 30% higher Jscand50% higher PCE compared to the device without AL³⁺doped.Thirdly, we further investigated the photoelectric properties of different concentration ofAL³⁺doped ZnO nanoparticles （0 at.%, 0.5 at.%, 1.0 at.% and 1.5 at.%）. The analysis indicatedthat the inappropriate annealing temperature resulted in the precipitation of Al atoms. Becauseof the accumulation of Al atoms at the interface, the surface energy of ZnO has been increased,which disturbs the directional transfermation of electrons. Furthermore, the surface of ZnObecomes rougher after AL³⁺doped, lead to a poor contacted interface between ZnO and activelayer. Therefore, the organic photovoltaic devices with AL³⁺doped ZnO nanoparticles did notget the desired performance.