Preparation Of High Performance Of Nano-ZnO Layers And Its Application In Inverted Organic Solar Cells

In recent years, conventional energies are becoming less and less, and energycrisis is worse and worse. In order to solve this problem, developing new cleanenergies is necessary. The most methods to use solar energy are to directly convertsolar energy into electrical energy. Almost all the countries in the world gradually payattention to the solar cell research, and some countries gave much subsidy policy tosolar power. In recent years, solar photovoltaic industry has been rapidly developed.In the commercial solar cells market, inorganic crystalline silicon solar cells occupy adominant position for its high conversion efficiency and other advantages. Butinorganic crystalline silicon solar cells have some shortcomings, for example, highcost, complex technology, not easy to large scale production, environmental pollutionand so on. The above reasons limit its large-scale application. Compared withinorganic solar cells, organic solar cells take advantages of low cost, light weight,good flexibility and large areas printing. Organic solar cells are becoming a hotresearch direction in the world. But conventional organic solar cells are not stablebecause PEDOT:PSS as hole transport layer will corrode ITO and Al cathode is easilyoxidized. While in the inverted polymer solar cells, the stability will be improved byusing ZnO as the electron transport layer and Ag or Au as anode. So it is important toresearch ZnO and inverted organic solar cells.Based on above reasons, high performance ZnO nanometer thin films wereprepared and used in the inverted organic solar cells in this paper. The main content ofthis thesis are as following.(1) Three methods were used to prepare nanometer ZnO film. To characterize theadvantages and disadvantages of three methods, SEM, XRD, AFM, absorption spectra,fluorescence spectra and other techniques were used. The result shows that, comparedwith other two methods, low temperature hydrolysis is the best approach to prepareZnO film.(2) The results show that the ZnO films prepared at low temperature byhydrolysis process have antireflective characteristics with a certain thickness. And thebest anti-reflection efficiency is up to18%at472nm. Theoretical calculatedthicknesses of the films with anti-reflection agreed well with the experimental results.By using Tauc-Sounds formula and effective mass model of a ball type nanoparticle,the band gap of nano-ZnO was calculated. The theoretical band gap is in accord wellwith the experimental result.(3) Energy level model of ZnO relative to defects was used to explain thefluorescence characteristics of ZnO prepared at low temperature. (4) Inverted solar cells were prepared and characterized. The factors influencedthe efficiencies of the solar cells were investigated in the experiment, includingannealing temperatures of active layers and ZnO films, the thicknesses of ZnO films,the ratios between acceptor and donor and the thicknesses of the active layers. Theexperimental results showed that the performances of devices were obviouslyimproved by annealing the active layers at120℃. When the nano-ZnO layer wasannealed at500℃, the efficiency of the device was obviously reduced. The bestthicknesse of nano-ZnO thin films is within785nm. When the ratio betweenacceptor and donor ration is1:1(P3HT: PCBM=1:1) and the thickness of the activelayer is140nm, the performance of solar cell is the best. By optimizing thepreparation process, we obtained the highest efficiency of3.58%in the experiment.