Study On Organic Small Molecules Solar Cells Using Fe₃O₄as An Anode Buffer Layer

With the continuous development of science, the consumption of traditionalenergy is growing increasingly and people will run out of it eventually. It isimperative to explore a new energy, such as solar energy, which has become the mostpromising alternative energy source. Although inorganic solar cell has higher powerconversion efficiency, it can not be civilianized on a large scale because of its higherproduction cost and inflexibility. In contrast, for its advantages of lower productioncost, flexibility and simple production technology, organic solar cell has the potentialof large-scale civilianization. Therefore, the research and development of organicsolar cell has received extensive attention from the public.This paper firstly introduces the significance and progress of the research on thesolar cell，including the research status of organic small molecules solar cell. And theproduction condition and techniques of its devices is also presented in detail. TheCuPc/C60thin-film bilayer-heterojunction solar cells are fabricated by the way ofthermovacuum evaporation. And ferroferric oxide （Fe₃O₄） is inserted between thecopper phthalocaynine （CuPc） layer and the indium tin oxide （ITO） anode. Thestructure of the cell devices is ITO/Fe₃O₄/CuPc/C₆₀/BCP/AL. Then the performancesof the devices with buffer layer of different thickness are investigated, the results ofwhich are compared afterwards. The results shows that both the short-circuit currentdensity and the filling factor are enhanced by introducing a buffer layer of1nm Fe₃O₄to the cell, which leads to the increase of the power conversion efficiency. The deviceexhibts an open-circuit voltage （Voc） of0.344V, a short-circuit current density （Jsc） of2.52mA/cm2, and a calculated fill factor （FF） of49.6%. And the overall PCE for thiscell reaches to0.43%. The role of Fe₃O₄as a buffer layer played in improving theperformances of the device by using the ultraviolet photoemission spectroscopy （UPS）is studied in detail in this paper. In addition, when the incident light with its wavelength of470nm and the one of625nm irradiating the cell device, we simulateits light field distribution using a software. Then we compare the cell device intowhich1nm Fe₃O₄are inserted as a buffer layer with the one that are not, and findthat the light field distribution of the device change a little, which indicates that1nmFe₃O₄inserted into the device will not affect the performance of the device in theaspect of absorbing the light.The main performances of the cell device are affected by the work function andthe surface morphology of the film. In general, when the work function of the anodeincreases, the energy level between the anode and the CuPc will be reduced and thenthe efficiency of the collection of carriers increase. Subsequently, the open circuitvoltage of the cell device will be improved, the reason for which is mainly becausethat there exists interface dipole both in the interface between the anode and Fe₃O₄and interface between a buffer layer Fe₃O₄and CuPc. Just due to interface dipoleeffect, the energy level can be reduced. The change of the surface morphology of theanode will also have an effect on the performance of the cell device. And the rougherthe surface of the anode becomes, the denser the local traps on the surface will be.These local traps can attrach more charge carriers, and the surface of the Anode willcapture more holes. While, blocking the hole injection can reduce the open voltage.That is to say, the roughness of the surface of the anode obviously influences thepower conversion efficiency of the cell device. From the UPS （UltravioletPhotoelectron Spectroscopy）, after choosing the Fe₃O₄as the anode buffer layerenergy level between anode and CuPc reduces by0.2eV. According to the atomicforce microscope images, it is found that after Fe₃O₄is steamed on the surface of ITOthin film, the surface roughness of ITO decreases from1.79nm to1.45nm, while thesurface of the anode becomes flatter with the film resistance decreasing. Then the holeinjection will become easier. With the increase of the short circuit, the powerconversion efficiency is improved. Therefore, steaming Fe₃O₄on the surface of theanode as the anode buffer layer, the two factors affecting the efficiency conversionpower of the cell device has been improved.