Preparation Of SnO₂-based Transparent P-n Junction And Its Photoelectric Conversion

Transparent optoelectronic devices,which have high transparency and high photoelectric performance at room temperature,have been widely used in smart windows,energy materials and related fields.In particular,transparent p-n junction devices composed of oxides,which have excellent photoelectric conversion performance,can be widely used in transparent solar cells,photovoltaic greenhouses and so on.As one of the n-type oxide materials,SnO2 has become one of the most widely used transparent conductive oxides(TCO)due to its abundant resources,high transmittance and chemical stability.However,since the conductivity of the p-type oxides reported so far is still much lower than that of the n-type oxides,and how to improve the utilization of the light energy is still a current problem under the premise of ensuring transparency,which greatly limits the development and practical applications of the transparent optoelectronic devices.Therefore,how to improve the conductivity of the p-type materials and the light energy utilization of the transparent materials are the core researchs for preparing transparent p-n junctions with great photoelectric conversion performance.In this paper,n-type SnO2 is selected as the basic material to improve the utilization of the light energy by preparing different microstructures(films,nanowire arrays(NAs),nanosheet arrays(NSs))under the premise of ensuring intrinsic conductivity.And p-type oxides(SnO,Cu2O,NiO)whose electrical properties are matched with SnO2 are prepared to effectively construce transparent p-n junctions through various modifications.On this basis,the photoelectric conversion performance of the p-n junctions are improved by modification methods,such as ZnO quantum dots(ZnO QDs),N-doped,Tm-doped CeO2 nanoparticles(Tm:CeO2).The thesis is consisted of three parts listed as following:(1)Zn(CH3COO)2 was used as the zinc sources,and tetramethylammonium hydroxide(TMAH)was used as the alkaline environment to obtain ZnO QDs under stirring in a water bath at 30?.Subsequently,the SnO2 film and SnO film with good conductivity and transparency were obtained by controlling the magnetron sputtering parameters.And the ZnO QDs were introduced into the interface of the SnO/SnO2 p-n junction,and finally the SnO/ZnO QDs/SnO2 p-n junction film was obtained.The basic structure of the p-n junction is qualitatively characterized by XRD,SEM,TEM and other charecterization methods.The photoelectric conversion tests were carried out under a three-electrodel system using the silver film as the electrode.The results show that the introduction of the ZnO QDs improves the photoelectric conversion performance of the SnO/SnO2 p-n junction film by about 100 times under the premise of 75%transmittance.The reason is mainly that the ZnO QDs can provide a large amount of photogenerated electrons and construct effective photogenerated carrier transport paths.(2)Since SnO has the disadvantage of being easily oxidized,it is considered to introduce the relatively stable Cu2O as the p-type materials.In addition,flexibility is also one of the development trends of smart devices in the future,so this part is devoted to the research of flexible transparent optoelectronic devices.Firstly,the SnO2 seed layer was pre-sputtered on the surface of the polyethylene naphthalate film(PEN)flexible substrate,and the SnO2 NAs was obtained by hydrothermal methods using SnCl4-5H2O as the tin sources.On this basis,the N-doped Cu2O film can be controlled by magnetron sputtering methods by adjusting the N2/Ar flow ratio,and finally the N-doped Cu2O/SnO2 NAs p-n junction film was successfully constructed.The results of photoelectric conversion performance tests show that the photoelectric conversion performance of the N-doped Cu2O/SnO2 p-n junction film is about 1500 times higher than that of the undoped Cu2O/SnO2 p-n junction film under the condition of maintaining 80%transmittance.And the device exhibits excellent flexible stability.After 1000 bends,the photoelectric conversion performance of the device is still as high as 91%of the initial value.The reasons are attributed to the fact that N-doped can increase the band gap and the conductivity of the Cu2O,and the nanowire arrays can provide direct carrier channels and release interfacial stress.(3)Limited by the physicochemical stability of the materials and the working environment,this part uses the more stable NiO as the p-type materials and is modified with the Tm:CeO2.Among,Ce(NO3)3·6H2O was used as the cerium sources,Tm(NO3)3·6H2O was used as the dopants,and the Tm:CeO2 was synthesized in a water bath at 80?.The Sn(OH)2 NSs was hydrothermally deposited on the glass substrate,and calcined at 400? to obtain the SnO2 NSs.Then,the Tm:CeO2 was introduced into the SnO2 NSs,and the NiO film was deposited by magnetron sputtering to effectively construct the NiO/Tm:CeO2/SnO2 NSs p-n junction film.The results of photoelectric conversion performance tests show that the introduction of the Tm:CeO2 improves the photoelectric conversion performance of the NiO/SnO2 p-n junction film by about 9700 times with 85%transmittance.The main reasons are that the Tm:CeO2 with up-conversion fluorescence performance expands the spectrum utilization ranges,and the microstructure of the SnO2 NSs enhances the efficiency of the light utilization.