The Growth And Application Of Metal Chalcogenide Thin Films By Polymer-assisted Deposition

Energy crisis and environmental pollution have become global serious problems in 21^st century.Utilization of the renewable energy?solar energy,hydrogen,etc.?is an effective way to solve these problems.Due to the excellent photoelectrochemical performance and physical-chemical properties,metal chalcogenide thin films?MCTF?are widely applied in the field of solar cell,photocatalysis,transparent electrode materials,and light emitting diode,and so on.Therefore,growth of MCTF thin films has been one of the hottest research topics.Up to now,some synthetic methods?based on hydrazine chemical solution approach,based on organic solvent?DMSO?chemical solution approach,sol-gel etc.?have been reported to grow MCTF thin films.However,toxic/hazard organic solvents or forming grain boundary limit the expansion of the above MCTF for the further applications.Accordingly,it is of great concern to develop an environmental-friendly and versatile approach to grow MCTF.Here we will present an aqueous based polymer-assisted deposition to fabricate the diverse materials of MCTF.Investigation finds the advantages for polymer-assisted deposition.Firstly,the strategy presents aqueous soluble polymer and metal salts as raw materials having non-toxic and erosive reaction.Secondly,the lone pairs on the nitrogen atoms of the polymer easily form the covalent complex with the most of metal ions for the stable precursor solution.It is noting that mixing of several metal precursor solutions can achieve a homogeneous multi-metal precursor at a molecular level,effectively hindering the formation of a second phase during the growth of multi-metal chalcogenide thin film.Thirdly,the modification of polymer's amino-groups could be designed to grow multifunctional compound thin films.Forthly,the homogeneous and stable precursor solution can grow high-quality thin films with large scale.Here,we will study the versatile strategy towards metal oxide and metal sulfide thin film.Specfically,we systematically explore the materials of the polymer-assisted deposition including metal oxide thin film,metal sulfide thin film,multi-metal sulfide thin film,doped metal oxide thin film and multifunctional compound thin films,which are potential for the application in the field of solar cell and photocatalysis.The main contents are as follows:1.It is expored that polymer-assisted deposition is a chemical solution strategy evolving from atomic layer deposition?ALD?and chemical vapor deposition?CVD?for the growth of thin film.The precursor formation process and decomposed process are well investigated for the polymer-assisted deposition approach.The decomposition temperature of the polymer directly influences the growth of thin films.Although there are a little different in the different atmosphere,but the polymer could be totally decomposed at around 500 ^oC.Investigation finds that the stable precursor solutioin at molecular level homogeneously controls metal ions alike atoms of ALD during the the growth of thin films.Meanwhile,the flowing gas works on the precursor film as same as the atmosphere of CVD.Therefore,the strategy ensures the growth of high-quality thin films.2.Experimetals demonstrate the polymer can be combined with most of metal ions to provides a versatile way to grow MCTF.The polymer-assisted deposition has been applied to grow a series of metal oxide and metal sulfide thin films.In details,the effect of spin-coated times and annealed condition on the thin film is investigated by the examples of SnO₂and ZnS thin films.The result shows the thickness of the thin films is related to the spin-coated times during the growth of SnO₂ thin film.However,the quality of the thin film is slight affected by spin-coated times.The resultant SnO₂ thin film is uniform and compact with high transparency under visible light?>93%for 200 nm thin film?.Meanwhile,the effect of heating rate and the heating span on the growth of ZnS thin film reveals that the precursor solution treated by rapid thermal process is helpful to obtain homogeneous and highly crystalline thin films.3.As it is well known,it is easy to form a second phase during the growth multi-metal chalcogenide thin film.Polyer-assisted depsotion provides a platform to grow multi-metals chalcogenide thin films because the multi-metal precursors at molecular level hinder the formation of a second phase.Herein,the polymer-assisted deposition is used to grow multi-metal sulfide thin film by the example of Cu₂ZnSnS₄?CZTS?thin film.The element composition of the CZTS can be accurately controlled by the molecular solution.Consequently,the bandgap of the CZTS thin films can be adjusted between 1.05 to 1.95 eV by substituting Se with S as well as Sn with Ge.The as-grown CZTSSe thin film exhibits p-type semiconductor properties with high carrier concentration(4.5×10¹⁶ cm^-3)and high carrier mobility?43 cm²/V·S?.Moreover,the CZTSSe thin film as an active layer of the thin film solar cell has a power conversion efficiency of 3.55%.4.According to the reports,oxidized metal nitride is a usual method to grow N-doped metal oxide.While polymer-assisted deposition not only can grow high quality MCTF but also can grow metal nitrade thin films.Herein,it achieves a nitrogen-doped metal oxide thin film by oxidizing the metal nitride thin film,which is grown by polymer-assisted deposition.N-doped Ti O₂ thin film is used as an example to study of the growth and properties about N-doped metal oxide.The high-quality TiN thin film is grown by polymer-assisted deposition and then the TiN thin film is oxidized at different temperature to obtain a serial of N-doped TiO₂ thin films.It is found that the thin film oxidized at 450 ^oC with 4.33%of N shows the strongest ferromagnetic features at room temperature.5.It is realized that multifunctional compound thin films can be designed by the amino-group of the polymer modified with the desirable materials.The TiO₂@CNTs and TiO₂-NiO thin film are ready to grow for photocatalysis.The TiO₂@CNTs thin films is desirable to integrate with different ratio of CNTs ratio by polymer-assisted deposition.The CNTs are embedded in TiO₂ thin film to realize the uniform,transparency and super-hydrophilicity.The photodegraded performance is excellent owing to the fast carrier transport in the TiO₂@CNTs thin film.It is noting that the TiO₂@CNTs thin film with 5%CNTs has the best photodegraded performance,which is nearly twofold to that of pure TiO₂ thin film.The TiO₂@CNTs thin film will be a good candidate to self-cleaning glass.In addition,polymer-assisted deposition is used to grow the p-type NiO thin film on the n-type TiO₂ array substrate to attempt a p-n junction.0.25 M,0.5 M and 1 M Ni²⁺of the precursor are deposited on the TiO₂ array to form TiO₂-NiO complex.Compared with TiO₂ thin film,the TiO₂-NiO complex has a four-times photoelectrochemical performance as the result of the effective separation of carrier and hole.On the other hand,the thin film grown on TiO₂ array is an important breakthrough to polymer-assisted deposition approach.It potentially provides an alternative approach to grown thin films on conformal or 3-D structures substrate.