Tuning Photoelectronic Properties Of Sb₂Se₃ Thin Films

As a stable chalcogenide compound semiconductor,antimony selenide(Sb₂Se₃)has attracted much attention in the field of optoelectronic devices with the advantages of low toxicity,low cost,abundant raw materials,low crystallization temperature and large light absorption coefficient.In photovoltaic devices,with the implementation of carbon peaking and carbon neutral requirements,the development of low-cost solar cell technology is becoming increasingly important as one of the main forms of primary energy;Due to the existence of moonlight,starlight,atmospheric glow in the dark night environment produced by the weak night sky radiation,and most of the energy of the night sky radiation is concentrated in the near-infrared band,the use of objects on the near-infrared night sky light reflection imaging become the most common means of micro-light night vision.For these reason,in this thesis,two typical optoelectronic devices,solar cells and near-infrared photodetectors,are used as the entry point for an in-depth study of Sb₂Se₃ film preparation,material properties,and device structures.Based on the structural characteristics of sensitized solar cells,the thesis innovatively introduced the successive ion layer adsorption and reaction method(SILAR)into the study of Sb₂Se₃ thin film preparation.Based on the study of microstructure and photovoltaic properties of Sb₂Se₃ thin films and optimization of interfacial characteristics,Sb₂Se₃ sensitized solar cell was successfully constructed with improved performance.It was found that the low coverage of Sb₂Se₃ film grown at the interstices and inside the titanium dioxide mesoporous layer(M-TiO₂)led to the direct contact between M-TiO₂and electrolyte solution.Such phenomenon subsequently reduced the charge transfer efficiency of the device.Meanwhile,the high density of intrinsic defect states in the M-TiO₂ layer could easily capture electrons and increased the chance of charge recombination.To address this problem,the thesis used TiCl₄ aqueous solution to surface treat the M-TiO₂ layer and found it was deposited as a thin TiO₂ layer on the surface of M-TiO₂ layer.Such treatment not only passivated the surface defects and reduced the charge recombination rate of the device,but also optimized the growth conditions of Sb₂Se₃ and improved the film coverage.By optimizing the growth parameters of Sb₂Se₃thin film prepared by SILAR method,the device photoelectric conversion efficiency was finally increased to 1.22%.Based on the above work,this thesis further introduced a Cd Se interfacial modification layer between M-TiO₂ and Sb₂Se₃.It was found that the introduction of Cd Se interfacial modification layer not only further passivated the interfacial defects of M-TiO₂ and reduced the charge recombination,but also formed a dipole layer with M-TiO₂,reduced the surface work function of M-TiO₂,improved the injection and transfer efficiency of photogenerated electrons.In addition,benefited from the specific light-absorbing property of Cd Se itself,the light absorption waveband was broadened and the device photoelectric conversion efficiency was increased to 1.96%.According to the performance requirements of near-infrared photodetector devices,high quality Sb₂Se₃ thin films were prepared by physical vapor deposition(PVD)method.Sb₂Se₃ near-infrared photodetectors with photoconductive structure and Sb₂Se₃/Bi₂Se₃heterojunction diode structure were developed.To address the problem of Se vacancies in Sb₂Se₃ films prepared by thermal evaporation and Si substrate corroded by Se vapor,the F plasma surface treatment of Sb₂Se₃ film was carried out.It is found that,on the one hand,F ions entered the interior of Sb₂Se₃ lattice with the form of Sb-F bonds and filled Se vacancies,thus enhancing the electrical conductivity of Sb₂Se₃ films;On the other hand,F plasma effectively coalesced the grain boundaries of Sb₂Se₃ films and improved the charge transfer efficiency.After the optimization of the F plasma processing parameters,the excellent photoelectric response characteristics were obtained:the responsivity of 35.42 A W^-1,the detectivity of 4.89×10¹¹ Jones,the external quantum efficiency of 5.06×10³%and the rise/fall time of 21.4 ms/22.1 ms.Although F plasma surface treatment has improved the photoelectric response characteristics of Sb₂Se₃ photodetectors,the device response was still slow,in fact,the most effective way to compensate for Se vacancies was to provide an excess of Se beam current during the film preparation process.On this basis,this thesis used sapphire as the substrate to grow Sb₂Se₃ thin films and compared the effects of C-and R-plane sapphire on the photoelectric response characteristics of the grown Sb₂Se₃ thin films.It was found that the Sb₂Se₃ films grown on both sapphire substrates exhibited polycrystalline characteristics and the differences in surface morphology and optoelectronic properties were not significant;Notbly,the intensity of the(120)diffraction peak of the Sb₂Se₃ films grown on the sapphire was greater compared with that of the Sb₂Se₃ films grown on the Si substrate.This reflected that the presence of microstructural features of[Sb₄Se₆]_n long chains stacked parallel to the substrate in the growth of Sb₂Se₃ films.Such phenomenon facilitated the electron transport parallel to the substrate direction driven by the bias voltage,resulting in a faster optoelectronic response speed with rise and fall time of the order of a hundred micrometers for both sapphire devices.Based on the study of photoconductivity properties of Sb₂Se₃ thin film,in order to further improve the photoelectric property of the device,a high quality Bi₂Se₃ thin film was in situ grown on the surface of Sb₂Se₃ thin film and the Sb₂Se₃/Bi₂Se₃ heterojunction photodetector was constructed.By analyzing the energy band structure near the heterojunction,it was found that the Bi₂Se₃/Sb₂Se₃ heterojunction exhibited a type-II energy band alignment,which provided the driving force for the spatial separation of photogenerated carriers.The measured photoelectric response characteristics of the Bi₂Se₃/Sb₂Se₃ heterojunction diode showed that the device was still capable of stable photogenerated current at 0 V bias,showing photovoltaic device characteristics.Under the irradiation of near-infrared light source at 870 nm wavelength,the excellent photoelectric response characteristics were achieved:the responsivity of 1.01 m A W^-1,the detectivity of 1.06×10¹⁰ Jones,photo-to-dark current ratio of 1.72×10³ and the rise/fall time of 28?s/155?s.