Preparation Of Selenide Semiconductors For Photoelectric Devices Applications

During the last half century,semiconductor technology has achieved rapid development as the core of modern high technology.Various new materials and functional devices based on semiconductor technology affect all aspects of our life.It is known that the fundamental research and application of semiconductor materials are the basis of developing semiconductor technology,which is also an important source of motivation and confidence for numerous scientific researchers.In this dissertation,two different selenide semiconductors with excellent properties are selected as our research targets,including the controllable preparation of materials and the exploration of applications as high performance photoelectric functional devices.Firstly,Sb2Se3 nanorods were synthesized via hot-injection method,and the biggest challenge of low conductivity of Sb2Se3 nanorods were overcomed successfully by forming semiconductor heterojunction and semiconductor doping.The high performance prototype photodetectors based on Sb2Se3 nanorods were constructed.Then the Sn-doped Sb2Se3 crystals with controllable electrical conductivity and photoconductivity were prepared by high-temperature melting process.Afterwards,the same technique was used to obtain Sb2Se3-based targets,which can be further used for the preparation of thin films by Radio Frequency(RF)magnetron sputtering.The quasi-homojunction Sb2Se3 thin film solar cells were also explored based on those high-quality thin films,which show high application potential.Moreover,the uniform γ-In2Se3 nanoflowers were also synthesized via the hot-injection method.In combination with the mature Si-based semiconductor technology,a high performance γ-In2Se3/Si heterojunction photodiode was fabricated for the first time.The obtained innovative research results are as follows:(I)The high-quality Sb2Se3 nanorods were successfully synthesized by a hot-injection method,the reaction temperature,reaction time and surfactants showed an important impact on the morphology and structure of the nanorods.The intrinsic resistivity of Sb2Se3 is as high as 106Ω·m,which greatly affects its practical applications.To overcome this challenge,two effective approaches have been developed.One was the forming of composites with a high conductivity second phase and the hybrid nanorods with Sb2Se3/AgSbSe2 heterojunction structure have been prepared accordingly.This interconnected heterojunction structure can significantly improve the electrical conductivity of the Sb2Se3 nanorods.The other approach was doping,where Sn was chosen as a dopant.With increasing Sn4+ doping concentration,the obtained(SnxSb1-x)2Se3 nanorods exhibit an improvement of electrical conductivity with several orders of magnitude.Finally,the as-synthesized Sb2Se3 nanorods,hybrid nanorods with the Sb2Se3/AgSbSe2 heterojunction structure and(SnxSb1-x)2Se3 nanorods were all used for fabricating prototype photodetectors.The results show that the Sb2Se3/AgSbSe2 heterojunction nanorod film photodetector with a remarkable response to visible light,and the calculated responsivity is about 4.2 times as much as that of Sb2Se3 nanorod film photodetector.Then the(SnxSb1-x)2Se3 nanorod film photodetector also exhibits remarkable responsivity and detectivity over a wide spectral range from ultraviolet to near-infrared.Overall,the Sb2Se3 nanorods with enhanced electrical conductivity show a higher application potential as highly efficient photodetectors.(2)(SnxSb1-x)2Se3(x=0.00,0.03,0.05,0.07,0.10)polycrystalline semiconductors were successfully prepared by using an effective high-temperature melting process.The(SnxSb1-x)2Se3 bulk crystal surface with chemical etching by NaOH solution clearly show micron-sized grains.EDS elemental analysis further reveal Sn-rich regions between the grain boundaries,indicating the existence of phase separation.With increasing Sn doping concentration,(SnxSb1-x)2Se3 crystals also exhibit a great improvement of electrical conductivity with several orders of magnitude due to much higher charge carrier concentration.The PEC measurement by using(SnxSb1-x)2Se3 crystals as working electrode show clear photoelectric response and the crystal are identified as p-type semiconductors.Notably,compared to pure Sb2Se3,the dark current density of a representative(Sn0.10Sb0.90)2Se3 is increased approximately by 10 times and the photocurrent density by approximately 14 times,indicating that Sn doping significantly improved the photoconductivity of the Sb2Se3 crystal.The band gap of the(SnxSb1-x)2Se3 crystals is 1.10 eV,which overlap well with the solar spectrum.Therefore,the(SnxSb1-x)2Se3 crystals have excellent electrical conductivity and photoconductive properties,combined with their easy and scalability synthesis features.These properties confirm the high application potential of Sn-doped Sb2Se3 for highly efficient photoelectric devices.(3)Four Sb2Se3-based targets with the chemical composition of Sb2Se3,Sb2Se3.3,(Sn0.1Sb0.9)2Se3 and Sb2(Se0.9I0.1)3 could be successfully prepared by high-temperature melting.Then the thin films were deposited by using RF magnetron sputtering.The as-deposited thin film showed amorphous nature,after a heat treatment at an approprite temperature,a high crystalline thin film composed of large crystal grains was obtained.The optical properties of the thin films were investigated systematically.It has been found that the crystallinity and the roughness are the main factors affecting the reflectance of the thin films.The band gap of the Sb2Se3 amorphous film is 1.64 eV,then turns to 1.28 eV for the crystalline film.In contrast,the value is close for Sb2Se3.3 thin film,however show slight decrease and increase for(Sn0.1Sb0.9)2Se3 and Sb2(Se0,9I0.1)3,respectively.The heat treatment temperature play an important role for determining the p/n type of the Sb2Se3 and Sb2Se3.3 thin films with a transformation from p type to n type with increasing temperature.Differently,all the(Sn0.1Sb0.9)2Se3 thin films show p type behavior and all the Sb2(Se0.9I0.1)3 thin films are n type.The PEC measurements by using Sb2Se3-based thin films as working electrode have obvious photoelectric response,also with the features of fast response and long-term stability.Accordingly,a novel quasi-homojunction Sb2Se3 thin film solar cell was firstly fabricated.The existence of p-n junction inside the device structure has been demonstrated.The thickness and the heat treatment temperature have a close relationship with the device performance.The highest conversion efficiency obtained in our work reaches already a highly interesting 2.65%.Importantly,it shows great application potential as high performance thin film solar cells.(4)An effective colloidal process involving the hot-injection method has also been developed to synthesize uniform γ-In2Se3 nanoflowers with single crystal phase.The systematic studies on the reaction time and reaction temperature reveal the growth mechanism of y-In2Se3 nanoflowers.Afterwards,an effective heterojunction photodiode formed by n-Si and γ-In2Se3 nanoflower film was fabricated for the first time.It is self-powered,with a very short response/recovery time(175/226 μs)and long-term durability,also displays a high responsivity and detectivity in a wide range of wavelength.These excellent properties indicate that the y-In2Se3/Si heterojunction photodiode is very promising to be used as a highly efficient photodetector.