Preparation Of Ag₂S And Investigation On Its Moisture Sensitive,photoelectric And Thermoelectric Properties

Silver sulfide（Ag₂S）,one of I-VI semiconductor materials,with a narrow band gap,has a wide range of applications in the fields of photoelectronics,catalysis and sensors.It is difficult to obtain high quality single crystal with large-size due to the fast nucleation rate,low crystal growth rate.The Ag₂S films prepared by various methods also have disadvantages,such as discontinuity,small crystal domain and low crystallization quality.The composition,structure,process and properties of materials are interrelated and affected each other.Low crystal quality Ag₂S limits and affects its practical application.In this paper,the preparation of Ag₂S was explored firstly,and then its humidity sensitive,photoelectric and thermoelectric properties were studied.The contents and results are shown as below.I.Preparation of Ag₂S.In this paper,Ag₂S were prepared by liquid phase method and solid-gas phase reaction method,respectively.It is found that Ag₂S can be grown in alkaline liquid phase of p H8 and the Ag₂S prepared by this method showed a three-dimensional network structure.Ag₂S product contained sulfur impurities,which can be removed by heat treatment.The growth temperature range of Ag₂S prepared by solid-gas phase reaction is between 250°C and 300°C.When the temperature is lower than 150°C,Ag films cannot be completely sulfurized.While when the temperature is higher than 400°C,discontinuous films are easily formed.II.Preparation and performance of Ag₂S humidity-sensitive device.Ag₂S-ethanol dispersions and PVP-Ag₂S-ethanol dispersions were dropped onto the interdigital electrode and dried naturally to obtain pure Ag₂S and PVP enhanced Ag₂S humidity-sensitive detectors,respectively.The results showed that the pure Ag₂S had poor humidity sensitive performance,which could be improved by adding PVP.The humidity sensitive performance of the device is the highest when the ratio of PVP:Ag₂S is 0.092%.III.Preparation and photoelectric properties of Ag₂S optoelectronic devices.Ag₂S photoconductance and thin film transistor were obtained by solid-gas reaction method.Ag₂S flexible electronic devices was obtained by the reaction between Ag NO₃ and Na₂S in solution.The results show that Ag₂S flexible electronic devices have good photoelectric response and short response time,and also found that Ag₂S photoconductive photodetector can be used to detect light intensity.Ag₂S base thin film transistors can be used to fabricate voltage-controlled current devices.IV.Preparation and thermoelectric performance of Ag₂S.The heterojunction was prepared by physical contact between p-type Cu₃P and n-type Ag₂S.Experimental data show that the heterojunction has good rectification characteristics.Compared with single Ag₂S and Cu₃P,the photoelectric response performance of the heterojunction is improved by about 6 times and about 647 times,respectively.A thermoelectric device is fabricated by connecting p-type Cu₃P and n-type Ag₂S with copper.Results showed that the resistance and voltage of the thermoelectric device would change with temperature.In summary,we found that the liquid phase method is a suitable method to prepare Ag₂S grain with small size.The disadvantage is hard to control accurately the proportion of reactants.The solid-gas phase reaction method can control the temperature to obtain continuous Ag₂S film,which is beneficial to improve the photoelectric performance of the device.Ag₂S has poor moisture sensitivity.The addition of hydrophilic polymer PVP can significantly improve the moisture sensitivity.Among different types of Ag₂S photoelectronic devices,the flexible Ag₂S device has the best photoelectronic performance.Other devices have the shortage of low optical response rate,which limits the application.Ag₂S/Cu₃P heterojunction devices show rectifier and thermoelectric properties.However,the preparation process simply affects the performance improvement of device.This paper provides a preference for the further study of the preparation and application of Ag₂S based devices.