Preparation Of Radial Heterojunctions Based On Cu_2-xSe Quasi One-dimensional Nanostructures And Their Characterization

Copper selenide (Cu2-xSe) is a cationic defective p-type semiconductor material with a direct band gap 1.4 eV and an indirect band gap 2.3 eV at room temperature. It has been widely used in fields such as chemical sensors and optoelectronic devices due to its unique optical and electrical properties. It also has a potential application in the field of photovoltaics. Radial heteroj unction has an increasing application in the field of PV owing to the advantages of larger contact area and effective carrier separation. Here we were going to fabricate a radial heterojunction based on Cu2-xSe nanowires and therefore the photovoltaic devices based on it. The specific research works are listed as follows:1. Face-centered cubic Cu2-xSe nanowires were successfully synthesized through a mixing alkali method (a mixture of NaOH and KOH, Na/K atomic ratio was 48.5:51.5), using elemental seleniumas the selenium source and copper nitrate as the copper source. SEM images showed that the products were uniform nanowires with lengths up to 30 μm and a diameter of about 400nm. Electrical characterization showed that the conductivity of Cu2-xSe nanowires were about 0.5×10-2 S cm-1. The transport properties of Cu2-xSe FETs based on a single Cu2-xSe nanowire showed the p-type conductivity.2. Cu2-xSe/In2S3 radial heterojunction were fabricated through the solution-based coating method. Cu2-xSe nanowires were dispersed in deionized water. According to the surface functionalization route by the citrate, we prepared In2S3-coated Cu2-xSe nanowires. Then 20ml mmol/L In(NO3)3 solution and 20ml mmol/L Na2S solution were slowly added, respectively. TEM and element mapping showed that a layer of In2S3 was formed on the surface of Cu2-xSe nanowires. However, nanotubes were also observed. The reason may be that part of the Cu2-xSe nanowires have been cation exchanged with In3+. What’s more, EDS spectrum showed that there was small amounts of O elements in the product, which may arising from the In2O3 produced by In(NO3)3 hydrolysis.3. Cu2-xSe/In2Se3 radial heterojunction were fabricated through a solution-based cation exchange method. Cu2-xSe nanowires were dispersed in 25mL 1.5mmol/L In(NO3)3 solution with pH value 1.5 adjusted by acetic acid. The solution was stirred continuously and heated to 50℃, maintaining at that temperature for 5 h. TEM and element mapping showed that on the surface of Cu2-xSe nanowires generated a layer of In2Se3, indicated that Cu2+ ions in the surface of the nanowire had the effective cations exchange with In3+.4. In2S3 films were deposit by PLD method and Cu2-xSe/In2S3 radial heterojunctions were constructed.In2S3 films were deposited at different laser power using homemade In2S3 target from the highly purity In2S3 powder. XRD spectra and EDS spectrum analyzes indicated that the film was a body-centered cubic crystal system and In/S atomic ratio of 2/3. Electrical characterizations indicated that the film showed n-type conductivity. The film also had a significant photovoltaic effect with p-type silicon. The responsivity(R) and the detectivity(D*) are estimated to be 71.87A·W-1 and 1.39×1012 cm Hz1/2 W-1 based on Cu2-xSe/In2S3 film heterojunction, but no obvious photovoltaic effect was observed. Therefore, the device structure need to be further optimized.