新型层状铜基硫族光电化合物的合成和剥离及其光伏器件的基础研究

Graphene analogues of layered metal dichalcogenides were extensively investigated due to their unique physical properties. However, photovoltaic materials with excellent performance, especially for p-type absorbers of CuInGaSe2 and Cu2ZnSnS4 are four-coordinated diamond like structure. Therefore, it is a potential research field to synthesize and exfoliate novel layered copper-based chalcogenides for fabricating photovoltaic device via assembling layer by layer the exfoliated nanosheets of copper-based chalcogenides. The following contents will be researched to aim at the above problems in the proposal: (1) Novel layered copper-based chalcogenides are synthesized via low temperature thiourea solvothermal method or low melting point flux solid reaction method before the crystal structures of the materials are characterized. (2) The layered copper-based chalcogenides with excellent photovoltaic perfomance are selected and exfoliated to form two-dimensional crystals according to their absorption coefficient，band gap (Eg) and mobility. (3) The layered anisotropic two-dimensional crystals are dissolved into organic solvent with suitable density and polarity to assemble photoelectric thin films. (4) The matched n-type semiconductors are selected according to band gap of the p-type photoelectric thin films. Several main problems, including the electron-hole (e-h) separate, e-h recombination and charge collection, need be researched for fabricating prototype device and testing their photovoltaic performance. Two to three novel assembled photoelectric thin films will be found for acquiring photovoltaic devices with excellent performance.

类石墨烯层状硫化物因具有独特物理性质被广泛关注。然而，在光伏工业应用中优异的光电转换材料，尤其p型吸光材料CuInGaSe2和Cu2ZnSnS4，多为四配位 “类金刚石结构”。因此，新型层状铜基硫族化合物的合成、原子层的剥离、薄膜的组装及光伏器件化，是亟待发展的研究方向。本项目针对此类问题：(1)采取低温硫脲溶剂热法或低熔点助溶剂固相法，制备新型层状铜基硫族化合物，表征晶体结构；(2)根据吸收系数、禁带宽度(Eg)、迁移率等筛选出优异光电性能的化合物，进行二维晶体的剥离；(3)选择适合密度、极性的溶剂，利用二维晶体形状的各向异性，组装出光电薄膜；(4)结合p型光电薄膜的能带特性，选择功函数匹配的n型半导体; 对光生电子-空穴(e-h)分离，e-h的复合和电荷收集等关键问题进行研究，实现光电材料的原型器件化，评估其光电性能。通过项目实施，发现2-3种新型的光电薄膜，并获得性能优良的光电器件。

类石墨烯层状硫化物因具有独特物理性质被广泛关注。然而，在光伏工业应用中优异的光电转换材料，尤其p型铜硫化合物吸光材料，多为四配位 “类金刚石结构”。因此，新型层状铜基硫族化合物的合成、原子层的剥离、薄膜的组装及光伏器件化，是亟待发展的研究方向。本项目针对此类问题采取低温硫脲溶剂热法或低熔点助溶剂固相法，制备了K2Cu2GeS4、K2MSbS3等新型层状铜基硫族化合物，表征材料的晶体结构； 并根据吸收系数、禁带宽度(Eg)、迁移率等研究材料的光电性能，并进行二维晶体的剥离；选择适合密度、极性的溶剂，利用二维晶体形状的各向异性，组装出光电薄膜；结合p型光电薄膜的能带特性，选择功函数匹配的n型半导体; 对光生电子-空穴(e-h)分离，e-h的复合和电荷收集等关键问题进行研究，实现光电材料的原型器件化，评估其光电性能。项目实施过程中取得的重要结果有：通过第一性原理计算获得了K2Cu2GeS4的能带结构和态密度（DOS），其价带顶（VBM）接近C（1/2，1/2，0），而导带低（CBM）在G（0，0，0）。因此，K2Cu2GeS4作为一种典型的间接带隙为2.48 eV的半导体，与实验结果相吻合。有趣的是，在费米能级以上约1.32 eV处出现中间能带，这显著降低了带隙。K2Cu2GeS4的DOS和局域DOS可以得出以下结论：它的VBM主要由Cu-3d轨道和S-3p轨道支配，中间带主要由Ge-4s轨道和S-3p轨道组成。这与我们之前报道的Sn掺杂的CuGaS2和CuInS2相似，其中由于Sn和S价轨道之间的混合耦合效应而出现中间带。通过项目实施，完成了既定的项目目标，获得的结果为层状铜硫化合物及其光电转换器件研究和应用推广提供了重要的理论依据。