环境友好型AgBiS2纳米晶异质结太阳能电池的制备与性能研究

The unpacked microstructure in the active layer caused by the broad size-distribution and organic ligands on surface of the pre-synthesized AgBiS2 nanocrystals (NCs), and energy band mismatch between the relevant interfaces are regarded as the bottleneck issues which can limit the achievement of high performance of the photovoltaic devices. Relevant studies have shown that the heterogeneous nucleation originating from the discrepancy of reactivity to anion S source between the two cation sources, Ag and Bi, is the main factor that can result in a broad size-distribution for AgBiS2 NCs, and there is no effective way to tackle this problem up to now. Our previous investigation has indicated that the “cation exchange mechanism” gets involved in the process of synthesizing AgBiS2 NCs. Accordingly, it can be deduced that the heterogeneous nucleation could be avoidable in the reaction system based on the mechanism, which is expected to optimize the AgBiS2 NCs’ size and its size-distribution simultaneously. In this project, the emphasis will be put on studying the regulation of morphology (size and size-distribution) of the AgBiS2 NCs via “cation exchange mechanism” and the achievement of the full organic ligands exchange on the surface of AgBiS2 NCs without any residuals via “external field induced ligands-exchange strategy”, elucidating the regularities and rules when regulating the microstructure and the interfacial band level of the active layer based on AgBiS2 NCs, and disclosing the transport and recombination mechanism involved inside of the AgBiS2 NCs based heterojunction photovoltaics, which will provide the important scientific basis and theoretical support for development of environmental-friendly nanocrystals-based heterojunction solar cells with excellent performance.

预先合成AgBiS2纳米晶尺寸分布宽化和表面有机配体残留所导致活性层不致密及相关接触界面能带失配是限制其异质结光伏器件获得高性能的瓶颈。相关研究表明Ag、Bi阳离子源相对于S阴离子源反应活性不同造成的非均相成核是导致AgBiS2纳米晶尺寸分布宽化的主要因素，且目前尚无有效办法应对。我们前期研究发现合成AgBiS2纳米晶过程中存在阳离子交换机制，因此推测此机制可作为合成指导原则以避免反应体系中出现非均相成核，实现AgBiS2纳米晶尺寸大小及分布的并行优化。本课题通过对阳离子交换法调控AgBiS2纳米晶形貌（尺寸大小及分布）和外场诱导配体交换法实现纳米晶表面有机配体无残留交换工艺的研究，阐明AgBiS2 纳米晶活性层微观结构及接触界面能级调控规律，揭示AgBiS2纳米晶异质结光伏器件内部载流子输运、复合机制，为高效环境友好型纳米晶光伏器件研究开发提供重要的科学依据和理论支撑。

AgBiS2纳米晶由于环境友好、空气稳定、高效能、兼具溶液制备及后期处理等优点，被认为是构建下一代薄膜太阳能电池潜力材料之一。本项目着重研究了以RoHS为框架下溶液法合成AgBiS2纳米晶的工艺流程，制备出尺寸大小及分布可调控的目标材料；并以巯基丙酸为小分子钝化剂实现合成后期对纳米晶表面的重新修饰钝化。而后，通过优化AgBiS2纳米晶液相离心浇筑成膜工艺，实现了纳米晶在指定基底上快速构建具有微观结构致密性的薄膜，提升薄膜电学性能。在此基础上，通过与ZnO纳米晶电子传输层组合构建n-i-p型正置薄膜太阳能电池，电池性能较传统经由LBL制备的AgBiS2纳米晶有源层电池提升了17.89%，效率达到了4.48%；同时，项目还对器件结构进行重新探索，合成了胶体稳定良好的MZO和NiOx纳米晶，并以旋涂成膜的方式分别制备电子传输层和空穴传输层，与浇筑的AgBiS2纳米晶薄膜组合构建p-i-n型反置薄膜太阳能电池，实现了器件的全无机化。得到的电池性能由于界面能级的优化，效率较正置器型有进一步提升，效率可达4.61%。纵观上述研究，单以电池效率为指标仍然有较大提升空间，但所获这些结果对于构建高效太阳能电池，提高光电转换效率具有重要的指导意义。