高度有序ZnO纳米异质结阵列的构筑、界面调控及其在太阳电池中的应用

The arrayed nanostructures are widely used to enhance the separation and collection efficiency of photo-generated carriers in the heterojunctional solar cells. However,the difficulties in the controllable fabrication for ideal arrayed nanostructures and the interface modulation in the nanoscale restricted their further applications. Aimed to resolve these problems, two kinds of ZnO arrayed nanostructures are proposed in this research project. Firstly, the large-scale and highly ordered ZnO nanodot arrays will be fabricated on the conductive glass substrate through the nanoimprint lithography (NIL). Subsequently, the ZnO nanowire arrays with controllable length, wire-wire distance and wire density will be obtained through the hydrothermal growth. The controllability benefits from the restriction effects of pre-formed ZnO nanodot arrays and the hydrothermal growth conditions. Secondly, we also plan to fabricate a large-scale ZnO network arrays using the versatile nanosphere lithography technique. After the fabrication of two kinds of ZnO arrayed nanostructures, the interfaces of both them will be modulated through the ion-exchange reactions to form type II core-shell heterojunctions. The stepwised energy alignment at the interface can eliminate the surface states and interface states effectively, which will ensure the effective separation and collection of photo-generated carriers. In order to further improve the absorption, noble metal nanoparticles will be introduced into two kinds of ZnO nanostructures. The fundamental researches on the nanoscale opto-electric separation and charge transport process between the type II heterojunctional interfaces will also be carried out. Such a research project is proposed based on our previous research works and the thoroughly literature investigations. Therefore, we think there will be a remarkable conversion efficiency improvement by introducing our new type ZnO nanostructure arrays in heterojunction solar cells.

阵列化纳米结构可以为异质结太阳电池中光生电子-空穴对提供分离界面并为载流子提供直接的传输通道而备受关注，然而理想的阵列化纳米结构和纳米尺度异质结界面通常难以构筑和调控。本项目提出利用微加工技术大面积构筑两类ZnO阵列化纳米结构：1）利用NIL构筑具有取向性的ZnO点阵结构，在生长位点、水热生长条件的限制和调控、取向诱导生长的多重作用下，构筑长度、间距和线密度可控的ZnO纳米线阵列；2）利用胶体球模板组装技术大面积构筑ZnO网格状阵列；通过离子交换反应在两类ZnO阵列结构表面构筑II型核-壳异质界面，界面处形成的连续可调的能级结构可实现光生载流子的高效分离和收集；引入贵金属纳米颗粒，利用其表面等离子体激元共振进一步提升其光吸收；对纳米尺度异质界面间的光电分离、传输过程及其物理机制进行研究；构筑基于表面等离子体激元共振增强型ZnO纳米阵列结构的高效异质结太阳电池。

本研究项目针对薄膜太阳能电池器件中普遍存在的光吸收效率和载流子捕获效率相互制约的矛盾，提出构筑阵列化的纳米结构并通过界面调控实现薄膜太阳能电池中载流子的高效分离和收集。在国家自然科学基金委员会的资助和支持下，依托该研究项目主要开展了（1）CIGS/CZTS吸收层材料的电沉积和磁控法制备及高效太阳电池的设计；（2）高度有序ZnO纳米线阵列和ZnO空腔结构的设计和构筑；（3）II型ZnO/ZnXCd1-xSe核壳结构的构筑及其光电特性；（4）等离子共振效应增效TiO2纳米棒阵列结构光伏器件的构筑；（5）纳米结构增效型薄膜太阳能电池的设计和构筑等五个方面的研究工作。在项目组全体成员的共同努力下，目前已可以很好的制备电池级铜锌锡硫（硒）（CZTS）及铜铟镓硒（CIGS）吸收层材料，基于磁控溅射法制备的CIGS薄膜太阳能电池其光电转换效率已达到13%以上，基于电沉积和磁控溅射法所制备的CZTS薄膜太阳能电池，光电转换效率已达到8%左右，接近此类方法所制备的CZTS器件最高效率。利用微纳加工技术成功制备了高度有序的ZnO纳米线阵列结构和ZnO孔洞结构，并将两种ZnO纳米结构引入到不同类型的薄膜太阳能电池器件中，使其光电转换效率得到较大幅度的提升；对ZnO纳米线界面进行修饰，构筑了II型ZnO/ZnXCd1-xSe核壳结构，从而增加其光吸收范围，将其利用在染料敏华太阳能电池中，其光电转换效率可以达到1.7%，短路电流7.15 mA/cm2，开路电压为570 mV；将金纳米晶引入到染料敏华太阳能电池中，可有效增加其短路电流密度（从7.788 mA/cm2提高到8.574 mA/cm2），整个器件的光电转换效率提高了4.2%；利用所构筑的有序纳米结构，将其利用在不同种类的薄膜太阳能电池中，使其光电转换能力得到较大幅度的提升。这些研究成果的取得为发展新型的纳米结构增效型薄膜太阳能电池提供了实验基础和新的研究思路。