钙钛矿/硅叠层电池隧道结及界面研究与调控

The bottleneck of PV conversion efficiency is the root cause of the development of its power generation market. The theoretical conversion efficiency of the perovskite / crystalline silicon tandem solar cells is pointed to 35.6%, which is expected to be the destructive strategy for the revolution of photovoltaic market. However, the champion cell efficiency is only 23.6% in small aperture area. The powerful protocol to approaching the theoretical one is the tunneling junctions between the top and bottom cells because it was still ignored at the start up stage of the whole development of the perovskite/crystalline silicon tandem solar cells. Moreover, most of researchers are inclined to bet on the amorphous silicon thin film based silicon heterojunction solar cells currently with high efficiency values, missing a rising and promising transition-metal-oxides based crystalline silicon heterojunction solar cells with huge potential. Combining that with perovskite, this project focuses on the study of recombination and transport behavious at the tunneling junction of that tandem cells as well as building of their physical models and modulating the performance of the tandem cells via variation of tunnel junction materials and structures. This study includes: (1) Interface engineering for novel single junction perovskite solar cells with high conversion efficiency and stability; (2) Light control scanning Kelvin probe in-situ reveals the carriers recombination and transport mechanism at the tunnel junction and interfaces; Design, realization and regulation of OMO (oxide - metal - oxide) tunneling junction structures (3) and TMO-TCO-MO (transition metal oxide - transparent conductive oxide – metal oxide) ones (4). Basing on this work, we aim to achieve high-quality perovskite / crystalline silicon tandem solar cells and related processes, which is expected to promote high conversion-efficiency photovoltaic technology and market of our country in the future.

光伏转换效率瓶颈是制约其在发电市场发展的根本原因。钙钛矿/晶体硅叠层电池理论效率可达35.6%，是有望实现光伏跨越式发展的重要技术，而当前最高效率仅为23.6%，填补这一缺口的关键就是顶底电池间的隧道结技术。本项目基于新兴而极具潜力的金属氧化物-晶体硅异质结电池与钙钛矿电池结合的思想，聚焦于其钙钛矿/晶体硅叠层电池隧道结载流子复合和输运的物理机制的研究，致力于确立隧道结物理模型、以及隧道结材料和结构对叠层电池性能调控的数据库。内容主要包括：（1）新型高稳定钙钛矿电池实现及界面工程；（2）光控Kelvin探针等技术原位揭示隧道结及界面载流子复合和输运物理机制；（3）OMO（氧化物-金属-氧化物）及（4）TMO-TCO-MO（过渡金属氧化物-透明导电膜-氧化物）隧道结设计、实现与调控。本课题的实施，将为获得高质量钙钛矿/硅叠层电池器件及工艺，进而为高效光伏技术创新发展和应用提供理论与技术支持。

本项目围绕叠层电池隧道结对光学和电学特性的需求，设计制备了MoO3-Ag-WO3等一系列OMO（氧化物-金属-氧化物），以及IZO/Ag:BCP/NiO等类OMO结构的复合薄膜，研究了其透过率和折射率匹配等光学特性、面电阻及载流子传输等光电特性，设计制备了基于这些材料的一系列半透钙钛矿电池。所获得的高质量半透钙钛矿电池同时具备高达43.7%的平均透过率（AVT）和18.19%的转换效率，为半透钙钛矿电池当前报道的最好性能指标之一。围绕空穴传输层NiOX的掺杂及梯度调控、电子传输层SnO2的掺杂及梯度调控，和钙钛矿上下两端面的界面修饰，开展了一系列的系统性研究。建立了以氧化镍为空穴传输层的反式钙钛矿光伏器件基准结构和基准工艺，同时获得22%的单结反式钙钛矿电池转换效率，以及标准太阳光强暴晒2034小时仅衰减10%的超长器件稳定性数据。并通过一系列表征手段实现原位和离位的界面分析，揭示了其影响钙钛矿电池界面载流子输运和复合的物理机制。依据折射率匹配、高低带隙匹配、顶底电池电流匹配等原则，对上述复合薄膜的各层材料进行大量的甑选调配，以此为隧道结，设计制备了大量的、不同技术体系组合的钙钛矿/晶体硅叠层电池器件，并进行了一系列的器件物理表征，研究了各种因素对隧道结载流子复合效率的影响。其中以IZO/1nm Ag：BCP/NiO的类OMO结构的复合薄膜为隧道结，获得认证效率25.15%的高质量两端口钙钛矿/硅叠层电池，以及27.59%的四端口钙钛矿/硅叠层电池。基于进一步优化的上述隧道结OMO组合，获得23.6%的世界纪录的钙钛矿/有机叠层电池。同时揭示了复合薄膜独特微观结构促使了隧道结内纵向载流子复合速率增强和横向载流子传输抑制的双重效果。本项目产生的一系列的研究成果为钙钛矿/硅叠层电池光伏技术未来产业化提供了系统的可靠数据、方案选择和设计思想。