EAGER: New interconnect for the perovskite-silicon tandem solar cell: optically transparent and electrically conductive multilayer film

太阳能电池是可再生能源设备的核心，用于收集太阳光。在太阳能电池的几种光吸收剂中，卤化物钙钛矿是一种新兴的高性能吸收剂。钙钛矿太阳能电池（PSC）的功率转换效率（PCE）越来越接近在商业市场中占主导地位的硅太阳能电池的功率转换效率。此外，PSC可以使用简单且廉价的合成工艺来制造。因此，PSC具有满足低成本和高效率发电的迫切需要的潜力。然而，由于理论限制，PSC的性能预计不会优于硅太阳能电池。由PSC和Si太阳能电池组成的叠层太阳能电池是克服这种理论限制的有希望的解决方案。PSC和硅太阳能电池的堆叠可以比PSC或硅太阳能电池更好地利用太阳能。串联电池的关键部件之一是放置在顶部PSC和底部Si太阳能电池之间的互连。良好的互连需要是导电的和光学透明的。广泛用作叠层太阳能电池的互连的单层氧化物半导体不能完全满足这些要求。本项目将对半导体和金属薄膜的多层进行综合研究，以满足对高导电性和光学透明性互连的需求。这种新型的多层互连将提高叠层太阳能电池的性能，加速净零经济的到来。从工程教育的角度来看，该项目的多学科方面，包括材料合成，基础科学和设备制造，将加强当前的趋势，要求未来的科学家和工程师发展综合知识和技能。通过该项目，本科生和研究生将在材料科学，电气工程和器件物理学领域进行培训。在不同的串联电池设计中，2端（2-T）单片串联电池提供了最高的PCE，因为这种设计通过减少接口数量来提高透光率并抑制寄生电阻。此外，2 T串联电池简化了器件结构，显著降低了生产成本。然而，当前的2-T叠层太阳能电池缺乏合适的互连件，而互连件应提供高电导率和光学透明度。本项目将通过开发半导体-金属-半导体（S-M-S）多层膜来满足这一需求。中心金属层的高电载流子浓度和半导体层的高迁移率将结合用于高导电性的互连而不降低透明度。该探索性研究的目标是1）发展对透明导电S-M-S膜中的半导体和金属层之间的物理相互作用的基本理解，2）设计新型S-M-S互连，其选择性地收集PSC -硅叠层太阳能电池中的光生电荷载流子，以及3）测试叠层太阳能电池中的新互连。为此，将对对称和非对称金属-半导体多层膜进行广泛的实验和理论研究，以了解电子能带结构和光干涉。该项目的成果（即高电学和光学性能的互连）将促进界面处的电子空穴复合，并以最小的界面反射率将入射光传输到底部Si太阳能电池。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

A solar cell is at the heart of renewable energy devices for harvesting sun light. Out of several light absorbers for solar cells, halide perovskite is an emerging one of high performance. The power conversion efficiency (PCE) of perovskite solar cells (PSCs) is getting close to that of silicon solar cells which are dominant in a commercial market. In addition, PSCs can be manufactured using a simple and cheap synthesis process. Thus, PSCs have a potential to meet an urgent need for low cost and high efficiency power generation. However, the performance of PSCs is not expected to excel that of silicon solar cells due to a theoretical limit. A tandem solar cell consisting of PSC and Si solar cells is a promising solution to overcome such a theoretical limit. Stacks of PSC and silicon solar cell can harness solar energy much better than either PSCs or silicon solar cells. One of key components of the tandem cell is an interconnect which is placed between top PSC and bottom Si solar cells. A good interconnect needs to be electrically conductive and optically transparent. A single layer of oxide semiconductor, which is widely used as the interconnect of the tandem solar cell, does not fully meet these requirements. In this project, comprehensive research on the multilayer of semiconductor and metal films will be performed to address such a need for the interconnect of high electric conductivity and optical transparency. The new multilayer interconnect will improve the performance of the tandem solar cells and accelerate the advent of net zero economy. From the viewpoint of engineering education, the multidisciplinary aspect of this project including materials synthesis, basic science, and device fabrication will reinforce a current trend to ask future scientists and engineers to develop comprehensive knowledge and skills. Though the project, both undergraduate and graduate students will be trained in the areas of materials science, electric engineering and devices physics.Among different tandem cell designs, 2-terminal (2-T) monolithic tandem cells offers the highest PCE, because this design promotes light transmittance and suppresses parasitic resistance by reducing a number of interfaces. In addition, the 2T tandem cell simplifies the device structure and significantly reduces the production cost. However, current 2-T tandem solar cells suffer from a lack of the suitable interconnect which should provide high electric conductivity and optical transparency. This project will address this need by developing the semiconductor-metal-semiconductor (S-M-S) multilayer film. High electric carrier concentration of the central metal layer and high mobility of the semiconductor layer will be combined for the interconnect of the high electric conductivity without decreasing the transparency. The objectives of this exploratory research are 1) to develop a fundamental understanding of the physical interactions between semiconductor and metal layers in transparent conducting S-M-S films, 2) to design a novel S-M-S interconnect which selectively collects photogenerated charge carriers in PSC – silicon tandem solar cells and 3) test the new interconnect in the tandem solar cells. For these purposes, there will be extensive experimental and theoretical research on symmetric and asymmetric metal-semiconductor multilayer films to understand the electronic band structures and the light interference. Outcomes of this project (i.e. the interconnect of high electric and optical performance) will facilitate the electron-hole recombination at the interface and deliver incident to the bottom Si solar cell with minimal interface reflectance.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.