EAGER: TDM Solar Cells: Collaborative Research: Monolithic 2-Junction Polycrystalline II-VI / Silicon Solar Cells

摘要非技术性的这项研究计划调查的战略，使太阳能电池显着更有效，提供了一条路线，以降低成本的太阳能电力。 该研究探讨了将两种商业上最成功的光伏（PV）技术-来自II-VI族半导体的碲化镉（CdTe）和晶体硅（Si）太阳能电池-结合在一起的障碍，以形成串联结构，其中II-VI太阳能电池沉积在Si电池顶部，其效率远远高于单独的电池。 研究的基础科学问题将直接实现只有两个电触点的高效多结电池，大大简化其制造并降低成本。 该计划在几个不同层面上造福社会。 在全球和国家层面上，高效太阳能电池技术将加速光伏发电的部署-今天占世界电力的1%以上-减少温室气体排放和伴随其他电力来源的国际安全问题，并增加美国和世界各地弱势群体的电力供应，同时创造高收入，美国的高科技工作。 在教育层面上，这项前沿研究为来自不同背景的学生提供了关键的科学培训，使他们获得进入快速增长的美国摄影师队伍所需的技能和经验。 该项目的目标是发展所需的科学理解，将II-VI顶部电池（例如具有15% Mg和1.75 eV带隙能量的CdMgTe合金）与晶体硅底部电池集成，形成只有两个端子的单片串联太阳能电池，以便于制造和用于光伏组件，目标效率超过28%。 该项目研究了五个关键科学领域：1）控制CdMgTe的体寿命和晶界复合的因素，因为它的带隙能量从CdTe的带隙能量增加; 2）由反转II-VI电池的通常生长顺序引起的半导体质量的变化; 3）顶部和底部电池之间的互连层的成分、界面性质和沉积条件; 4）化学上不同的顶部电池和底部电池之间的相互作用，其可能降低Si底部电池中的少数载流子寿命;以及5）用于展示具有28%的目标效率的原型2结CdMgTe/Si太阳能电池的集成技术，该目标效率远高于单独的任一种太阳能电池材料的最高效率。 区域1和2将在科罗拉多州立大学（CSU）进行研究，使用其单真空多源沉积系统制造的CdMgTe电池。 的CdMgTe吸收层的质量将通过时间分辨的光致发光和横截面扫描电子显微镜进行评估。 将主要通过标准电流-电压、量子效率和电容测量以及CSU开发的器件分析技术的应用来分析在p型CdMgTe上沉积有n型层的电池。 第3和第4区将在亚利桑那州立大学（ASU）学习。 不同的互连层的成分和组合将通过溅射，等离子体增强化学气相沉积，和原子层沉积，在亚利桑那州立大学建造的高寿命硅电池。 评估将侧重于电传输，光学透射率和高质量II-VI生长的适用性等关键指标。 由于与顶部电池生长相关的杂质的热预算和重组活动，在Si电池中的潜在变化将通过二次离子质谱，温度依赖性电流-电压和电感耦合载流子寿命测量来表征。 第五个领域，电池集成，将由两所大学共同完成，目标效率为28%，这将深刻影响太阳能发电在全球经济中的渗透。 然而，该项目的价值超出了光伏电池，揭示了低成本多晶半导体缺陷的基本原理，并提供了对其他应用的见解，例如在低成本硅上集成光发射器以实现高速计算。

AbstractNontechnicalThis research program investigates a strategy to make solar cells dramatically more efficient, providing a route to lower-cost solar electricity. The research examines barriers to combining the two most commercially successful photovoltaic (PV) technologies - cadmium telluride (CdTe) from the II-VI family of semiconductors and crystalline silicon (Si) solar cells - to form a tandem structure with the II-VI solar cell deposited on top of the Si cell for a much higher efficiency than either cell individually. The fundamental scientific issues investigated will directly enable high-efficiency multijunction cells with only two electrical contacts, greatly simplifying their manufacture and lowering costs. The program benefits society on several different levels. On a global and national level, the high-efficiency solar cell technologies would accelerate deployment of photovoltaics - which produce over 1% of the world's electricity today - reducing greenhouse gas emission and international security concerns that accompany other electricity sources, and increasing access to electrical power for disadvantaged populations in the U.S. and around the world, while creating high-paying, high-technology U.S. jobs. On an educational level, this cutting-edge research provides key scientific training for students from many backgrounds to give them the skills and experience necessary to enter the rapidly-growing U.S. photovoltaics workforce. TechnicalThe goals of the project are to develop the scientific understanding needed to integrate a II-VI top cell, for example the CdMgTe alloy with 15% Mg and 1.75-eV band-gap energy, with a crystalline silicon bottom cell to form a monolithic tandem solar cell with only two terminals for ease of manufacture and use in PV modules, and with a target efficiency over 28%. The project investigates five key scientific areas: 1) factors controlling the bulk lifetime and grain-boundary recombination of CdMgTe as its band-gap energy is increased from that of CdTe; 2) changes in semiconductor quality caused by reversing the usual growth order of II-VI cells; 3) composition, interface properties, and deposition conditions of the interconnection layers between the top and bottom cells; 4) interactions between the chemically different top and bottom cells that may degrade minority-carrier lifetime in the Si bottom cell; and 5) integration technology for demonstrating prototype 2-junction CdMgTe/Si solar cells with a target efficiency of 28%, well above the highest efficiencies of either solar cell material alone. Areas 1 and 2 will be investigated at Colorado State University (CSU) with CdMgTe cells made with its single-vacuum, multi-source deposition system. The quality of the CdMgTe absorber layer will be evaluated by time-resolved photoluminescence and cross-sectional scanning electron microscopy. Cells deposited with the n-type layer over the p-type CdMgTe will be primarily analyzed through standard current-voltage, quantum-efficiency, and capacitance measurements and the application of device-analysis techniques developed at CSU. Areas 3 and 4 will be studied at Arizona State University (ASU). Varying interconnection layer compositions and combinations will be deposited by sputtering, plasma-enhanced chemical vapor deposition, and atomic-layer deposition, on high-lifetime Si cells built at ASU. Evaluation will focus on the key metrics of electrical transport, optical transmittance, and suitability for high-quality II-VI growth on top. Potential changes in the Si cell due to the thermal budget and recombination activity of impurities associated with top cell growth will be characterized by secondary-ion mass spectroscopy, temperature-dependent current-voltage, and inductively-coupled carrier-lifetime measurements. Area 5, cell integration, will be accomplished jointly by the two universities with target efficiency of 28%, which would profoundly impact the penetration of solar-generated electricity in the global economy. The value of the project, however, extends beyond photovoltaic cells, shedding light on the fundamentals of defects in low-cost polycrystalline semiconductors, and providing insight on other applications such as integration of light emitters on low-cost silicon for high-speed computing.