3D Printing of Solar Cell Contacts with Metal Reactive Inks

目前的太阳能电池触点是通过丝网印刷银浆，然后在高温下将银粒子烧结在一起形成导电电极制成的。然而，高温烧结步骤成本高昂，与薄膜太阳能电池技术不兼容。一种解决方案是使用低温活性油墨。活性油墨打印在低温下反应的化学物质(而不是打印颗粒)，并可能产生具有良好导电性的致密材料。不幸的是，未优化的活性油墨往往会在印刷材料中产生高孔隙率。该奖项支持基础研究，使新型银活性油墨和铜活性油墨的开发成为可能，这种油墨可以打印出孔隙率非常低的导电材料。这些新型油墨可应用于光伏和低成本柔性电子产品。第一个研究目标是了解油墨组成(包括配体类型、反应物浓度和溶剂)对活性油墨的化学和流体性能的影响。正在研究的相关油墨特性包括反应活化能、阿累尼乌斯指前因子、汽化热、扩散系数、粘度和表面张力。通过实验测量配体类型(例如：[(NH_3)_2CH_3CO_2]-、[(NH_3)_2NO_3]-和2-氨基-2-甲基-1-丙醇)、反应物浓度(10µm o l/L到1 m o l/L)和溶剂类型(乙醇、水、甘油和2，3-丁二醇)的相关性质来实现这一目标。活化能、阿累尼乌斯指前因子和汽化热将使用差示扫描量热仪和热重分析仪测量；扩散系数将使用计时电流法和循环伏安法测量；粘度将使用MicroVISC流变仪测量；表面张力将使用定制测角仪测量。第二个研究目标是了解油墨组成和工艺参数对蒸发活性油墨液滴中化学势分布的影响。为了实现这一目标，将使用配备了传热学、计算流体力学、化学反应工程和粒子跟踪模块的COMSOL多物理进行模拟。这些模拟将预测随着油墨组成和工艺参数的变化，蒸发活性油墨液滴中的化学势分布。第三个研究目标是了解反应动力学对蒸发活性油墨液滴中颗粒成核和生长速率分布的影响。为了实现这一目标，将使用经典的成核理论来模拟粒子的成核和生长速率分布，其活化能取自文献。反应动力学将使用测量的反应活化能、测量的Arrhenius指数前因子和模拟的化学势分布来计算。一些预测结果将与实验观测结果进行比较。

Current solar cell contacts are made by screen-printing silver pastes and then sintering the silver particles together at high temperatures to form a conductive electrode. However, the high-temperature sintering step is costly and is not compatible with thin-film solar cell technologies. One solution is to use low-temperature reactive inks. Reactive inks print chemicals (instead of printing particles) that react at low temperatures, and can potentially produce dense materials with good electrical conductivity. Unfortunately, non-optimized reactive inks tend to produce high porosity in printed materials. This award supports fundamental research to enable development of new silver and copper reactive inks that can print conductive materials with very low porosity. These new inks can have applications in photovoltaics and low-cost flexible electronics.The first research objective is to understand the effect of ink composition (including ligand type, reactant concentration, and solvent) on the chemical and fluid properties of reactive inks. Relevant ink properties under investigation include reaction activation energy, Arrhenius pre-exponential factor, heat-of-vaporization, diffusion coefficient, viscosity, and surface tension. This objective will be achieved by experimentally measuring relevant properties as ligand type (examples: [(NH3)2CH3CO2]-, [(NH3)2NO3]-, and 2-amino-2-methyl-1-propanol), reactant concentration (10 µmol/L to 1 mol/L), and solvent type (ethanol, water, glycerol, and 2,3-butandiol) are varied. Activation energy, Arrhenius pre-exponential factor, and heat of vaporization will be measured using a differential scanning calorimeter and a thermogravimetric analyzer; diffusion coefficient will be measured using chronoamperometry and cyclic voltammetry; viscosity will be measured using a microVISC rheometer; and surface tension will be measured using a custom goniometer. The second research objective is to understand the effect of ink composition and processing parameters on chemical potential distribution in evaporating reactive ink droplets. To achieve this objective, simulations will be conducted using Comsol Multiphysics equipped with heat transfer, computational fluid dynamics, chemical reaction engineering, and particle tracing modules. These simulations will predict the chemical potential distribution in evaporating reactive ink droplets as ink composition and processing parameters are varied. The third research objective is to understand the effect of reaction kinetics on particle nucleation and growth rate distributions in evaporating reactive ink droplets. To achieve this objective, particle nucleation and growth rate distributions will be modeled using the classical nucleation theory with activation energies taken from the literature. The reaction kinetics will be calculated using the measured reaction activation energy, the measured Arrhenius pre-exponential factor, and the simulated chemical potential distribution. Some predicted results will be compared with experimental observations.