激光开膜的晶硅太阳电池栅极喷墨打印成形与Ag/Si接触机理研究

Fine line metallization plays a key role in silicon solar cell manufacturing. The inkjet metallization is considered as a next generation technology which could supersede the traditional screen printing. However, there are many difficulties in production of glass frit and good dispersion for ink system. Moreover, the process that glass frit etches the SiNx layer makes the formation of Ag/Si contacts more complicated. The mechanisms of inkjet metallization and Ag/Si contacts are therefore unclear. In our proposal, the laser selective ablation is introduced into the process of inkjet metallization which constitutes an innovative metallization process. To explore the mechanism of inkjet metallization, we propose the multiphase model based on lattice Boltzmann method. The new phenomena of fluid spreading, coalescence and coupled heat transfer generated by successive droplet impinging on the micro-groove is investigated. The relationship model between inkjet parameters and fluid morphologies is explored and established. Besides, in terms of Ag/Si contacts formation, we propose the multi-scale coupling model for handling the solid-fluid/fluid-sold phase change. The new characteristic of metal fluids flow in the micro-groove is investigated. The solidified microstructure evolution on the rough silicon substrate and the new mechanism of Ag/Si contacts are revealed. The scientific findings of our proposal could enrich the fundamental theory and method for solar cell metallization manufacturing and lay a solid foundation for new process development of solar cell inkjet metallization.

栅极制造是晶硅太阳电池制造的重要环节。喷墨打印成形被认为是替代丝网印刷的新一代栅极制造技术。然而，喷墨金属墨水中的玻璃粉配方在粉体制备和体系分散方面存在诸多困难，玻璃粉蚀穿氮化硅膜导致Ag/Si接触行为十分复杂，栅极成形及Ag/Si接触机理仍难以明确。本项目将激光技术引入到太阳电池栅极喷墨打印成形过程，是一种全新的工艺。在栅极打印成形机理方面，构建基于格子Boltzmann框架的多相流模型，研究多液滴连续撞击微凹槽成形的流体扩散、融合与耦合传热的新现象，建立打印工艺参量与成形形貌的参数匹配与关系模型。在Ag/Si接触机理方面，建立固液/液固相变多尺度耦合模型，探索金属液流在微凹槽内流动与输运的新特性，揭示金属液流在粗糙硅基底凝固的微观组织演化及Ag/Si接触界面成形的新机制。本项目的研究成果将丰富太阳电池栅极制造的基础理论与方法，为太阳电池栅极打印成形的新工艺开发奠定坚实的理论基础。

作为一种全新的栅极成形工艺，喷印技术能够直接在超薄硅片上精确打印出3D栅极金属化图案；栅极形貌可以按需设计，其非接触加工特征使得喷印技术更适合于薄片电池或柔性电池的栅极制造。本项目围绕晶硅太阳电池金属化栅极超细、大“高宽比”的制造难题，开展栅极喷印成形的基础理论和工艺研究工作。在基础理论研究方面，构建多物理场多尺度微流体模型，研究高速射流的喷射、颈缩、断裂成形的动态特性，探索压电/混合射流模式下的喷头内部温度场分布。提出了新的界面力格式，在两相界面运动和蒸发过程中精确描述纳米颗粒动态行为，获得了纳米银颗粒在相界面和沉积特征区域的成形形貌。在工艺研究方面，提出了面向晶硅绒面结构的交叉喷印成形方法，研究喷墨液滴间距、尺度和速度、沉积频率以及固化温度等工艺参量对成形结构的作用机理和影响规律，建立工艺参量与栅极成形形貌的关系模型，实现了高宽比≥0.6，栅极宽度≤40μm的超细栅喷印核心工艺，解决了多层喷印导致的液流局部堆积，以及栅极形貌不可控等工艺难题。研究热传导条件下的介尺度固液相变建模方法和金属液流凝固模型，探索金属液流凝固过程的形核产生、枝晶结构及微孔分布的相互作用规律，揭示金属液流在粗糙硅基底凝固的微观组织演化特征。