In situ imaging of stacking fault removal during annealing of a CdTe solar cell

Stacking faults are ubiquitous in the CdTe photovoltaic absorber material. Although not detrimental to solar cell performance by themselves, they originate at grain boundary defect sites that act as charge traps, and stacking fault occurrence is thus indicative of the latter. Annealing in the presence of a Cl source is an established method for passivating these grain boundary defects and, in the process, removing stacking faults. The posttreatment of the absorber layer improves the solar power conversion efficiency by more than 300%. We propose to study the removal of stacking faults in situ during annealing by dark-field X-ray microscopy. The aim is to quantify the impact of Cl bonding at stacking fault-initiating defects at the grain boundaries on the kinetics of stacking fault removal. This will enable us to improve existing models of Cl activation, thereby enabling more efficient pathways for the passivation of grain boundary defects and, thus, more efficient CdTe solar cells.

堆垛层错（Stacking faults）在碲化镉（CdTe）光伏吸收层材料中普遍存在。尽管其本身不会对太阳能电池性能造成损害，但这类缺陷起源于充当电荷陷阱的晶界缺陷位点，因此堆垛层错的出现可作为后者（晶界缺陷）的表征指标。在氯源环境下进行退火是目前成熟的晶界缺陷钝化工艺，同时可在该过程中消除堆垛层错。该吸收层后处理可将太阳能光电转换效率提升300%以上。本研究拟采用暗场X射线显微镜（dark-field X-ray microscopy）对退火过程中堆垛层错的原位消除过程展开研究，目标为量化晶界处引发堆垛层错的缺陷位点上的氯键合行为对堆垛层错消除动力学的影响。该研究将助力我们优化现有氯活化模型，进而为晶界缺陷钝化提供更高效的工艺路径，最终实现性能更优异的碲化镉太阳能电池。