Maria Chan

A fundamental study of the effects of grain boundaries on performance of poly-crystalline thin film CdTe solar cells

Poly-crystalline CdTe-based thin film photovoltaic devices have shown a great potential and are commercially used for large-scale energy conversion applications. Despite this success conversion efficiency of CdTe has achieved very minor improvements over the last 20 years. To overcome this stagnation and further drive cost-per-watt of the modules, better atomic-scale understanding of native dislocation structures and grain boundaries is needed. In this collaborative study we systematically investigate effects of grain boundaries using ultra-high-vacuum bonded CdTe bi-crystals with pre-defined misorientation angles.

Atomic Scale Study of Lomer-Cottrell and Hirth Lock Dislocations in CdTe

Many useful and also detrimental properties of solids can be traced back to the underlying structure of dislocations and their behavior. Their presence has been studied extensively studied in the context of crystal growth on lattice mismatched substrates and dislocations may significantly alter a material’s mechanical, thermal and opto-electronic properties [1]. Experimental knowledge detailing atomically resolved chemical structure of dislocation cores is highly desirable to advance fundamental understanding of these ubiquitous structures. In this study we present atomic scale analysis of two wellknown dislocations junctions in CdTe, the Lomer-Cottrell (L-C) and the Hirth lock. Despite being textbook examples of the lowest elastic energy stair-rod dislocations their atomic structure, in particularly in zinc-blende CdTe, were unknown. Stair-rod dislocations, usually identified in terms of their lack of mobility, may have important effects on the mechanical properties which raise concerns given the trend of continuous miniaturization of semiconductor devices. Furthermore, being pure-edge dislocations, L-C and Hirth locks are likely to be found in low-angle tilt grain boundaries.