Design of Defect-Tolerant Materials for Photovoltaic Applications

What makes a good photovoltaic (PV) material? The emergence of hybrid halide perovskites as a class of PV absorbers has spurred researchers to reconsider conventional wisdom about this question. Prior to 2015, every research cell exceeding 20% efficiency had been composed of exclusively inorganic materials synthesized at extreme purity either from the melt or via vapor deposition. Hybrid organic-inorganic perovskites are fabricated via solution synthesis, leading to a microstructure riddled with defects, yet their device efficiency now routinely rivals that of conventional materials. How can such a “messy” material achieve such high performance?

The answer that has emerged to this riddle is the notion of defect tolerance: the idea that in certain materials, naturally abundant (i.e. low formation-energy) defects simply aren’t as detrimental to device performance as defects in materials like silicon or gallium arsenide. A detailed understanding of this phenomenon is vital to the future of PV materials design, especially given the continuing challenges of toxicity and instability of hybrid perovskite materials.

In this talk, I will discuss figures of merit for PV absorbers broadly and how defect tolerance factors in. I will outline contributions from myself and others in the evolving theory of the origins of defect tolerance as well as what questions remain unanswered. Finally, I will discuss approaches for accelerating the design and screening of novel PV materials, and the importance of tight connections between theoretical/computational and experimental work in this effort.