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Abstract
Lead-based organohalide perovskites have recently emerged as arguably the most promising
of all next generation thin film solar cell technologies. Power conversion efficiencies
have reached 20% in less than 5 years, and their application to other optoelectronic
device platforms such as photodetectors and light emitting diodes is being increasingly
reported. Organohalide perovskites can be solution processed or evaporated at low
temperatures to form simple thin film photojunctions, thus delivering the potential
for the holy grail of high efficiency, low embedded energy, and low cost photovoltaics.
The initial device-driven "perovskite fever" has more recently given way to efforts
to better understand how these materials work in solar cells, and deeper elucidation
of their structure-property relationships. In this Account, we focus on this element
of organohalide perovskite chemistry and physics in particular examining critical
electro-optical, morphological, and architectural phenomena. We first examine basic
crystal and chemical structure, and how this impacts important solar-cell related
properties such as the optical gap. We then turn to deeper electronic phenomena such
as carrier mobilities, trap densities, and recombination dynamics, as well as examining
ionic and dielectric properties and how these two types of physics impact each other.
The issue of whether organohalide perovskites are predominantly nonexcitonic at room
temperature is currently a matter of some debate, and we summarize the evidence for
what appears to be the emerging field consensus: an exciton binding energy of order
10 meV. Having discussed the important basic chemistry and physics we turn to more
device-related considerations including processing, morphology, architecture, thin
film electro-optics and interfacial energetics. These phenomena directly impact solar
cell performance parameters such as open circuit voltage, short circuit current density,
internal and external quantum efficiency, fill factor, and ultimately the all-important
power conversion efficiency. Finally, we address the key challenges pertinent to actually
delivering a new and viable solar cell technology. These include long-term cell stability,
scaling to the module level, and the toxicity associated with lead. Organohalide perovskites
not only offer exciting possibilities for next generation optoelectronics and photovoltaics,
but are an intriguing class of material crossing the boundaries of molecular solids
and banded inorganic semiconductors. This is a potential area of rich new chemistry,
materials science, and physics.
[1
]Centre for Organic Photonics
& Electronics, School of Chemistry and Molecular
Biosciences,
and School of Mathematics and Physics, The University of Queensland,
Brisbane, Queensland, Australia 4072