Committee Chair: Christos Dimitrakopoulos
Hybrid organic-inorganic perovskites have emerged as one of the most promising technologies for the
future of solar energy due to their exceptional intrinsic photovoltaic properties. Planar p-i-n, or inverted, perovskite
solar cells that use low-temperature, solution-processable charge-transport layers have garnered much attention due
to their direct compatibility with flexible substrates and cost-effective high-throughput manufacturing. Nevertheless,
the inverted architecture has failed to repeatedly achieve the >20% power conversion efficiencies frequently attained
by its planar or mesostructured n-i-p counterpart (which generally has a charge-transporting layer requiring hightemperature
processing). Additionally, the perovskite active layer itself – regardless of the device architecture – has
poor stability in the presence of prolonged light exposure, high temperatures, and moisture.
In this study, we propose commercially viable strategies to improve the performance and stability of
inverted methylammonium lead iodide perovskite solar cells. First, we show that a simple two-step method
comprising evaporation-induced self-assembly of a lead iodide intermediate film coupled with the intermolecular
exchange of methylammonium iodide can yield high-quality methylammonium lead iodide perovskite films on nonideal
surfaces. Complete inverted devices with the perovskite active layer formed via this method outperformed
those devices with a perovskite layer produced using a conventional method. Second, we successfully replace the
commonly used but environmentally unstable calcium-aluminum electrode with a more stable silver electrode in
inverted perovskite devices via interfacial engineering without compromising device performance. By introducing
a solution-processable, thickness-tolerant n-doped zwitterionic fulleropyrrolidine interlayer between the phenyl-
C61-butyric acid methyl ester electron-transporting layer and the silver electrode, we successfully lower the work
function of the silver and improve charge transport, which led to an increase in device performance compared to
those devices with a calcium-aluminum electrode. Third, we examine the use of copper-based hole-transport
materials in inverted perovskite solar cells as a replacement for the more commonly used but less stable poly(3,4-
ethylenedioxythiophene) polystyrene sulfonate hole-transport material. We show that in most cases devices with a
copper-based hole-transport material outperform those with a poly(3,4-ethylenedioxythiophene) polystyrene
sulfonate hole-transport material due to the additive benefits from all relevant film/material properties (i.e.
morphology, optics, crystallinity/charge transport potential, and electronic band level alignment). Finally, we
present a procedure to effectively transfer monolayer CVD graphene onto a perovskite surface without damaging
or degrading the perovskite. We show that the incorporation of graphene significantly improves perovskite film and
inverted device stability in the presence of moisture and heat without sacrificing the overall device performance.
We hope that our efforts here aid in pushing the inverted perovskite solar cell closer towards commercialization.