CENTER FOR EXCTIONICS presents:
Perovskite Tandems: A Path Towards Stable 27% Efficiencies*
May 17, 2017 at 12 noon/RLE Haus room: 36-428
Axel Palmstrom
Stanford University
[
http://www.rle.mit.edu/excitonics/wp-content/uploads/2017/05/AlexP1-199x300…]
Hybrid lead halide perovskites are promising candidates for low cost, thin film light
absorbers; they have a tunable band gap and have demonstrated efficiencies as high as
22.1%. As such, these materials are of interest for wide-bandgap absorbers in tandem
photovoltaics. Hybrid lead halide perovskites are soft materials with rough surfaces and
are sensitive to temperature and oxidative conditions, making many deposition processes
incompatible with this material. Typical perovskite solar cells employ spin-deposited
organic selective transport layers and evaporated metal contacts on top of the perovskite
absorber. These organic selective transport layers have a few main drawbacks for tandem
solar cells: first, the rough perovskite surface requires thick organic layers for
complete coverage, resulting in significant optical losses, second, these organic
materials are incompatible with the types of sputter processes used to deposit high
quality transparent contacts (such as indium-tin oxide) and third, organic materials are
typically poor elemental diffusion barriers; such barriers are important for device
stability. We applied tin oxide by atomic layer deposition (ALD) as a dual-purpose layer
to achieve electron selectivity and sputter protection with high optical transmission in
monolithic perovskite/silicon and perovskite/perovskite tandem devices.
I look at methods to push perovskite tandem efficiencies to 27% and beyond through
targeted short circuit current density, fill factor and open circuit voltage enhancements
while maintaining a stable device architecture. I will focus on the perovskite-tin oxide
interface on a range of perovskite compositions. Here I investigate the role of organic
surface passivation layers and ALD processing conditions on perovskite degradation and
interface energetics, which ultimately affects device open circuit voltage, a key figure
of merit towards achieving stable 27% efficient devices.
Axel Palmstrom is a graduate student at Stanford University in the group of Stacey Bent
pursuing his Ph.D. in Chemical Engineering. He graduated with Highest Honors from the
University of California, Santa Barbara in 2012 with a B.S. in Chemical Engineering. His
work focuses on the study metal oxide thin films grown by atomic layer deposition for
applications in thin film photovoltaics, including electron and hole selective layers,
barrier layers and surface passivation.
*This talk is part of the Perovskites Seminar Series organized by Juan-Pablo Correa-Baena
from MIT's PV Lab and sponsored by the Center for Excitonics. For more info contact
Juan-Pablo: jpcorrea@mit.edu<mailto:jpcorrea@mit.edu>
The Center For Excitonics Is An Energy Frontier Research Center Funded By The U.S.
Department Of Energy,
Office Of Science And Office Of Basic Energy Sciences
Light refreshments will be served.