Perovskite
Solar Cells with Near 100% Internal Quantum
Efficiency Based on Large Single Crystalline Grains and Vertical Bulk
Heterojunctions
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Abstract
Imperfections in
organometal halide perovskite films such as grain
boundaries (GBs), defects, and traps detrimentally cause significant
nonradiative recombination energy loss and decreased power conversion
efficiency (PCE) in solar cells. Here, a simple layer-by-layer fabrication
process based on air exposure followed by thermal annealing is reported
to grow perovskite films with large, single-crystal grains and vertically
oriented GBs. The hole-transport medium Spiro-OMeTAD is then infiltrated
into the GBs to form vertically aligned bulk heterojunctions. Due
to the space-charge regions in the vicinity of GBs, the nonradiative
recombination in GBs is significantly suppressed. The GBs become active
carrier collection channels. Thus, the internal quantum efficiencies
of the devices approach 100% in the visible spectrum range. The optimized
cells yield an average PCE of 16.3 ± 0.9%, comparable to the
best solution-processed perovskite devices, establishing them as important
alternatives to growing ideal single crystal thin films in the pursuit
toward theoretical maximum PCE with industrially realistic processing
techniques