For more than half of a century, morphotropic phase boundary (MPB) in ferroelectric materials has drawn constant interest because it can significantly enhance the piezoelectric properties. However, MPB has been studied merely in ferroelectric systems, not in another large class of ferroic systems, the ferromagnets. In this Letter, we report the existence of an MPB in a ferromagnetic system TbCo2-DyCo2. Such a magnetic MPB involves a first-order magnetoelastic transition, at which both magnetization direction and crystal structure change simultaneously. The MPB composition demonstrates a 3-6 times larger "figure of merit" of magnetostrictive response compared with that of the off-MPB compositions. The finding of MPB in ferromagnets may help to discover novel high-performance magnetostrictive and even magnetoelectric materials.
High-efficiency hole transport layer
free perovskite solar cells (HTL-free PSCs) with economical and simplified
device structure can greatly facilitate the commercialization of PSCs.
However, eliminating the key HTL in PSCs results usually in a severe
efficiency loss and poor carrier transfer due to the energy-level
mismatching at the indium tin oxide (ITO)/perovskite interface. In
this study, we solve this issue by introducing an organic monomolecular
layer (ML) to raise the effective work function of ITO with the assistance
of an interface dipole created by Sn–N bonds. The energy-level
alignment at the ITO/perovskite interface is optimized with a barrier-free
contact, which favors efficient charge transfer and suppressed nonradiative
carrier recombination. The HTL-free PSCs based on the ML-modified
ITO yield an efficiency of 19.4%, much higher than those of HTL-free
PSCs on bare ITO (10.26%), comparable to state-of-the-art PSCs with
a HTL. This study provides an in-depth understanding of the mechanism
of interfacial energy-level alignment and facilitates the design of
advanced interfacial materials for simplified and efficient PSC devices.
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