Organic–inorganic lead halide perovskites (OLHPs)
with the
general chemical formula of APbX3 have attracted wide interest
for their application in the optoelectronics field within the past
decade. Despite the performance breakthroughs enabled by modifying
A-site cations, a fundamental understanding of the mechanistic origins
is still largely neglected. Especially, the critical role of A-site
cations in modulating the physicochemical properties of perovskites
is challenging to reveal because the choice of A-site cations is limited
by the geometrical Goldschmidt tolerance factor. Herein, we for the
first time successfully incorporated two large A-site cations in the
lead halide cage by relaxing the tolerance factor in a 2D Ruddlesden–Popper
system, and we obtained two novel single crystals, namely, (PA)2(Gua)Pb2I7 and (PA)2(Ace)Pb2I7, where PA = n-pentylamine,
Gua = guanidine, and Ace = acetamidine. The sizes of Gua (278 pm)
and Ace (277 pm) are almost identical and thus enable us to individually
study the influence of other properties of the A-site cation on the
optoelectronics properties including the polarity, electron donating
abilities, etc. By combining with first-principles theoretical perspectives,
we deliver insights into the electronic and structural features of
perovskites associated with A-site electron donating properties. This
adds more versatility to the roles of the A site cations in OLHPs.