We
report the double-edged-sword effect of the thiourea (a typical
Lewis base) additive for tailoring the trap state distribution of
perovskite polycrystalline films. Through the thiourea treatment,
the polycrystal grain size is greatly increased because of the reduced
crystallization activation energy, which, together with the surface
defect passivation, alters the density of the energetically “deep”
and “shallow” trap states in a trade-off manner. Based
on this finding and further photoelectric and spectral studies, the
nonmonotonic dependence of the photoluminescence intensity on the
thiourea concentration and the complicated time-resolved photoluminescence
behavior are excellently clarified. As a proof of concept, the photophysical
performance of perovskite polycrystals is optimized via a modified
Lewis base treatment by taking the proposed double-edged-sword effect
into account.
Constructing a two-and three-dimensional (2D/3D) heterojunction structure on the surface of a 3D perovskite film, termed 2D/3D engineering, is effective in elevating the stability of perovskite polycrystal-based photovoltaic and photoelectronic devices; however, it remains controversial whether this protocol is favorable or detrimental to the device performance. Here, we prepare a series of 2D/ 3D perovskite films by post-treating the perovskite polycrystalline film with different concentrations of phenethylammonium iodide (PEAI). Systematic spectroscopy and electrochemical studies illustrate that PEAI can penetrate the 3D perovskite network and eliminate the intrinsic trap states of perovskite polycrystals, while the 2D perovskite nanosheets enriched on the top of the polycrystalline film may introduce additional trap states, which manipulate the photoluminescence performance and dynamics of the as-prepared perovskite films in an opposite manner. Based on this finding, the strategy of optimizing the photophysical properties of the host 3D perovskite through 2D/3D engineering is elaborated, paving the way for fabricating high-performance and high-stability perovskite polycrystalline films.
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