Abstract
AbstractOrientational manipulation of transition dipole moment (TDM) plays an important role in controlling the polarization of excited states in light emission as well as lasing actions. The present work discovers vertically aligned TDMs in hybrid perovskite films through angle‐resolved photoluminescence (PL) measurements, which show enhanced emission through the film edge. With increasing excitation intensity, the edge emission induced by these vertically aligned TDMs becomes dominant and eventually leads to amplified spontaneous emission (ASE) through the edge view. Meanwhile, polarized emission of both PL and electroluminescence (EL) provides further evidence for vertically aligned TDMs. Surprisingly, the degree of polarization (DOP) through the film edge is increased when grain boundary defects are passivated through either stochiometric engineering or self‐passivation by mobile ions under working conditions. With increasing DOP, ASE threshold of the perovskite film is reduced owing to enhanced collective behaviors of light‐emitting states. This work presents a useful method to manipulate TDMs in organic–inorganic hybrid perovskites.
Highlights
Orientational manipulation of transition dipole moment (TDM) plays an face engineering.[1,2,3,4,5,6,7] With the external important role in controlling the polarization of excited states in light emission as well as lasing actions
An effective approach for polarization control in light emission is to manipulate transition vated through either stochiometric engineering or self-passivation by mobile dipole moment (TDM), which is the elecions under working conditions
Mixed large/small grains are confirmed by scanning electron microscopy (SEM) images in Figure S2a (Supporting Information), which shows that micrometer-size large cubic grains are surrounded by around 100 nm small grains
Summary
We follow our previous recipe to develop the perovskite (MAPbBr3) films with mixed large/small grains by using onestep solution processing method onto the PEDOT:PSS substrate.[19,20] The resulting perovskites show X-ray diffraction (XRD) patterns with featured peak at 14.80 (corresponding to (100) plane) (Figure S1a, Supporting Information) and an optical bandgap of 2.28 eV (Figure S1b, Supporting Information), consistent with previously reported polycrystalline MAPbBr3 perovskites. At a constant bias of 3 V, IR gradually increases with time from the initial value 1.7 to over 6000 cd m−2 within 10 s (as shown in Figure S8 in the Supporting Information) This gradual increase of EL intensity suggests the self-passivation process that the grain boundary defects are slowly passivated during the device operation.[19] Simultaneously, the relative EL output I90/IR measured at polarization direction of 90° gradually increases and stabilizes after around 10 s, which is of the same timescale as self-passivation process. With increasing amount of MABr, PL intensity increases significantly (over 20 times enhancement), indicating the passivation effects of MABr. To exclude the possibility of morphological or structural changes that induce the PL enhancement, we have compared both SEM (Figure S9, Supporting Information) and XRD (Figure S10, Supporting Information) results of two selected perovskite films mixed with large/small grains. It indicates that polarizing excited states toward coherent interaction will lead to enhanced light amplification
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