Mixed-halide perovskites (MHPs), such as methylammonium lead bromide−iodide, CH 3 NH 3 Pb(Br x I 1−x ) 3 (0 < x < 1), are very promising candidates for tandem solar cells and wavelength-tunable light-emitting diodes (LEDs) due to their tunable bandgaps. However, uniform MHPs undergo phase separation under visible light irradiation or an electric field, and the reason is still under debate. In this work, we report that the phase separation can be dramatically suppressed by oxygen passivation under light illumination. More excitingly, we observe that phase-separated MHPs can be recovered to their original uniform state in an oxygen environment. Theoretical calculations demonstrate that oxygen atoms can effectively passivate traps in MHPs and occupy halide vacancies, thus suppressing halide redistribution and phase separation. Our results show that with sophisticated trap passivation techniques, phase-stable MHPs are attainable.
Ion migration is a notorious phenomenon observed in ionic perovskite materials. It causes several severe issues in perovskite optoelectronic devices such as instability, current hysteresis, and phase segregation.Here, we report that, in contrast to lead halide perovskites (LHPs), no ion migration or phase segregation was observed in tin halide perovskites (THPs) under illumination or an electric field. The origin is attributed to a much stronger Sn-halide bond and higher ion migration activation energy (E a ) in THPs, which remain nearly constant under illumination. We further figured out the threshold E a for the absence of ion migration to be around 0.65 eV using the CsSn y Pb 1-y -(I 0.6 Br 0.4 ) 3 system whose E a varies with Sn ratios. Our work shows that ion migration does not necessarily exist in all perovskites and suggests metallic doping to be a promising way of stopping ion migration and improving the intrinsic stability of perovskites.
Ion migration is a notorious phenomenon observed in ionic perovskite materials. It causes several severe issues in perovskite optoelectronic devices such as instability, current hysteresis, and phase segregation.Here, we report that, in contrast to lead halide perovskites (LHPs), no ion migration or phase segregation was observed in tin halide perovskites (THPs) under illumination or an electric field. The origin is attributed to a much stronger Sn-halide bond and higher ion migration activation energy (E a ) in THPs, which remain nearly constant under illumination. We further figured out the threshold E a for the absence of ion migration to be around 0.65 eV using the CsSn y Pb 1-y -(I 0.6 Br 0.4 ) 3 system whose E a varies with Sn ratios. Our work shows that ion migration does not necessarily exist in all perovskites and suggests metallic doping to be a promising way of stopping ion migration and improving the intrinsic stability of perovskites.
Metal-halide perovskites (MHPs) have made incredible achievements in the past few years, especially in the area of perovskite light-emitting diodes (PeLEDs). Nevertheless, hole transport layers (HTLs) used in most highly efficient PeLEDs usually have low hole mobilities in the range of 10 −4 -10 −6 cm 2 V −1 s −1 , much lower than that of MHPs, resulting in severe roll-off and low radiance of the devices. Here, methylammonium lead iodide (MAPbI 3 ) is successfully deposited on top of methylammonium lead chloride (MAPbCl 3 ) using orthogonal solvent to form heterojunction PeLEDs (HJ-PeLEDs). Due to the high hole mobility of MAPbCl 3 ≈42 cm 2 V −1 s −1 , the HJ-PeLEDs exhibit a peak external quantum efficiency of 10.7% and a high radiance of 157 W sr −1 m −2 at a low applied voltage of 3.9 V. Furthermore, the large-area (28 cm 2 ) HJ-PeLEDs made by blade coating shows a uniform and high radiance of ≈180 W sr −1 m −2 . This work provides a novel strategy to fabricate bright and large-area PeLEDs to meet the requirements of commercial applications.
Metal halide perovskites (MHPs) have been in the spotlight of the solar cell community in recent years due to their rapid increase in power conversion efficiency. The certified power conversion efficiency of perovskite solar cells (PSCs) has reached a high value of 25.5%, closing to its Shockley–Queisser limit and approaching that of crystalline silicon solar cells. However, it has been acknowledged that ion migration, an intrinsic property of MHPs causing many undesirable changes in PSCs, such as large current-voltage hysteresis curves, poor stability, low conductivity, phase segregation, etc., leads to PSCs degradation. In this chapter, we review ion migration in PSCs. We will cover topics including ion migration species in MHPs, ion migration channels, the factors that influence ion migration, and the effect of ion migration on perovskite solar cells, as well as strategies to suppress ion migration.
Perovskite light-emitting diodes (PeLEDs) show great
potential
in display and lighting because of their tunable wavelength, narrow
emission bandwidths, and high color purity. Currently, the external
quantum efficiency (EQE) of red and green PeLEDs has reached >23%.
However, yellow PeLEDs are still rarely reported because of phase
separation in mixed-halide perovskites and the coexistence of multiple
phases in quasi-two-dimensional (quasi-2D) perovskites L2A
n–1B
n
X3n+1 (n = 1, 2, 3,
...), where L is a bulky organoammonium ligand. Here, we fabricate
stable yellow PeLEDs by manipulating the phase distribution and incorporating
rubidium cations (Rb+) in quasi-2D perovskites. The transient
absorption results confirm that alkylammonium ligand butyl ammonium
(BA) has a narrower phase distribution than phenylethyl ammonium (PEA)
in the quasi-2D perovskites, resulting in a more blue-shifted emission
peak. We further incorporate a proper molar ratio of Rb+ in the (BA)2CsPb2I7 perovskite
to blue-shift the emission peak to the yellow range. Finally, the
yellow PeLEDs exhibit an EQE of 3.5%, and the stable emission peak
is located at 595 nm. Our work provides a useful approach for the
fabrication of highly efficient and stable yellow PeLEDs.
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