Unified theory for light-induced halide segregation in mixed halide perovskites

Abstract

Mixed halide perovskites that are thermodynamically stable in the dark demix under illumination. This is problematic for their application in solar cells. We present a unified thermodynamic theory for this light-induced halide segregation that is based on a free energy lowering of photocarriers funnelling to a nucleated phase with different halide composition and lower band gap than the parent phase. We apply the theory to a sequence of mixed iodine-bromine perovskites. The spinodals separating metastable and unstable regions in the composition-temperature phase diagrams only slightly change under illumination, while light-induced binodals separating stable and metastable regions appear signalling the nucleation of a low-band gap iodine-rich phase. We find that the threshold photocarrier density for halide segregation is governed by the band gap difference of the parent and iodine-rich phase. Partial replacement of organic cations by cesium reduces this difference and therefore has a stabilizing effect.

Enhancing the stability and crystallinity of CsPbIBr2 through antisolvent engineering

“…Moreover, a given spectrum would ''reset'' if the sample were stored in dark conditions. These observations are consistent with observations made by other authors and with the so-called ''Hoke Effect'' [44][45][46]. While more detailed explanations can be found in the paper by Hoke et al, the evolution of a PL spectra in a mixed halide perovskite under illumination can be explained by the segregation of different halide phases causing iodine-rich regions to be formed, which in turn are responsible for the lower energy emission.…”

All-inorganic perovskite quantum dot light-emitting memories

“…Clearly, under this forward bias operation, both the V RRAM (middle panel) and the P LEC (bottom panel) traces keep up well with the V in , demonstrating that our LEM can operate as fast as 5 kHz, at which the data stored in the LEM can be electrically read by the Device 2 and optically transmitted through the parallel light emission from the Device 1. As pointed out earlier that the speed of individual CsPbBr 3 QD-based LEC and RRAM depends strongly on the ion generation and movement in the perovskite QD active layer, the operation speed of our all-perovskite LEM could potentially be enhanced by improving the intrinsic transport properties of the perovskites 49 , 50 . The fast operation of our LEM remains if the polarity of the pulse voltage is reversed (see Fig.…”

Toward stable lead halide perovskite solar cells: A knob on the A/X sites components

“… (G) Mixing enthalpy and free energy of mixed I/Br perovskites in the dark. Credit adapted from ( Chen et al., 2021 ). …”

“…Chen et al. applied a unified theory to understand halide phase segregation in MAPb(I 1−x Br x ) 3 , CsPb(I 1−x Br x ) 3 , FAPb(I 1−x Br x ) 3 , FA 7/8 Cs 1/8 Pb(I 1−x Br x ) 3 and MA 7/8 Cs 1/8 Pb(I 1−x Br x ) 3 perovskites ( Figure 10 G) ( Chen et al., 2021 ). The calculated width of the distribution in mixing enthalpy for single A site perovskites showed an increasing tendency in the order Cs + -MA + -FA + of increasing cation size.…”