Correlating Phase Behavior with Photophysical Properties in Mixed‐Cation Mixed‐Halide Perovskite Thin Films

Abstract

Mixed cation perovskites currently achieve very promising efficiency and operational stability when used as the active semiconductor in thin‐film photovoltaic devices. However, an in‐depth understanding of the structural and photophysical properties that drive this enhanced performance is still lacking. Here the prototypical mixed‐cation mixed‐halide perovskite (FAPbI3)0.85(MAPbBr3)0.15 is explored, and temperature‐dependent X‐ray diffraction measurements that are correlated with steady state and time‐resolved photoluminescence data are presented. The measurements indicate that this material adopts a pseudocubic perovskite α phase at room temperature, with a transition to a pseudotetragonal β phase occurring at ≈260 K. It is found that the temperature dependence of the radiative recombination rates correlates with temperature‐dependent changes in the structural configuration, and observed phase transitions also mark changes in the gradient of the optical bandgap. The work illustrates that temperature‐dependent changes in the perovskite crystal structure alter the charge carrier recombination processes and photoluminescence properties within such hybrid organic–inorganic materials. The findings have significant implications for photovoltaic performance at different operating temperatures, as well as providing new insight on the effect of alloying cations and halides on the phase behavior of hybrid perovskite materials.

Low-Temperature Induced Enhancement of Photoelectric Performance in Semiconducting Nanomaterials

“…As shown in Figure 3 a, a significant blueshift of absorption and a widened bandgap is observed in the p-Si/n-ZnO heterojunction when starting temperature declines [ 113 ]. However, as shown in Figure 3 a,b, for both photoluminescence (PL) spectra and absorption spectra, the (FAPbI 3 ) 0.85 (MAPbBr 3 ) 0.15 perovskite thin films show a red-shift trend [ 39 ]. Thus, a declined optical bandgap at low temperature is calculated.…”

“…There are also investigations focusing on the dynamic theory of phase transition [ 168 , 169 , 170 ], not discussed in detail here. In response to in-depth knowledge of the interplay between low-temperature-caused structure transition and optoelectronic properties, Greenland et al verified the dominated phase of mixed-cation mixed-halide perovskite (FAPbI 3 ) 0.85 (MAPbBr 3 ) 0.1 at different temperatures and observed sudden changes in absorption [ 39 ] and carrier density, as well as the recombination rate at the corresponding phase-transition temperature, shown in Figure 7 c. Lou et al reported the temperature-dependent spectral response of FAPb(Br 0.4 I 0.6 ) 3 . They also reported that β-phase, which possess fewer defects and a narrower band gap, appears at low temperature [ 171 ].…”

“…Inset: bandgap at various temperatures (adopted from [ 113 ], with permission from the American Chemical Society, 2017). ( b ) Temperature-dependent absorption of perovskite solar cells (adapted from [ 39 ], with permission from Wiley-VCH, 2019). ( c ) Temperature-dependent optical bandgap of perovskite solar cells (adapted from [ 39 ], with permission from Wiley-VCH, 2019).…”

“…( b ) Cooling-enhanced PCE and FF of perovskite solar cells (adapted from [ 164 ], with permission from Wiley-VCH, 2019). ( c ) Phase transition (adapted from [ 39 ], with permission from Wiley-VCH, 2019). ( d ) Composition and structure (adapted from [ 165 ], with permission from Wiley-VCH, 2018).…”

“…Some intrinsic characteristics of carriers are reported to show huge enhancement from cooling, including mobility [ 36 ], diffusion length [ 37 ] and corresponding densities [ 38 ]. For specific materials, structure transition [ 39 ] has been observed in a low-temperature range, providing more potential for cooling regulation. When the above phenomena integrated with devices, the cooling-enhanced properties in devices can be classified into absorption [ 40 ], carrier diffusion and recombination [ 41 , 42 ], resistance [ 43 ], photoconductivity [ 44 ], permittivity [ 45 ], interfaces and defects [ 46 ] and can improve the overall performance of both photodetectors and solar cells.…”