Photodoping through local charge carrier accumulation in alloyed hybrid perovskites for highly efficient luminescence

Abstract

Metal-halide perovskites have emerged as exceptional semiconductors for optoelectronic applications. Substitution of the monovalent cations has advanced luminescence yields and device efficiencies. Here, we control the cation alloying to enhance optoelectronic performance through alteration of the charge carrier dynamics in mixed-halide perovskites. In contrast to singlehalide perovskites, we find high luminescence yields for photo-excited carrier densities far below solar illumination conditions. Using time-resolved spectroscopy we show that the charge-carrier recombination regime changes from second to first order within the first tens of nanoseconds after excitation. Supported by microscale-mapping of the optical bandgap, electrically-gated transport measurements and first-principles calculations, we demonstrate that spatially-varying energetic disorder in the electronic states causes local charge accumulation, creating p-and n-type photodoped regions, which unearths a strategy for efficient light emission at low charge-injection in solar cells and LEDs. Metal-halide perovskites exhibit outstanding optoelectronic properties, such as low Urbach energies, high carrier mobilities and diffusion lengths, as well as very high photoluminescence quantum efficiencies (PLQEs), 1 which are essential to achieve performance limits in solar cells and light-emitting diodes (LEDs). 2-5 This culminated in reported photovoltaic performances 6,7 exceeding 25 % upon incorporation of a series of monovalent cation mixtures (formamidinium, Cs) and passivating additives (Rb, K) to the methylammonium mixed-halide perovskite prototype MAPb(Br0.17I0.83)3 8,9 , as well as bright LEDs 10-15. Here, we show that local bandgap variations in mixed-halide thin films yield photo-doped regions for efficient photoluminescence, favourable for optoelectronic applications.

Photobrightening in Lead Halide Perovskites: Observations, Mechanisms, and Future Potential

“…This variation leads to shallow states and subsequently local accumulation of one type of photoexcited carrier through a photodoping effect. [66] Interestingly, independent of the Adv. Energy Mater.…”

Phase Segregation and Photothermal Remixing of Mixed-Halide Lead Perovskites

“…As such, the carriers can be intrinsically split among the domains which either extend the lifetime of the carriers or hindered them from being collected depending on the locations of the domains relative to the electrodes. [14][15][16] The phase segregation has been suspected to be initialized by either single-exciton 28 or the accumulation of one kind of carrier on the surface of a grain or a nanocrystal. This internal electric field breaks Pb-halide bonds and moves halides around, 29,30 which often generates neutral X2 species.…”

Carrier Dynamics and Evaluation of Lasing Actions in Halide Perovskites

“…In Equation 1, the electron density is assumed to be equal to the hole density (n = n e = n h ), which is usually realized through optical excitation or balanced electrical injection. However, exceptions exist when we consider the nonnegligible intrinsic or doping concentration terms [77]. Moreover, electrons and holes can be unbalanced when the majority of electrons or holes are trapped due to trap filling processes.…”