Triggering the Passivation Effect of Potassium Doping in Mixed‐Cation Mixed‐Halide Perovskite by Light Illumination

Abstract

To improve the thermal stability and broaden the absorption spectrum range of PSCs, mixed-cation mixed-halide perovskites(FA x MA 1-x PbI y Br 3-y ) with bandgap tunability are widely used. [7,8] The recent trend of cation doping has seen the increase of A-site diversity away from purely organic cations such as methylammonium (MA + ) and formamidinium (FA + ), to complex cations composed of major organic cations doped with alkali cations such as cesium (Cs + ), rubidium (Rb + ), and potassium (K + ). [9][10][11] Triple-or quadruple-cation perovskites with a few percent of Cs + , Rb + , or K + doping have already been successfully achieved, demonstrating improved performance stability and suppressed J-V hysteresis in PSC devices. [12,13] Cs + doping into FA/MA-based perovskites can improve the structural stability by suppressing the formation of the orthorhombic δ-phase (non-photoactive "yellow phase"), achieving high-efficiency PSCs with stabilized PCE of 21.1%. [9] Further doping of triple cation CsFAMA perovskite by oxidation-stable rubidium cation (Rb + ) leads to low-voltage-loss PSCs with efficiencies of up to 21.6% and long-term device stability at elevated temperature. [10] More recently, the smaller alkali cation K + was introduced into CsFAMA perovskite to tune the film morphology and optoelectronic property. [13,14] The incorporation of K + effectively increases the grain size and reduces the interfacial defect density in the perovskite layer, leading to hysteresis-free, stable, and high PCE (20.56%) quadruple-cation PSCs. [13] Although great improvements in photovoltaic performance have been achieved by alkali cation doping, the precise role of these dopants in enhancing device stability is still unclear. According to Goldsmith's theory, only Cs + can form stable perovskite structures when occupying the A-site of the crystal lattice, with a tolerance factor ( =where R is the ionic radius) falling in the eligible range between 0.8 and 1. [15] Other alkali cations (Rb + , K + ) are too small for appropriate replacement of organic cations in the A-site and are believed to be located in the interstitial sites of the perovskite lattice. [16][17][18] Perovskite lattice expansion and corresponding bandgap variation upon incorporation of small radius alkali cations (Rb + , K + and Na + ) were observed by X-ray diffraction and energy-dispersive X-ray spectroscopy. [11] Theoretical work based on density functional theory (DFT) calculations by Cao et al.Potassium (K + ) doping has been recently discovered as an effective route to suppress hysteresis and improve the performance stability of perovskite solar cells. However, the mechanism of these K + doping effects is still under debate, and rationalization of the improved performance in these perovskites is needed. Herein, the photoluminescence (PL) properties and device performance of mixed-cation mixed-halide perovskite are dynamically monitored with and without K + doping under bias light illumination via a confocal fluorescence microscope, together with ultraf...

Coexistence of light-induced photoluminescence enhancement and quenching in CH3NH3PbBr3 perovskite films

“…The short lifetime can be assigned to excitonic recombination considering the relatively large exciton binding energy of CH 3 NH 3 PbBr 3 , while the long lifetime represents the trapped-assisted recombination. 37 As shown in Fig. 3b, aer 10 min illumination, the weight ratio of trap-assisted recombination decreases, which suggests a decrease of trap density and is consistent with the PLIE in the initial stage shown in Fig.…”

Revealing the Dynamics of Hybrid Metal Halide Perovskite Formation via Multimodal In Situ Probes

“…Yet, the highest PL intensity still appears in the same time frame (≈800 s). Currently, the influence of light during synthesis is not fully understood in the perovskite community; we believe that in situ PL could be a promising platform to further examine the light effects on perovskite formation.…”

Beneficial effects of potassium iodide incorporation on grain boundaries and interfaces of perovskite solar cells

“…The charge trapping induced by the defect states at the GBs will then be eliminated. 24 In Fig. 4e, we plotted the CPD distribution of GBs corresponding to the black and red squares in Fig.…”