Healing the Buried Cavities and Defects in Quasi-2D Perovskite Films by Self-Generated Methylamine Gas

Abstract

Perovskites with grain size comparable to film thickness are intensively pursued for high-efficiency solar cells. Geometrically, large grains with high crystallinity tend to form polyhedral shapes that have difficulty forming compact and smooth films. When quasi-two-dimensional RP perovskite films adopt a downward growth mode, defective contacts tend to form at their bottom interfaces with many nanocavities. This is attributed to the angular growing fronts of RP perovskite grains adopting [111] (or/and [101]) growth directions. Self-generated methylamine gas, by a replacement reaction in solution, is introduced to in situ heal these irregular nanocavities that are deeply buried in perovskite films during crystallization processes. The amount of self-generated methylamine gas should be adequately controlled to avoid the homogeneous nucleation of perovskites from a liquid perovskite-amine intermediate phase, which is a key to avoid ruining the grain size and film composition. This in situ healing strategy offers significantly enhanced charge collection efficiency and device working stability.

Inhibition of buried cavities and defects in metal halide perovskite photodetectors via a two-step spin-coating method

“…21,[27][28][29][30][31][32] However, the volume expansion caused by the transformation of the edge-sharing octahedral framework of PbI 2 into the corner-sharing octahedral framework of MAPbI 3 limits the pathway for the diffusion of MAI molecules deeper into the PbI 2 film, resulting in the incomplete conversion of PbI 2 to MAPbI 3 and buried nanocavities at the bottom interface of perovskite. 20,30,[33][34][35] To address the above-mentioned issues, many efforts have been devoted to ameliorating the crystallization and morphology of MAPbI 3 polycrystalline films, which can be roughly be summed up as constructing mesoporous PbI 2 films and ligand modulation. Firstly, a mesoporous PbI 2 framework can be constructed by using PbI 2 precursors mixed with a fraction of additives (CaI 2 , 36 TBP, 37 and MAI 30 ) after spin-coating and annealing, which facilitates their complete conversion accompanied with a larger grain.…”

“…Recent studies suggest that non-radiative losses correlated with buried nanocavities, crystalline defects and complex phases hinder the device performance at the interfaces with the bottom contact layer. 20,31,[33][34][35]37,[39][40][41][42] Consequently, it is highly desirable to minimize non-radiative recombination and eliminate buried nanocavities for efficient perovskite photodetectors.…”

Ordered Element Distributed C3N Quantum Dots Manipulated Crystallization Kinetics for 2D CsPbI3 Solar Cells with Ultra‐High Performance

“…[28] When the 2D perovskite grows in a downward growth mode, the defective contact would happen at the bottom interface and form a serrated bottom surface with intergranular cavities. [29,30] Moreover, the specific crystal plane growth of perovskite and surface trap state of TiO 2 further make it more difficult to control the morphology of the perovskite film. [31][32][33] 2) Poor phase-arrangement ability.…”

A cascade bilayer electron transport layer toward efficient and stable Ruddlesden‐Popper perovskite solar cells

“…3‐Dimensional (3D) organolead‐trihalide perovskites (APbX 3 , A = ammonium cation, X = I, Br, or Cl) have emerged as a promising photoactive material due to its fascinating optoelectronic properties such as high absorptivity, shallow defect levels, and long carrier lifetimes, and the power conversion efficiencies (PCEs) reported for perovskite solar cells (PSCs) have rapidly enhanced to >25% in a single‐junction device, which is competitive with silicon or inorganic counterparts 1‐12 . Meanwhile, Ruddlesden‐Popper perovskites (RPPs) are another interesting class of perovskite absorber described by a formula of A′ 2 A n −1 B n X 3 n +1, where A′ and A is a large organic cation (eg, n ‐butylammonium) and a monovalent cation (eg, methylammonium), respectively 13‐19 . Because the large organic cations isolate the perovskite layers efficient charge extraction and transport in the perovskite absorber layer is limited, so the RPP‐based PSCs usually exhibited relatively inferior short‐circuit current density ( J SC ), fill factor (FF) as compared to 3D APbX 3 ‐type PSCs.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12] Meanwhile, Ruddlesden-Popper perovskites (RPPs) are another interesting class of perovskite absorber described by a formula of A 0 2 A nÀ1 B n X 3n+1, where A 0 and A is a large organic cation (eg, n-butylammonium) and a monovalent cation (eg, methylammonium), respectively. [13][14][15][16][17][18][19] Because the large organic cations isolate the perovskite layers efficient charge extraction and transport in the perovskite absorber layer is limited, so the RPP-based PSCs usually exhibited relatively inferior short-circuit current density (J SC ), fill factor (FF) as compared to 3D APbX 3 -type PSCs. To resolve this issue, early works have studied the manipulation of the crystal structure of RPP by varying the alkylammonium or monovalent cations and its impact on the photovoltaic properties of the device.…”