Manipulating the Formation of 2D/3D Heterostructure in Stable High‐Performance Printable CsPbI₃Perovskite Solar Cells

Abstract

Manipulating the formation process of the 2D/3D perovskite heterostructure, including its nucleation/growth dynamics and phase transition pathway, plays a critical role in controlling the charge transport between 2D and 3D crystals, and consequently, the scalable fabrication of efficient and stable perovskite solar cells. Herein, the structural evolution and phase transition pathways of the ligand‐dependent 2D perovskite atop the 3D surface are revealed using time‐resolved X‐ray scattering. The results show that the ligand size and shape have a critical influence on the final 2D structure. In particular, ligands with smaller sizes and more reactive sites tend to form the n = 1 phase. Increasing the ligand size and decreasing the reactive sites promote the transformation from 3D to n = 3 and n < 3 phases. These findings are useful for the rational design of the phase distribution in 2D perovskites to balance the charge transport and stability of the perovskite films. Finally, solar cells based on ambient‐printed CsPbI3 with n‐butylammonium iodide treatment achieve an improved efficiency of 20.33%, which is the highest reported value for printed inorganic perovskite solar cells.

Two‐Second‐Annealed 2D/3D Perovskite Films with Graded Energy Funnels and Toughened Heterointerfaces for Efficient and Durable Solar Cells

“…The concomitant decay and rise components with similar timescales for different perovskite phases suggested cascade energy/charge transfer from low-n 2D perovskite phase to high-n quasi-2D perovskite phase and finally to 3D perovskite phase (n = ∞), which can be attributed to the spontaneous bottom-up formation of 2D/3D perovskite energy funnels that were aligned in the abovementioned ascending order of n values across the perovskite film. [31][32][33][34][35][36][37] Moreover, after ca. 20 ps, the n = 4 perovskite phase showcased an enhanced signal, which can be possibly ascribed to the consecutive hole transfer from 3D perovskite to 2D phases.…”

“…20 ps, the n = 4 perovskite phase showcased an enhanced signal, which can be possibly ascribed to the consecutive hole transfer from 3D perovskite to 2D phases. [34] In general, the electron transfer from 2D perovskites to 3D perovskites is more efficient than the backward hole transfer from 3D components to 2D phases, which might account for the slightly deferred threshold of hole transfer following the occurrence…”

Surface Engineering toward High-Performance CsPbI3 Perovskite Solar Cells

“…To gain insight into the effects, Du et al selected three cations with different sizes to treat the CsPbI 3 film, including guanidinium iodide (GAI), n-butylammonium iodide (BAI), and phenylbutylammonium iodide (PBAI) (Figure 6g). 98 As indicated, since the GA + ions have the smallest effective radius and three "electron depletion regions", they could be introduced into the 3D CsPbI 3 lattice by interacting with a [PbI 6 ] 4− octahedron and hence form an n = 1 2D perovskite capping layer to passivate surface defects, while the BA + and PBA + were likely to form the 2D perovskite with larger n. Particularly, the BA + would form 2D perovskite with reduced dimensionalities (n = 1 layered BA 2 PbI 4 2D phase and n = 2 BA 2 CsPbI 7 2D phase) on the surface of 3D CsPbI 3 perovskite. The 2D quantum wells with graded band gap optimized the energy level alignment in CsPbI 3 -BAI PSCs, thereby facilitating the charge exaction and transport at the perovskite/HTL interface (Figure 6h).…”

“…As mentioned above, the structure and properties of foreign cations greatly affected the formation of LD perovskite on CsPbI 3 perovskite. To gain insight into the effects, Du et al selected three cations with different sizes to treat the CsPbI 3 film, including guanidinium iodide (GAI), n -butylammonium iodide (BAI), and phenylbutylammonium iodide (PBAI) (Figure g) . As indicated, since the GA + ions have the smallest effective radius and three “electron depletion regions”, they could be introduced into the 3D CsPbI 3 lattice by interacting with a [PbI 6 ] 4– octahedron and hence form an n = 1 2D perovskite capping layer to passivate surface defects, while the BA + and PBA + were likely to form the 2D perovskite with larger n .…”

Post‐Treatment of Metal Halide Perovskites: From Morphology Control, Defect Passivation to Band Alignment and Construction of Heterostructures

“…[21,[68][69][70][71][72] The self-assembled reduced-dimensional perovskites (RDPs) or low-dimensional perovskites (LDPs) are found to not only passivate the surface defects but also enable a 3D/2D heterostructure with favorable band alignment. [73][74][75][76] In the stateof-the-art, the most efficient PSCs are using such 3D/2D perovskite heterostructure as the light-harvesting layer in the cells. By selecting proper bulky cations and developing suitable processing technique, the n values and optoelectronic properties of the RDPs can be tuned.…”