In Situ Observation of Vapor-Assisted 2D–3D Heterostructure Formation for Stable and Efficient Perovskite Solar Cells

Abstract

The heterogeneous stacking of a thin two-dimensional (2D) perovskite layer over the three-dimensional (3D) perovskite film creates a sophisticated architecture for perovskite solar cells (PSCs). It combines the remarkable thermal and environmental stabilities of 2D perovskites with the superior optoelectronic properties of 3D materials which resolves the chronic stability issue with no compromise on efficiency. Herein, we propose the vapor-assisted growth strategy to fabricate high-quality 2D/3D heterostructured perovskite films by introducing long-chain organoamine gases in which the 2D layers have a uniform and tunable thickness. The 3D to 2D transformation of the widely adopted MAPbI3 (MA = methylammonium) film is initiated by the butylamine vapor and monitored through the in situ grazing-incidence X-ray diffraction technique. A variety of 2D species are observed and rationalized by the different collapsing and reconstruction models of the Pb–I octahedra. The PSC devices based on the optimized 2D/3D heterostructures show significant improvements in photovoltaic performances, owing to better energy level alignments, longer carrier lifetimes, and less defects as compared to their 3D analogues. In addition, both the butylamine vapor-treated perovskite films and the derived PSC devices demonstrate exceptional long-term stabilities.

3D/2D Bilayerd Perovskite Solar Cells with an Enhanced Stability and Performance

“…To this end, the solvent-free method has been tested by using vapors to form a thin 2D layer on the surface of the 3D film in various conditions. In the vapor deposition or vapor-assisted method, the 3D/2D bilayered structure is developed by the permeation of organoamine gases for 2D into the 3D film from the surface [ 45 ]. The 3D perovskite film is exposed to the vapors being generated from the heated organoamine liquid or organic salt [ 46 ].…”

“…The 3D perovskite film is exposed to the vapors being generated from the heated organoamine liquid or organic salt [ 46 ]. Chen et al formed a 2D perovskite capping layer by exposing the 3D perovskite film, prepared by the conventional solution method, to butylamine vapor in a sealed box containing an open bottle filled with butylamine liquid, leading to a surface conversion from 3D to 2D perovskite [ 45 ]. Meanwhile, Xu et al built an entire 3D/2D perovskite structure by vapor deposition [ 46 ].…”

“…The prepared 3D bulk film, MAPbI 3 , was sequentially exposed to BAI vapor in the vacuum oven at 120 °C, with the exposure time being varied from 5 to 60 min to form the 2D layer on the top. It was found that the quality and conversion degree of the 2D layer are fully controllable by modulating the vapor-treatment time in solvent-free methods [ 45 , 46 ]. Similarly, 3D and 2D perovskite layers can be independently deposited by using a thermal vacuum evaporator.…”

“…Sometimes, a small morphology change is observed after the growth of a 2D layer, where an extremely thin 2D layer is piled up without causing any major change in the surface morphology [ 34 , 45 ].…”

“…Figure 10 shows the normalized PCE of devices at 85 °C [ 45 ]. The device based on a 3D/2D bilayered structure apparently demonstrated an improved thermal stability compared to the device with a 3D film.…”