Robust Stability of Efficient Lead-Free Formamidinium Tin Iodide Perovskite Solar Cells Realized by Structural Regulation

Abstract

The instability issue of Pb-free Sn-based perovskite is one of the biggest challenges for its application in optoelectronic devices. Herein, a structural regulation strategy is demonstrated to regulate the geometric symmetry of formamidiniumtin iodide (FASnI 3) perovskite. Experimental and theoretical works show that the introduction of cesium cation (Cs⁺) could improve the geometric symmetry, suppress the oxidation of Sn²⁺, and enhance the thermodynamical structural stability of FASnI 3. As a result, the inverted planar Cs-doped FASnI 3-based perovskite solar cell (PSC) is shown to maintain 90% of its initial power-conversion efficiency (PCE) after 2000 h stored in N 2 , which is the best durability to date for 3D Sn-based PSCs. Most importantly, the air, thermal, and illumination stabilities of the PSCs are all improved after Cs doping. The PCE of the Cs-doped PSC shows a 63% increase compared to that of the control device (from 3.74% to 6.08%) due to the improved quality of the Cs-doped FASnI 3 film.

Strategies for Improving the Stability of Tin‐Based Perovskite (ASnX3) Solar Cells

“…[ 99 ] In 2018, Gao et al introduced Cs + into the FASnI 3 lattice to shrink the lattice with a tolerance factor t close to 1, as shown in Figure a,b. [ 100 ] As a result, the optimum PCE was 6.08%, which was 63% higher than that of the control device (3.74%). Oxidation of Sn 2+ was inhibited and good stability was obtained.…”

“…Reproduce with permission. [ 100 ] Copyright 2018, American Chemical Society Publications. c) Schematic diagram of the cation exchange process.…”

Lead‐Free Tin‐Based Perovskite Solar Cells: Strategies Toward High Performance

“…Similar to Pb analogs, smaller radius Cs + doping is able to regulate structural symmetry, optoelectronic properties, and stability . Based on experimental and theoretical results, Gao et al claimed that the introduction of Cs + can contract the crystal lattice with a tolerance factor t closer to 1 and thus improve the stability of FASnI 3 against the oxidation of Sn 2+ as well as other extrinsic factors such as heat and illumination (Figure d) . The champion device with 8% Cs + doping displayed a PCE of 6.08%, a 63% increase compared with one of the control devices (3.73%), and maintained 90% of its initial PCE after 2000 hours' storage in N 2 (Figure e,f).…”

“…f) Stability tests of PSC devices with or without Cs doping stored in N 2 . Reproduced with permission . Copyright 2018, American Chemical Society. g) Potential energy diagrams of GA x FA (0.98‐x) SnI 3 –1% EDAI 2 (E1Gx) films with GAI (x = 0–0.3).…”

Database-driven high-throughput study of coating materials for hybrid perovskites

“…With increasing exposure to any of these destabilizing factors, the structure of the hybrid perovskite degrades and the PCE reduces concomitantly after several days or even hours [15,16]. Among the solutions that have been proposed to solve this stability and longevity problem are protective coating [17][18][19], the use of two-dimensional perovskites [20][21][22][23][24][25], and doping with small ions [14,[26][27][28][29][30]. Protective coating is particularly promising, as it can passivate the surface dangling bonds of the perovskite photoabsorber [31] and insulate the perovskite from heat and small molecules from the environment [17][18][19].…”