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Organic cations such as methylamine or formamidine in organic-inorganic hybrid perovskites readily react with oxygen or water at high temperatures, leading the perovskite structure to decompose into organic gases and lead iodide finally. In order to solve the instability problem of organic cations, researchers have studied the heat-resistant all inorganic CsPbX3 (X is Cl, Br, I or mixed halide) perovskites. Mixed halide perovskite CsPbI2Br, serving as a top cell in semi-transparent solar cells and tandem cells because of its excellent thermal stability and suitable bandgap (1.90 eV), has attracted much attention. Although high-performance CsPbI2Br solar cells can be prepared in a glove box, this preparation method not only increases its cost but also has complex manufacturing process, unsuitable for low-cost commercial manufacturing. However, CsPbI2Br thin films prepared in ambient air are susceptible to humidity, resulting in low coverage, poor crystallization quality, numerous pinholes, and easy transformation into non perovskite phases. To overcome the troubles of pervoksite fabrication in ambient air, a feasible way is to reduce the moisture around the films as much as possible according to dynamic hot-air assisted strategy. However, the hot air accelerates the evaporation rate of solvent, resulting in the decrease of grain size. In order to improve the crystal growth and long-term stability in dynamic hot-air assisted strategy, in this work, we present a dynamic hot-air assisted recrystallization (DHR) strategy to prepare high-quality CsPbI2Br thin films in ambient air (i.e. the CsPbI2Br thin films prepared via dynamic hot-air strategy are recrystallized by using a green solvent (methylamine acetate) with high viscosity coefficient). Under ambient air with high humidity (RH＞60%), the CsPbI2Br thin film with high coverage, (100) preferred orientation, large average grain size, and stable structure is prepared via DHR strategy. The dynamic hot-air process can effectively reduce the moisture around the film and increase the nucleation sites in the precursor solution, thereby improving the coverage of the film. However, this process inevitably results in the significant decrease of grain size (Rave= 0.32 μm) (i.e. more grain boundaries), exacerbating non-radiative recombination of carriers associated with trap states at these boundaries. The high coverage increases the grain-to-grain contact area, facilitating complete recrystallization. Thus, the recrystallization process can significantly increase the grain size (Rave = 2.63 μm) and obtain a (100) preferred orientation (I(110)/I(200) = 0.006), resulting in high photoluminescence intensity and long fluorescence lifetime (118 ns). The unencapsulated CsPbI2Br perovskite solar cell (PSC) optimized via DHR strategy with low hysterescence factor (2.34%) and high repeatability exhibits a high power conversion efficiency (PCE = 17.55%), which is higher than those of most CsPbI2Br PSCs prepared in ambient air and gloveboxes previously reported. Moreover, the unencapsulated CsPbI2Br PSC possesses an excellent storage stability under ambient air with high humidity (RH > 60%), remaining 96% of the original PCE after aging 40 days. This provides a promising approach for achieving high-performance and long-term stable CsPbI2Br films under ambient air with high humidity, which is expected to promote the commercialization process of perovskite/silicon tandem cells and semi-transparent devices.
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Keywords:
- CsPbI2Br /
- dynamic hot-air assisted recrystallization /
- ambient air /
- photoelectric performance
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图 1 对照组和优化组薄膜的 (a) OM表面形貌图、(b) AFM表面形貌图、(c)晶粒尺寸统计图、(d) XRD图谱和(e)示意图
Figure 1. The (a) OM images, (b) AFM images, (c) grain size statistics, (d) XRD patterns, and (e) schematic of the control group and optimized group thin films.
图 2 CsPbI2Br单胞的 (a)晶体结构和(b)能带结构; 对照组和优化组薄膜的(c)紫外可见吸收光谱及PL光谱(实线表示玻璃基底上PVSK的PL光谱; 方块表示SnO2上PVSK的PL光谱)
Figure 2. (a) Crystal structure and (b) band structure of CsPbI2Br unit cell; (c) UV-vis absorption spectra and PL spectra of the control group and optimized group thin films. (the solid line represents the PL spectra of PVSK on glass; the square dots represent the PL spectra of PVSK on SnO2).
图 3 对照组和优化组薄膜的 (a)吸收系数的对数形式与光子能量的曲线图, (b)透射光谱, (c)TRPL光谱, 以及(d)—(g)老化图像及其紫外可见吸收光谱
Figure 3. The (a) ln(α) versus energy, (b) transmission spectra, (c) TRPL spectra, and (d)–(g) photos and UV-vis absorption spectra with aging time of the control group and optimized group thin films.
图 4 对照组和优化组钙钛矿太阳能电池的 (a)光电流密度-电压曲线, (b)光电流密度-电压正反扫曲线, (c)外量子效率, (d)转换效率统计分布图, (e)短路电流统计分布图, (f)开路电压统计分布图, (g)填充因子统计分布图, (h)开路电压随光照强度变化, (i)电流-电压曲线, (j)储存稳定性
Figure 4. The (a) J-V curves, (b) hysteresis curves, (c) EQE spectra, (d) PCE statistics, (e) JSC statistics, (f) VOC statistics, (g) FF statistics, (h) light intensity-dependent VOC variation, (i) current-voltage curves, and (j) storage stability of the control group and optimized group perovskite solar cells.
表 1 对照组与优化组CsPbI2Br薄膜TRPL光谱的拟合参数
Table 1. Fitting parameters of TRPL spectra for the control group and optimized group CsPbI2Br thin films.
Sample A1 τ1 /ns A2 τ2 /ns τave/ns Control 0.92 6.45 0.08 118 75 REC 0.91 7.35 0.09 160 112 DHA 0.71 2.77 0.29 105 99 DHR 0.69 9.36 0.31 135 118 
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表 2 采用动态热风辅助再结晶策略的CsPbI2Br太阳能电池与其他CsPbI2Br太阳能电池的性能比较
Table 2. Performance comparison of CsPbI2Br solar cells via dynamic hot-air assisted recrystallization strategy with other reports.
年份 制备环境 策略 效率/% 稳定性 文献 2022 N2 Doping 16.20 88.6%, 42 day
(air, 30% RH)[35] 2023 N2 Interface engineering 17.33 88.7%, 42 day
(air, 10% RH)[36] 2023 N2 Doping 17.70 97%, 42 day
(air, 10% RH)[37] 2019 air, 25~35% RH DHA 14.85 90%, 17 day
(air, 85 ℃)[17] 2020 air, 30% RH Precursor engineering 16.14 93%, 35 day
(air, 30% RH)[18] 2021 air, 35% RH DHA+Doping 17.46 80%, 17 day
(air, 30% RH)[38] 2023 air, — DHA+Doping 16.74 90%, 17 day
(air, 25% RH)[39] 2023 air, 20% RH DHA+Doping 17.39 84%, 9 day
(N2, 85 ℃)[19] 2023 air, — Doping 17.38 90%, 42 day
(air, 25% RH)[40] 2023 air, — DHA+Doping 17.40 87.25%, 30 day (air, 14% RH) [41] 2024 air, ＞60% RH DHR 17.55 96%, 40 day
(air, ＞60% RH)This work
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