陳江照&臧志剛&許宗祥JEC：高效穩定鈣鈦礦太陽能電池中由多種化學鍵協同誘導的自下而上的整體載流子管理策略

有機無機金屬鹵化物鈣鈦礦太陽能電池（PSC）因其低成本和高功率轉換效率（PCE）而受到廣泛關注，顯示出潛在的商業價值。電子傳輸層（ETL）對實現穩定高效的正置器件起著至關重要的作用。TiO₂和SnO₂ ETL已廣泛應用于常規PSC中。SnO₂納米粒子的團聚會顯著降低器件在批次間的重現性，這可能會阻礙其商業應用。此外，SnO₂ ETL還存在氧空位（O_V）缺陷，表現出較差的載流子提取和傳輸能力。除ETL外，高效SnO₂基PSC的實現還高度依賴于鈣鈦礦薄膜的質量。除了ETL和鈣鈦礦層外，為了最小化界面和體相非輻射復合損失，調節界面是非常重要的。鈣鈦礦和SnO₂薄膜的埋底界面有許多缺陷，這些缺陷會阻礙載流子的提取，導致界面電荷積累和界面非輻射復合。然而，僅通過在鈣鈦礦薄膜中加入添加劑分子或在埋底界面處引入界面改性劑，很難同時解決上述問題和實現整體載流子管理。

鑒于此，重慶大學陳江照研究員、臧志剛教授及南方科技大學許宗祥副教授等人提出了一種由多種化學鍵協同誘導的自下而上的整體載流子管理策略，以最大限度地減少高效鈣鈦礦太陽能器電池的體相和界面能量損失。該策略是通過將含有豐富官能團（-CF₃、–NH₂–C=NH₂⁺和Cl^-）的4-三氟甲基苯甲脒鹽酸鹽（TBHCl）直接加入到SnO₂膠體溶液中來實現的，并且還將僅含有-CF₃的三氟甲苯（BTF）和僅含有甲脒陽離子和Cl^-陰離子的苯甲脒鹽酸鹽（BHCl）用作對照分子，以揭示目標分子中每個官能團的功能。結果表明，F和Cl^-均可以通過與Sn⁴⁺配位鈍化SnO₂中的氧空位和/或未配位Sn^4＋缺陷，但前者比后者更有效。F可以通過與FA⁺形成氫鍵來抑制陽離子遷移和調節結晶，并且可以通過與Pb²⁺配位來鈍化鉛缺陷。–NH₂–C=NH₂⁺和Cl^-可分別通過與鈣鈦礦形成離子鍵和/或靜電相互作用來鈍化陽離子和鹵素陰離子空位缺陷。總之，目標分子中的各個官能團各司其職，展現了良好的協同作用，從而實現了多鍵誘導的自下而上的整體載流子管理。通過TBHCl改性，抑制了SnO₂納米粒子的團聚、鈍化了ETL中的氧空位缺陷和鈣鈦礦薄膜中的缺陷以及釋放了鈣鈦礦膜中的拉伸應變，從而將PCE從21.28%提高到23.40%。結合PEAI鈍化，效率進一步提高到23.63%。TBHCl改性器件具有優異的熱和濕度穩定性。該工作為開發由多種化學鍵協同誘導的自下而上的整體載流子管理策略來提升器件的效率和穩定性提供了借鑒，為鈣鈦礦太陽能電池的商業化應用奠定了堅實的基礎。

Fig. 1. (a) Schematic illustration of multiple-chemical-bond-induced bottom-up holistic modification based on TBHCl. (b) Sn 3d and (c) O 1s XPS spectra of the SnO₂ films without or with modifiers. ¹⁹F NMR spectra of the SnO₂ solutions without and with (d) BTF and (e) TBHCl. ¹H NMR spectra of the SnO₂ solutions without and with (f) BTF and (g) TBHCl. (h) FTIR spectra of SnO₂, SnO₂-TBHCl film, and pure TBHCl in the range of 1000-1200 cm^-1. (i) Pb 4f XPS spectra of the perovskite films prepared on pristine SnO₂ and modified SnO₂ with BTF, BHCl and TBHCl. (j) ¹⁹F NMR spectra of TBHCl, TBHCl+PbI₂ and TBHCl+FAI. (k) ¹H NMR spectra of TBHCl, TBHCl+PbI₂, TBHCl+FAI, and FAI.

Fig. 2. (a) Electrostatic potential map of BTF, BHCl and TBHCl molecules. (b) Binding energies (E_b) between the O_V defects in SnO₂, iodine vacancy and FA vacancy defects in FAPbI₃ in contact with BTF, BHCl and TBHCl molecules. Optimized structures of SnO₂ surface containing O_V defects (c) without and with (d) BTF, (e) BHCl, and (f) TBHCl. Optimized structures of FAPbI₃ surface containing iodine vacancy defects (g) without and with (h) BTF, (i) BHCl, and (j) TBHCl. Optimized structures of FAPbI₃ surface containing FA vacancy defects (k) without and with (l) BTF, (m) BHCl, and (n) TBHCl.

Fig. 3. DLS spectra of fresh and aged (a) SnO₂, (b) SnO₂-BTF, (c) SnO₂-BHCl and (d) SnO₂-TBHCl. (e) Current-voltage curves for the devices with the structure of ITO/SnO₂ without or with modifiers/Ag. The ITO and PCBM stand for the indium-tin oxide-coated glass substrate and phenyl-C61-butyric acid methyl ester layer, respectively. (f) Electron mobility of the electron-only devices with the structure of ITO/PCBM/SnO₂ without and with BTF, BHCl and TBHCl/PCBM/Ag. (g) XRD for the control, BTF-, BHCl- and the TBHCl-modified perovskite films. GIXRD patterns with different ω values (0.5~1.5) for (h) control, (i) BTF-, (j) BHCl-, and (k) TBHCl-modified perovskite films. (l) The d-spacing value of the (211) plane as a function of grazing incidence angle for the control, BTF-, BHCl- and the TBHCl-modified perovskite films.

Fig. 4. Top-view SEM images of (a) control, (b) BTF-, (c) BHCl-, and (d) TBHCl-modified perovskite films. The scale bar is 1 μm. PL mapping images of (e) glass/perovskite, (f) glass/BTF/perovskite, (g) glass/BHCl/perovskite and (h) glass/TBHCl/perovskite films. (i-l) Current-voltage curves for the electron-only devices which was composed of ITO/SnO₂ without or with modifiers /perovskite/PCBM/BCP/Ag.

Fig. 5. (a) TRPL spectra of the perovskite films based on the pristine SnO₂ and SnO₂ modified with BTF, BHCl, and TBHCl. Transient reflection kinetics for the perovskite films deposited on (b) SnO₂, (c) SnO₂-BTF, (d) SnO₂-BHCl and (e) SnO₂-TBHCl ETLs. (f) TPC and (g) TPV decay curves of the PSCs based on SnO₂, BTF-, BHCl- and TBHCl-modified ETLs. (h) EIS measurement of the devices based on control, BTF, BHCl, and TBHCl ETLs. The inset shows equivalent circuit of the device. (i) The light-intensity dependence of V_OC curves for the control and modified devices.

Fig. 6. (a) J_SC, (b) V_OC, (c) FF and (d) PCE of the control and PSCs based on the optimal concentration of BTF, BHCl and TBHCl. J-V characteristics of the best-performing PSCs based on (e) control, (f) BTF, (g) BHCl and (h) TBHCl. (i) J-V curves of the champion TBHCl modified device with PEAI post-treatment. (j) Steady state output performance of the champion PSCs without and with BTF, BHCl and TBHCl modification. (k) Thermal stability of the unencapsulated PSCs without and with modifiers at 60 ℃ in a N₂-filled glove box. (l) Humidity stability test of unencapsulated PSCs without and with modifiers aged under a relative humidity of 15-25% at room temperature in the dark.

Baibai Liu,¹ Ru Li,¹ Qixin Zhuang, Xuemeng Yu, Shaokuan Gong, Dongmei He, Qian Zhou, Hua Yang, Xihan Chen, Shirong Lu, Zong-Xiang Xu,* Zhigang Zang* and Jiangzhao Chen*. Bottom-up holistic carrier management strategy induced synergistically by multiple chemical bonds to minimize energy losses for efficient and stable perovskite solar cells. Journal of Energy Chemistry 2022, https://doi.org/10.1016/j.jechem.2022.09.037.