有机无机金属卤化物钙钛矿太阳能电池（PSC）因其低成本和高功率转换效率（PCE）而受到广泛关注，显示出潜在的商业价值。电子传输层（ETL）对实现稳定高效的正置器件起着至关重要的作用。TiO₂和SnO₂ ETL已广泛应用于常规PSC中。SnO₂纳米粒子的团聚会显著降低器件在批次间的重现性，这可能会阻碍其商业应用。此外，SnO₂ ETL还存在氧空位（O_V）缺陷，表现出较差的载流子提取和传输能力。除ETL外，高效SnO₂基PSC的实现还高度依赖于钙钛矿薄膜的质量。除了ETL和钙钛矿层外，为了最小化界面和体相非辐射复合损失，调节界面是非常重要的。钙钛矿和SnO₂薄膜的埋底界面有许多缺陷，这些缺陷会阻碍载流子的提取，导致界面电荷积累和界面非辐射复合。然而，仅通过在钙钛矿薄膜中加入添加剂分子或在埋底界面处引入界面改性剂，很难同时解决上述问题和实现整体载流子管理。

鉴于此，重庆大学陈江照研究员、臧志刚教授及南方科技大学许宗祥副教授等人提出了一种由多种化学键协同诱导的自下而上的整体载流子管理策略，以最大限度地减少高效钙钛矿太阳能器电池的体相和界面能量损失。该策略是通过将含有丰富官能团（-CF₃、–NH₂–C=NH₂⁺和Cl^-）的4-三氟甲基苯甲脒盐酸盐（TBHCl）直接加入到SnO₂胶体溶液中来实现的，并且还将仅含有-CF₃的三氟甲苯（BTF）和仅含有甲脒阳离子和Cl^-阴离子的苯甲脒盐酸盐（BHCl）用作对照分子，以揭示目标分子中每个官能团的功能。结果表明，F和Cl^-均可以通过与Sn⁴⁺配位钝化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可以通过与FA⁺形成氢键来抑制阳离子迁移和调节结晶，并且可以通过与Pb²⁺配位来钝化铅缺陷。–NH₂–C=NH₂⁺和Cl^-可分别通过与钙钛矿形成离子键和/或静电相互作用来钝化阳离子和卤素阴离子空位缺陷。总之，目标分子中的各个官能团各司其职，展现了良好的协同作用，从而实现了多键诱导的自下而上的整体载流子管理。通过TBHCl改性，抑制了SnO₂纳米粒子的团聚、钝化了ETL中的氧空位缺陷和钙钛矿薄膜中的缺陷以及释放了钙钛矿膜中的拉伸应变，从而将PCE从21.28%提高到23.40%。结合PEAI钝化，效率进一步提高到23.63%。TBHCl改性器件具有优异的热和湿度稳定性。该工作为开发由多种化学键协同诱导的自下而上的整体载流子管理策略来提升器件的效率和稳定性提供了借鉴，为钙钛矿太阳能电池的商业化应用奠定了坚实的基础。

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.