引言#

倒置钙钛矿太阳能电池凭借良好的加工兼容性和出色的稳定性，近年来成为光伏研究领域的焦点。咔唑膦酸类自组装单层膜作为高效空穴传输界面材料，能够有效钝化界面缺陷并促进载流子抽取。然而在自组装形成单层膜的过程中，分子受限于基底作用力与空间位阻，其分子取向往往难以精确控制。这种混乱或非理想的取向会导致界面偶极减弱以及电荷传输选择性下降，成为限制电池效率和长期运行稳定性的关键瓶颈。因此，如何从分子结构源头出发，探索出能够精确引导分子在基底上呈有序取向的化学合成新策略，是该领域亟待解决的核心科学问题。

Fig.1 (a) Structures of isomers of (9H,9′H-bicarbazole]-9,9′-diylbis(propane-3,1-diyl))bis (phosphonic acid) and schematic diagram of carbazole rotation around the bridge bond for conformational energy calculations (taking BCz-4 as an example); (b) Energy levels calculated for BCz-4’s conformations at different dihedral angles (the initial angle was set to 0°); (c) Distribution of carbazole-carbazole dihedral angles for the four SAMs in stable conformations; (d) X-ray crystallographic structures of four target SAMs (hydrogens are omitted for clarity); (e) Electrostatic surface potentials and dipole moments of the four SAMs (cis-conformers of BCz-2 and BCz-3 are shown in Figure S21); (f) Theoretical adsorption modes and charge-density differences of the four SAMs on ITO.

主要实验及结论#

研究人员通过调控异构双咔唑主链上的连接位点，设计并合成了一系列双膦酸咔唑衍生分子。正如图1所示，理论计算表明咔唑环之间的旋转阻尼不同导致了截然不同的分子构型。其中BCz-4分子呈现独特的顺式构型，其两个末端膦酸锚定基团位于咔唑骨架的同一侧。这种特殊的顺式构型赋予了BCz-4分子在氧化铟锡基底上更强的双足吸附能力，其吸附能达到-6.03 eV，远高于其他反式或扭曲异构分子的吸附强度，大幅缩短了分子与基底之间的界面间距并增强了电子转移能力。

在界面组装与取向调控的实验测试中，图2展现了不同自组装单层膜的表面特性差异。水接触角测试表明，具有顺式双足结构的BCz-4膜层展现出最高的表面疏水性。结合和频光谱以及角分辨X射线光电子能谱分析，研究团队证实了BCz-4分子在基底表面呈现高度有序的直立侧向取向，而其他异构体则倾向于平躺或无序排列。这种立式排列方式使得双膦酸基团牢固锚定在基底表面，而将咔唑核心暴露于外侧，显著改善了膜层的均匀性与覆盖率。

Fig.2 (a) Water contact angles on SAM-modified ITO. (b) The ssp combination SFG spectra for quartz/SAMs in the range of 2800 to 3200 cm−1, where the gray box indicates the C–H υ2 stretching vibration peak of the benzene ring; (c) Calibration of the ssp/ppp SFG susceptibility ratio against molecular tilt angle (solid curve) and the resulting orientations of BCz-1–BCz-4 (stars). Inset: schematic of the tilt angle geometry on the ITO substrate. (d) Adhesion-force curves of SAMs on ITO. (e) Schematic orientation of SAMs on ITO relative to the perovskite layer.

研究人员进一步通过开尔文探针力显微镜和光电性能表征深入探讨了能级对齐与载流子动力学。如图3所示，BCz-4修饰后的基底功函数得到了最大程度的提升，形成了更加匹配的界面能级阶梯。这不仅显著降低了界面处的非辐射复合损失，还极大提高了空穴抽取速率。飞秒瞬态吸收光谱测试证明，BCz-4界面层使得激子转移效率大幅提高，有效抑制了界面积累电荷对电池电压的损耗。

Fig.3 (a) KPFM images and contact-potential maps of SAM-modified ITO films; (b) Surface contact potential difference (CPD) of SAM-on-ITO samples; (c) XPS spectra showing Sn 3d peaks of SAMs-modified ITO; (d) UPS spectra of SAM-modified ITO films; (e) Energy-level alignment schematic (EF: Fermi level, EVAC: vacuum level; EVBM: valence-band maximum).

在电池器件测试环节，基于BCz-4自组装单层膜构建的倒置钙钛矿太阳能电池展现出了卓越的光电性能。器件获得了高达27.2% 的认证光电转换效率，该数值处于目前单结倒置钙钛矿电池的顶尖水平。同时，由于双足锚定结构带来的强化学键合作用，器件具有极高的耐湿热与光照稳定性。在空气环境大面积刮涂制备中，该材料同样表现出优异的工艺兼容性。在1个标准太阳光照及最大功率点追踪的连续测试下，器件运行1400小时后仍能维持初始效率的96%。

Fig.4 (a) J-V curves of the best performing spin-coated PSCs fabricated under N2; (b) EQE spectra and integrated JSC curves of the corresponding PSCs; (c) MPP tracking of encapsulated bare-ITO control, 3PACz-control, and BCz-4-modulated PSCs at 25 ± 3°C in air under 1-sun illumination; (d) TRPL spectra of perovskite films on SAMs (solid lines: bi-exponential fits); (e) Dark J–V characteristics of hole-only devices (ITO/SAM/Perovskite/PTAA/Ag) with different SAMs; (f) J–V characteristics of best-performing PSCs fabricated by blade-coating protocol in ambient conditions; (g) Comparison of electronic properties across SAM molecular orientation: charge carrier mobility, work function, and photovoltaic efficiency. (h) Simulated J-V curves via SCAPS-1D based on different hole mobilities and work functions of the SAM layer.

总结与展望#

本项研究阐明了分子构型对自组装单层膜取向及界面光电特性的调控机制。通过精细设计双咔唑连接位点，成功开发出具备高吸附能与优异分子取向的双膦酸自组装材料。这项成果不仅刷新了倒置钙钛矿太阳能电池的效率记录，也为解决界面稳定性和大面积制备难题提供了重要指导。未来，基于这种分子构型调控的化学策略有望拓展至更多光电器件的界面工程中，加速推动钙钛矿光伏技术的商业化产业进程。