Rational Design of Dipolar Chromophore as an Efficient Dopant-Free Hole-Transporting Material for Perovskite Solar Cells

In this paper, an electron donor–acceptor (D-A) substituted dipolar chromophore (BTPA-TCNE) is developed to serve as an efficient dopant-free hole-transporting material (HTM) for perovskite solar cells (PVSCs). BTPA-TCNE is synthesized via a simple reaction between a triphenylamine-based Michler’s base and tetracyanoethylene. This chromophore possesses a zwitterionic resonance structure in the ground state, as evidenced by X-ray crystallography and transient absorption spectroscopies. Moreover, BTPA-TCNE shows an antiparallel molecular packing (i.e., centrosymmetric dimers) in its crystalline state, which cancels out its overall molecular dipole moment to facilitate charge transport. As a result, BTPA-TCNE can be employed as an effective dopant-free HTM to realize an efficient (PCE ≈ 17.0%) PVSC in the conventional n-i-p configuration, outperforming the control device with doped spiro-OMeTAD HTM.

本研究开发了一种带有电子给体-受体（electron donor–acceptor，D-A）结构的偶极生色团（dipolar chromophore）BTPA-TCNE，用作钙钛矿太阳能电池（perovskite solar cells，PVSCs）的高效无掺杂空穴传输材料（hole-transporting material，HTM）。BTPA-TCNE通过三苯胺类米氏碱与四氰基乙烯的简单反应合成。该生色团基态下具备两性离子共振结构，该结构经X射线晶体学与瞬态吸收光谱表征证实。此外，BTPA-TCNE在晶态下呈现反平行分子堆积（即中心对称二聚体），可抵消整体分子偶极矩以促进电荷传输。最终，BTPA-TCNE可作为高效无掺杂HTM，在常规n-i-p结构的钙钛矿太阳能电池中实现约17.0%的光电转换效率（PCE），其性能优于采用掺杂spiro-OMeTAD作为空穴传输材料的对照器件。