Zu Fengshuo, Wang Rongbin, Frohloff Lennart, Zorn-Morales Nicolas, Blumstengel Sylke, List-Kratochvil Emil, Amsalem Patrick, Koch Norbert
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, 12489 Berlin, Germany.
Institut für Physik & Center for the Science of Materials Berlin, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.
ACS Appl Mater Interfaces. 2025 May 21;17(20):30251-30258. doi: 10.1021/acsami.5c02989. Epub 2025 May 12.
van der Waals (vdW) heterojunctions offer many routes for advanced interface engineering toward superior optoelectronic functionality. To this end, the combination of 2D transition metal dichalcogenides (TMDCs) with metal halide perovskites has shown great potential for applications in photovoltaics and photodetectors. The electronic energy level alignment at such heterojunctions, i.e., the relative alignment of valence and conduction bands of the two materials, is crucial for their functionality, but its experimental determination is notoriously challenging. In this contribution, we determine the energy level alignment for the vdW heterojunction composed of monolayer molybdenum disulfide (ML-MoS) and a triple cation-mixed halide perovskite, enabled by surface cleaning by argon cluster sputtering. This effectively removes surface contaminants from the perovskite/ML-MoS stack without causing damage, enabling direct determination of the band alignment at the interface using ultraviolet and X-ray photoelectron spectroscopy. Our results reveal a type-II band alignment at the perovskite/ML-MoS interface. Importantly, the interfacial energy levels are not fixed once the heterojunction is formed, but the MoS energy levels shift relative to those of the perovskite under 1 sun illumination compared to the dark, by up to 0.25 eV. This energy level realignment, under conditions mimicking a photovoltaic device under operation, is attributed to photogenerated electron accumulation in the ML-MoS. Microscopic photoluminescence (PL) measurements reveal significant quenching of the perovskite PL signal in the heterojunction, confirming efficient charge transfer and the establishment of a type-II heterojunction. These results demonstrate a "living" heterojunction energy landscape, opening up novel avenues for engineering perovskite/TMDCs vdW heterojunctions for optoelectronic devices.
范德华（vdW）异质结为实现卓越的光电功能提供了许多先进界面工程的途径。为此，二维过渡金属二硫属化物（TMDCs）与金属卤化物钙钛矿的组合在光伏和光电探测器应用中显示出巨大潜力。这种异质结处的电子能级排列，即两种材料的价带和导带的相对排列，对其功能至关重要，但其实验测定极具挑战性。在本论文中，我们通过氩团簇溅射进行表面清洁，确定了由单层二硫化钼（ML-MoS）和三阳离子混合卤化物钙钛矿组成的vdW异质结的能级排列。这有效地去除了钙钛矿/ML-MoS叠层表面的污染物而不造成损伤，从而能够使用紫外和X射线光电子能谱直接测定界面处的能带排列。我们的结果揭示了钙钛矿/ML-MoS界面处的II型能带排列。重要的是，一旦形成异质结，界面能级并非固定不变，而是与黑暗条件相比，在1个太阳光照下，MoS能级相对于钙钛矿能级最多偏移0.25 eV。这种在模拟工作中的光伏器件的条件下的能级重新排列，归因于光生电子在ML-MoS中的积累。微观光致发光（PL）测量揭示了异质结中钙钛矿PL信号的显著猝灭，证实了有效的电荷转移以及II型异质结的形成。这些结果展示了一种“动态”的异质结能量态势，为设计用于光电器件的钙钛矿/TMDCs vdW异质结开辟了新途径。
