Najafi Leyla, Taheri Babak, Martín-García Beatriz, Bellani Sebastiano, Di Girolamo Diego, Agresti Antonio, Oropesa-Nuñez Reinier, Pescetelli Sara, Vesce Luigi, Calabrò Emanuele, Prato Mirko, Del Rio Castillo Antonio E, Di Carlo Aldo, Bonaccorso Francesco
Graphene Labs , Istituto Italiano di Tecnologia , Via Morego 30 , 16163 Genova , Italy.
C.H.O.S.E. (Centre for Hybrid and Organic Solar Energy), Department of Electronic Engineering , University of Rome Tor Vergata , Via del Politecnico 1 , 00133 Rome , Italy.
ACS Nano. 2018 Nov 27;12(11):10736-10754. doi: 10.1021/acsnano.8b05514. Epub 2018 Sep 21.
Interface engineering of organic-inorganic halide perovskite solar cells (PSCs) plays a pivotal role in achieving high power conversion efficiency (PCE). In fact, the perovskite photoactive layer needs to work synergistically with the other functional components of the cell, such as charge transporting/active buffer layers and electrodes. In this context, graphene and related two-dimensional materials (GRMs) are promising candidates to tune "on demand" the interface properties of PSCs. In this work, we fully exploit the potential of GRMs by controlling the optoelectronic properties of molybdenum disulfide (MoS) and reduced graphene oxide (RGO) hybrids both as hole transport layer (HTL) and active buffer layer (ABL) in mesoscopic methylammonium lead iodide (CHNHPbI) perovskite (MAPbI)-based PSCs. We show that zero-dimensional MoS quantum dots (MoS QDs), derived by liquid phase exfoliated MoS flakes, provide both hole-extraction and electron-blocking properties. In fact, on one hand, intrinsic n-type doping-induced intraband gap states effectively extract the holes through an electron injection mechanism. On the other hand, quantum confinement effects increase the optical band gap of MoS (from 1.4 eV for the flakes to >3.2 eV for QDs), raising the minimum energy of its conduction band (from -4.3 eV for the flakes to -2.2 eV for QDs) above the one of the conduction band of MAPbI (between -3.7 and -4 eV) and hindering electron collection. The van der Waals hybridization of MoS QDs with functionalized reduced graphene oxide (f-RGO), obtained by chemical silanization-induced linkage between RGO and (3-mercaptopropyl)trimethoxysilane, is effective to homogenize the deposition of HTLs or ABLs onto the perovskite film, since the two-dimensional nature of RGO effectively plugs the pinholes of the MoS QD films. Our "graphene interface engineering" (GIE) strategy based on van der Waals MoS QD/graphene hybrids enables MAPbI-based PSCs to achieve a PCE up to 20.12% (average PCE of 18.8%). The possibility to combine quantum and chemical effects into GIE, coupled with the recent success of graphene and GRMs as interfacial layer, represents a promising approach for the development of next-generation PSCs.
有机-无机卤化物钙钛矿太阳能电池（PSC）的界面工程在实现高功率转换效率（PCE）方面起着关键作用。事实上，钙钛矿光活性层需要与电池的其他功能组件协同工作，如电荷传输/活性缓冲层和电极。在这种情况下，石墨烯及相关二维材料（GRM）有望“按需”调节PSC的界面性质。在这项工作中，我们通过控制二硫化钼（MoS）和还原氧化石墨烯（RGO）杂化物作为介观甲基碘化铅（CH₃NH₃PbI）钙钛矿（MAPbI）基PSC的空穴传输层（HTL）和活性缓冲层（ABL）的光电性质，充分发挥了GRM的潜力。我们表明，由液相剥离的MoS薄片衍生的零维MoS量子点（MoS QD）兼具空穴提取和电子阻挡特性。事实上，一方面，本征n型掺杂诱导的带内隙态通过电子注入机制有效地提取空穴。另一方面，量子限域效应增加了MoS的光学带隙（从薄片的1.4 eV增加到量子点的>3.2 eV），将其导带的最小能量（从薄片的-4.3 eV增加到量子点的-2.2 eV）提高到高于MAPbI导带的能量（在-3.7和-4 eV之间），从而阻碍电子收集。通过化学硅烷化诱导RGO与（3-巯基丙基）三甲氧基硅烷之间的连接获得的MoS QD与功能化还原氧化石墨烯（f-RGO）的范德华杂交，有效地使HTL或ABL在钙钛矿薄膜上的沉积均匀化，因为RGO的二维性质有效地堵塞了MoS QD薄膜的针孔。我们基于范德华MoS QD/石墨烯杂化物的“石墨烯界面工程”（GIE）策略使基于MAPbI的PSC能够实现高达20.12%的PCE（平均PCE为18.8%）。将量子和化学效应结合到GIE中的可能性，再加上石墨烯和GRM作为界面层最近取得的成功，代表了一种开发下一代PSC的有前途的方法。
