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MoS2 Quantum Dot/Graphene Hybrids for Advanced Interface Engineering of a CH3NH3PbI3 Perovskite Solar Cell with an Efficiency of over 20%
journal contribution
posted on 2018-09-21, 19:48 authored by Leyla Najafi, Babak Taheri, Beatriz Martín-García, Sebastiano Bellani, Diego Di Girolamo, Antonio Agresti, Reinier Oropesa-Nuñez, Sara Pescetelli, Luigi Vesce, Emanuele Calabrò, Mirko Prato, Antonio E. Del Rio Castillo, Aldo Di Carlo, Francesco BonaccorsoInterface 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
(MoS2) and reduced graphene oxide (RGO) hybrids both as
hole transport layer (HTL) and active buffer layer (ABL) in mesoscopic
methylammonium lead iodide (CH3NH3PbI3) perovskite (MAPbI3)-based PSCs. We show that zero-dimensional
MoS2 quantum dots (MoS2 QDs), derived by liquid
phase exfoliated MoS2 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 MoS2 (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 MAPbI3 (between −3.7 and −4 eV) and
hindering electron collection. The van der Waals hybridization of
MoS2 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
MoS2 QD films. Our “graphene interface engineering”
(GIE) strategy based on van der Waals MoS2 QD/graphene
hybrids enables MAPbI3-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.
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Keywords
CH 3 NH 3 PbI 3 Perovskite Solar Cellconduction bandn-type doping-induced intraband gap statesvan der Waals hybridizationpower conversion efficiencyAdvanced Interface EngineeringPCEMoS 2 QDsgraphene oxideMoS 2eVquantum confinement effects increasechemical silanization-induced linkageGRMPSChole transport layerHTLphase exfoliated MoS 2 flakesperovskite photoactive layerzero-dimensional MoS 2 quantum dotsGIEMAPbI 3MoS 2 QD filmsRGOelectron injection mechanismCH 3 NH 3 PbI 3ABL
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