MoS2 Quantum Dot/Graphene Hybrids for Advanced Interface Engineering of CH3NH3PbI3 Perovskite Solar Cell with Efficiency over 20% (1903.08954v1)

Abstract: Interface engineering of organic-inorganic halide perovskite solar cells (PSCs) plays a pivotal role in achieving high power conversion efficiency (PCE). 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 hybrids between molybdenum disulfide (MoS2) and reduced graphene oxide (RGO) as hole transport layer (HTL) and active buffer layer (ABL) in mesoscopic methylammonium lead iodide (CH3NH3PbI3) perovskite (MAPbI3)-based PSC. 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 the one hand, intrinsic n-type doping-induced intra-band 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 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 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 (2D) nature of RGO effectively plug the pinholes of the MoS2 QDs films. Our graphene interface engineering (GIE) strategy based on van der Waals MoS2 QD/graphene hybrids enable MAPbI3-based PSCs to achieve PCE up to 20.12% (average PCE of 18.8%).

Analysis of MoS₂ Quantum Dot/Graphene Hybrids for Perovskite Solar Cell Efficiency Enhancement

The paper by Najafi et al. focuses on advanced interface engineering techniques employing molybdenum disulfide (MoS₂) quantum dots and reduced graphene oxide (RGO) in perovskite solar cells (PSCs). The primary objective is enhancing power conversion efficiency (PCE) beyond 20% by optimizing the interfaces within the PSC architecture, notably using graphene-related materials (GRMs).

The researchers have synthesized zero-dimensional MoS₂ quantum dots through liquid phase exfoliation, subsequently leveraging their quantum confinement properties to achieve electronic structure modifications superior to traditional MoS₂ flakes. This quantum effect raises the conduction band energy in MoS₂ QDs, facilitating electron blocking and thus reducing interfacial recombination losses. These QDs are hybridized with chemically functionalized RGO, effectively addressing pinholes in the MoS₂ QD films due to the two-dimensional nature of RGO. This hybridization enhances the deposition quality of hole transport layers (HTL) or active buffer layers (ABL).

The paper presents strong numerical results, indicating a maximum PCE of 20.12% with an average of 18.8%, alluding to promising advancements in interface engineering with GRMs. Significant improvements in carrier collection—shown by an increase in J from 20.28 mA/cm² to 22.81 mA/cm²—further validate the compatibility and efficiency of the MoS₂ QD:f-RGO hybrid layers.

Implications of this research stretch beyond efficiency enhancement and encompass potential stability improvements of PSCs. The findings suggest that strategic hybridization of materials like MoS₂ QD and functionalized RGO could mitigate ion migration issues, a critical factor affecting PSC longevity and performance.

The paper acknowledges existing stability challenges inherent in the MAPbI₃ perovskite due to environmental factors and suggests that interface engineering using 2D materials presents a viable route to address these issues. As such, the inclusion of GRMs into PSC architectures may serve as a cornerstone for future developments toward more stable perovskite devices.

The exploration of MoS₂ QDs and RGO hybrids constitutes an important step in integrating quantum-chemical effects within photovoltaic materials, offering a promising pathway toward the development of next-generation PSCs that effectively utilize interface engineering for enhanced photovoltaic performance.