Applications of Self‐Assembled Monolayers for Perovskite Solar Cells Interface Engineering to Address Efficiency and Stability

Abstract

the majority of the market shares as compared to next-generation thin-film PV technologies. Nevertheless, technological challenges in improving efficiencies and decreasing the high-energy requirements connected to the fabrication of silicon PV results in a higher global warming potential. In an effort to achieve lower fabrication cost and higher efficiencies, different types of thin-film PV technologies have been developed including dyesensitized solar cells, [2,3] organic solar cells, [4,5] copper indium tin sulfur [6,7] and emerging organic-inorganic lead halide perovskite solar cells (PSCs). [8,9] The combined merits of low fabrication cost and high power conversion efficiency (PCE) are distinct features of PSCs where PCE has jumped from 3.8% [8] to 25.2% [10] in just a decade. Such a sharp increase in PCE is mainly attributed to the large absorption coefficient, [11] long carrier lifetime, [12] high trap resistance, [13] high dielectric constant, [14-16] low binding energy, [17] and tunable bandgap of 1.2−1.7 eV, [18] all combined in a single perovskite material. 1.1. Perovskite Solar Cell Device Structures A typical perovskite solar cell consists of a light-absorbing perovskite layer which is sandwiched between an electron transport layer (ETL) and a hole transport layers (HTL). To complete the device, ETL is supported on a transparent conducting oxide (TCO) front electrode, and HTL on metal-coated back contact electrode, Figure 1. There are two basic structures for the PSC: the so-called mesoporous structure, which contains a mesoporous ETL layer (i.e., mesoporous TiO 2), and the planar structure, as depicted in Figure 1a,b. Even though early reports based on mesoporous devices assumed that the perovskite infiltration through the mesoporous scaffold improved the charge carrier collection to the electrode, later investigations performed by Lee and co-workers replaced the TiO 2 with an insulating Al 2 O 3 mesoporous layer, and reported for the first time the ambipolar nature of the perovskite materials, allowing the realization of longer diffusion length. [19] This enabled the fabrication of planar devices, and gave rise to an impressive evolution of device architectures, novel materials and cell configurations either in n-i-p or p-in designs. [12,19,20] In addition, Due to a certified 25.2% high efficiency, low cost, and easy fabrication; perovskite solar cells (PSCs) are the focus of interest among the nextgeneration photovoltaic technologies. Long-term stability is one of the most challenging obstacles to bring technology from the lab to the market. In this review, applications of self-assembled monolayers (SAMs) to enhance the power conversion efficiency (PCE) and stability of PSCs is discussed. In the first part, the introduction of SAMs, and deposition techniques applied to different PSC architectures are described. In the middle section, current efforts to utilize SAMs to fine-tune the optoelectronic properties to enhance the PCE and stability are detailed. The improvements in surface morphology, energ...

NiOx‐Seeded Self‐Assembled Monolayers as Highly Hole‐Selective Passivating Contacts for Efficient Inverted Perovskite Solar Cells

“…[ 24 ] Typically, SAMs usually consist of rod‐like molecules comprising an anchoring group, mediating the bonding to a specific substrate, a tail (functional) group, governing the deposition of the forthcoming layer and altering the energy level offset at the interface, and a spacer group, connecting both groups and building the SAM matrix. [ 25 ] Based on the interaction such as electrostatic, hydrogen bonding, charge transfer, and covalent bonding, the SAMs can be physisorbed or chemisorbed from solution onto various surfaces and form extremely thin layers, by solution‐processed methods such as spin, blade, dip, spray, and slot‐die coating. [ 26 ]…”

“…[24] Typically, SAMs usually consist of rod-like molecules comprising an anchoring group, mediating the bonding to a specific substrate, a tail (functional) group, governing the deposition of the forthcoming layer and altering the energy level offset at the interface, and a spacer group, connecting both groups and building the SAM matrix. [25] Based on the interaction such as electrostatic, hydrogen DOI: 10.1002/solr.202100663 Self-assembled monolayers (SAMs) have emerged as effective carrier transport layers in perovskite (PVK) solar cells because of their unique ability to manipulate interfacial property, as well as simple processing and scalable fabrication. However, the defects and pinholes derived from their sensitive adsorption process inevitably deteriorate the final device performance.…”

Effect of surface modification of nickel oxide hole‐transport layer via self‐assembled monolayers in perovskite solar cells

“…As the device power conversion efficiency is a composite result of open circuit voltage (V oc ), short circuit current (J sc ) and fill factor (FF), which can all affected by the morphology/crystallinity of perovskite and its contact with other layers and in turn be modulated by SAM modification, minimizing the number of variables involved may lead to better correlation. [39,40] Here in this report, we modified the nickel oxide surface with a series of para-substituted phenylphosphonic acid SAMs as the HTL in the fabrication of PSC to investigate their effect on the device performance. The different substituents (electron-donating CH 3 O-, H-and electronwithdrawing CN-groups) impart different molecular dipoles to the molecules so that when anchored to the NiO x surface, the work function (WF) of the NiO x HTL can be tuned with respect to the valence level of the perovskite layer.…”

Current Status of Emerging PV Technologies: A Comparative Study of Dye-Sensitized, Organic, and Perovskite Solar Cells

“…Bush et al [90] reported a power conversion efficiency of 23.6% for a monolithic perovskite/silicon tandem cell that operated successfully for 1000 hours under a damp heat test (85°C and 85% relative humidity). In addition, self-assembled monolayers, which are ordered arrays of organic molecules, have been utilized as interfacial layers in PSCs, in order to improve their efficiency and stability [91].…”