Role of self-assembled molecules in halide perovskite optoelectronics: an atomic-scale perspective

Abstract

Despite significant advancements in the study of metal halide perovskites worldwide, the large-scale industrialization of related optoelectronic devices faces ongoing challenges related to efficiency, long-term stability, and environmental and human toxicity. Self-assembled molecules (SAMs) have recently emerged as crucial strategies for enhancing device performance and stability, particularly by mitigating interface-related challenges. This review provides a comprehensive examination of the multifaceted roles of SAMs in enhancing the performance and stability of perovskite optoelectronic devices. We begin by introducing the evolution of SAMs, their unique physicochemical properties and implemented applications in optoelectronic devices. Subsequently, we delve into the diverse beneficial effects of SAMs in perovskite devices and elucidate the underlying atomic-scale mechanisms responsible for these performance enhancements. Finally, we critically analyze the current challenges associated with the rational design and implementation of SAMs in perovskite devices and conclude by outlining promising future research directions.

Keywords: atomic-scale mechanism; halide perovskites; interface engineering; optoelectronics; self-assembled molecules.

Figure 1.

Four modes of SAM application in perovskite optoelectronic devices (middle panel), along with their associated effects and corresponding atomic-scale mechanisms. (a) Optimization of interfacial charge transport through defect passivation and energy level alignment. Adapted with permission from [17] and [16]. Copyright 2020, Royal Society of Chemistry. Copyright 2017, Wiley-VCH. (b) Regulation of interfacial wettability and uniformity via surface energy modulation and control of crystal growth. Adapted with permission from [18] and [19]. Copyright 2019, Wiley-VCH. Copyright 2015, American Chemical Society. (c) Enhancement of interfacial mechanical strength and alleviation of interfacial stress through improved contact and flexible connections. Adapted with permission from [21] and [20]. Copyright 2021, American Association for the Advancement of Science. Copyright 2023, Springer Nature. (d) Improvement of interfacial chemical stability through physical isolation and chemical anchoring. Adapted with permission from [22] and [23]. Copyright 2020, Springer Nature. Copyright 2024, Wiley-VCH. CB: conduction band; VB: valence band; CTL: charge transport layer; TCO: transparent conductive oxide; PVK: perovskite.

Figure 2.

Representative examples of terminal groups, linker groups and anchoring groups in SAMs as reported in the literature (a–c), along with the intrinsic advantages of each type of functional group (d–f).

Figure 3.

Experimental techniques used to observe the enhancement of charge transport, wettability and uniformity in perovskite optoelectronic devices by SAMs. (a) Schematic diagram of interfacial charge transport. Adapted with permission from [64]. Copyright 2022, Wiley-VCH. (b) Photoluminescence spectra. Adapted with permission from [65]. Copyright 2022, Springer Nature. (c) Time-resolved photoluminescence. Adapted with permission from [67]. Copyright 2020, American Association for the Advancement of Science. (d) Quasi-Fermi level splitting. Adapted with permission from [35]. Copyright 2023, Springer Nature. (e) Schematic diagram of wettability. Adapted with permission from [18]. Copyright 2019, Wiley-VCH. (f–h) Effect of SAM anchoring on the contact angle of the ultrathin Au layer. Adapted with permission from [49]. Copyright 2021, American Chemical Society. (i) Schematic diagram of uniformity. Adapted with permission from [74]. Copyright 2018, Springer Nature. (j) Atomic force microscopy. Adapted with permission from [75]. Copyright 2018, American Chemical Society. (k) Photoluminescence mapping. Adapted from [43], licensed under CC BY 4.0.

Figure 4.

Experimental techniques used to observe the effects of SAMs on interfacial stress release, enhancement of mechanical strength, and suppression of chemical reactions and phase segregation in perovskite optoelectronic devices. (a) Schematic diagram of interfacial stress. Adapted with permission from [76]. Copyright 2022, American Chemical Society. (b, c) Grazing incidence X-ray diffraction. Adapted with permission from [77]. Copyright 2022, Wiley-VCH. Adapted from [78], licensed under CC BY 4.0. (d) Williamson-Hall method. Adapted with permission from [79]. Copyright 2023, Elsevier. (e) Schematic diagram of mechanical strength. Adapted with permission from [80]. Copyright 2021, Elsevier. (f, g) Double-cantilever beam method. Adapted with permission from [21]. Copyright 2021, American Association for the Advancement of Science. (h) Fixed-radius bending method. Adapted with permission from [65]. Copyright 2022, Springer Nature. (i) Schematic diagram of chemical reactions. Adapted from [82], licensed under CC BY 4.0. (j) X-ray diffraction. Adapted with permission from [77]. Copyright 2022, Wiley-VCH. (k) X-ray photoelectron spectroscopy. Adapted with permission from [85]. Copyright 2023, Wiley-VCH. (l) Photoluminescence peak shifts. Adapted with permission from [67]. Copyright 2020, American Association for the Advancement of Science.

Figure 5.

The atomic-scale mechanism by which SAMs optimize charge transport through defect passivation and energy level alignment modulation. (a, b) The defect passivation effects of the terminal groups (a) and anchoring groups (b) of SAMs. Adapted with permission from [69], [89] and [55]. Copyright 2023, Elsevier. Copyright 2023, Wiley-VCH. Copyright 2023, American Association for the Advancement of Science. (c) Modulation of energy level alignment through the design of SAM terminal groups and anchoring groups. Adapted with permission from [16] and [92]. Copyright 2017, Wiley-VCH. Copyright 2024, Wiley-VCH. (d) Continuous modulation of energy level alignment through the mixed use of SAMs with different dipoles. Adapted with permission from [65]. Copyright 2022, Springer Nature.

Figure 6.

Atomic-scale mechanisms by which SAMs regulate wettability, uniformity, stress and mechanical strength, and enhance chemical stability at the interface. (a) Regulation of surface energy (E_surface) through amphiphilic properties. Adapted with permission from [55]. Copyright 2023, American Association for the Advancement of Science. (b) Crystal growth regulation. Adapted with permission from [19]. Copyright 2015, American Chemical Society. (c) Enhancement of contact by adding additional interfacial chemical bonds. Adapted with permission from [21]. Copyright 2021, American Association for the Advancement of Science. (d) Stress relief through molecular flexibility. Adapted with permission from [20]. Copyright 2023, Springer Nature. (e) Prevention of moisture-induced corrosion using hydrophobic groups. Adapted with permission from [14]. Copyright 2020, Royal Society of Chemistry. (f) Blocking ion and molecular migration through the steric effects of a densely assembled layer. Adapted with permission from [104]. Copyright 2024, Royal Society of Chemistry. (g, h) Inhibition of ion migration through surface (g) and bridging (h) chemical anchoring. Adapted with permission from [105] and [23]. Copyright 2022, Wiley‐VCH. Copyright 2024, Wiley‐VCH.