Chiral Hybrid Perovskites for Direct Circularly Polarized Photodetectors
手性雜化金屬鈣鈦礦用於直接圓偏光探測器
Student thesis: Doctoral Thesis
Author(s)
Related Research Unit(s)
Detail(s)
| Awarding Institution | |
|---|---|
| Supervisors/Advisors |
|
| Award date | 4 Nov 2024 |
Link(s)
| Permanent Link | https://scholars.cityu.edu.hk/en/theses/theses(480dd394-d00f-408a-8ab8-10e11a7f067a).html |
|---|---|
| Other link(s) | Links |
Abstract
Tracking back over the past decade, metal halide perovskites became one of the most popular semiconductor materials studied in various areas, such as light-emitting diodes, solar cells, lasers, spintronics, optical communication, chemical catalysis, biomedical sensing, environmental monitoring and so forth. Such popularity of state-of-the-art multifunctional perovskites has benefited from their outstanding optoelectronic properties, including broad, tunable, and strong light absorption, superior charge transport, efficient free charge carrier generation, excellent photoluminescence, high dielectric constant, low binding energy, and low-cost, large-scale solution-processability. On the other hand, chirality, an intrinsic feature that exists in nature, has been attracting tremendous interest of scientists since a long time. While we can combine the outstanding light absorption properties of perovskites and the intrinsic chiral selectivity of chiral materials, we can realize direct circularly polarized photodetection. Conventionally, circularly polarized light detection requires a linear polarizer and a quarter waveplate properly aligned and combined with a photodetector device. The complexity of operation and additional optical components introduced during this process both add difficulty in operation and reduce detected light intensity. Chiral perovskites are thus potential candidates for direct circularly polarized photodetection, especially when these materials have an intrinsic broad-range superior light absorption and strong chiral selectivity. Apart from that, the optical and magnetic properties of the same chiral perovskite semiconductors can enable spin electronics, spin light-emitting diodes, and spin memory devices.
In the first chapter of this thesis, a comprehensive review of chirality is introduced, with the timeline starting from antiquity around 250 BC, up until recent optical developments. In 1893, the notion of a chiral object and the concept of ‘Chirality’ was introduced by Lord Kelvin, one of the most eminent scientists of the 19th century. The Archimedes Screw was eventually the first chiral concept, while after that, the phenomenon of light polarization was observed in quartz crystals and sugar solutions. Then para-tartaric acid was found to exhibit chiral asymmetry, with different enantiomers of this molecule shown to be able to distinguish differently polarized light. The next significant breakthrough was the discovery of liquid crystals, which opened up the era of liquid crystal displays based largely on nematic liquid crystals, though the seminal work was on their chiral nematic (cholesteric) cousins Chiral properties were later discovered in biology and physics, such as the DNA double-helix and parity non-conservation phenomena, respectively. In material science, three categories of chiral materials were introduced sequentially, namely organic chiral materials, inorganic chiral materials, and hybrid organic-inorganic chiral materials. Among those, the chiral organic-inorganic metal halide perovskites are considered in detail in this thesis.
The parameters and the characteristics of chiral properties and the corresponding applications are introduced in Chapter 2. The fundamental concept of light polarization is explained based on the concepts of linear polarization and circular polarization including right- and left-hand circularly polarized light. Circular dichroism is one of the key features of chiral materials, which reflects the absorbance difference when they are illuminated by left- and then right-handed circularly polarized light. The basic definition of circular dichroism and the principle of circular dichroism measurements using various approaches are considered. Another vital feature of chiral materials is their circularly polarized luminescence, which is elucidated according to the fundamental definition and theories, along with the corresponding experimental methodologies. In addition, chiral materials can also manifest chiral-induced spin selectivity, non-linear chiroptical effects, and ferroelectric properties and these are illustrated in this chapter accordingly. Moreover, two important application configurations, photodetectors and field effect transistors (FETs) are introduced based on their working principles and parameter analysis, followed by the related experiment studies of such devices based on chiral organic-inorganic halide perovskites, which can form the basis for direct circularly polarized photodetectors, light-emitting diodes, spin photogalvanic, and spintronic devices.
The following three chapters (Chapter 3-5) present three experimental studies conducted within this thesis. In Chapter 3, organic-inorganic (hybrid) metal halide perovskites (MHPs) incorporating chiral organic ligand molecules are shown to be naturally sensitive to left- and right-handed circular polarized light, potentially enabling selective circular polarized photodetection. The photoresponses in chiral MHP polycrystalline thin films made of ((S)-(−)-α-methyl benzylamine)2PbI4 and ((R)-(+)-α-methyl benzylamine)2PbI4, denoted as (S-MBA)2PbI4 and (R-MBA)2PbI4, respectively, are investigated by employing a thin-film field-effect transistor (FET) configuration. The left-hand-sensitive films made of (S-MBA)2PbI4 perovskite show higher photocurrent under left-handed circularly polarized (LCP) light than under right-handed circularly polarized (RCP) illumination under otherwise identical conditions. Conversely, the right-hand-sensitive films made of (R-MBA)2PbI4 are more sensitive to RCP than LCP illumination over a wide temperature range of 77–300 K. Furthermore, based on FET measurements, we found evidence of two different carrier transport mechanisms with two distinct activation energies in the 77–260 K and 280–300 K temperature ranges, respectively. In the former temperature range, shallow traps are dominant in the perovskite film, which is filled by thermally activated carriers with increasing temperature; in the latter temperature range, deep traps with one order of magnitude larger activation energy dominate. Both types of chiral MHPs show intrinsic p-type carrier transport behavior regardless of the handedness (S or R) of these materials. The optimal carrier mobility for both handedness of this material is found to be around (2.7 ± 0.2) × 10–7 cm2 V–1 s–1 at 270–280 K, which is two magnitudes larger than those reported previously for nonchiral perovskite MAPbI3 polycrystalline thin films. These findings suggest that chiral MHPs can be an excellent candidate for selective circular polarized photodetection applications, without additional polarizing optical components, enabling simplified construction of detection systems.
In Chapter 4, thin-film FETs based on chiral quasi-two-dimensional hybrid perovskites are explored, and the temperature dependence of the charge carrier transport mechanism over a broad temperature range (80–300 K) is revealed. A typical p-type charge transport behavior is observed for both left-handed (S-C6H5(CN2)2NH3)2(CH3NH3)n−1PbnI3n+1 and right-handed (R-C6H5(CN2)2NH3)2(CH3NH3)n−1PbnI3n+1 chiral perovskites, with maximum carrier mobilities of 1.7 × 10–5 cm2 V–1 s–1 and 2.5 × 10–5 cm2 V–1 s–1 at around 280 K, respectively. The shallow traps with smaller activation energy (0.03 eV) hinder the carrier transport over the lower temperature regime (80–180 K), while deep traps with one order of magnitude larger activation energy than the shallow traps moderate the charge carrier transport in the temperature range of 180–300 K. From the charge carrier mechanism point of view, impurity scattering is established as the dominant factor from 80 K until around 280 K, while in contrast, phonon scattering becomes predominant up to room temperature. Responsivities of 0.15 A W–1 and 0.14 A W–1 for left-handed and right-handed chiral perovskite FET devices are obtained.
In Chapter 5, yet another type of chiral (non-perovskite) material based on AgBiS2 nanocrystals is explored. Based on the developed chiral ligand exchange performed on AgBiS2 nanocrystals post-synthetically, a strong, long-lasting CD signal in the near-UV region is demonstrated. By carefully optimizing the ligand concentration, peak CD effects are observed at 260 and 320 nm, respectively, giving insight into the different ligand binding mechanisms influencing the CD signal in AgBiS2. The corresponding FET device performance of devices constructed with these materials illustrates the typical p-type carrier transport with 1.3× 10–3 cm2 V–1 s–1 for L-Cysteine treated AgBiS2 nanocrystals. This study represents a considerable advancement in the field of chiral nanocrystals and points toward their future applications.
Overall, this thesis provides several meaningful research studies of chiral perovskites and chiral AgBiS2 nanocrystals by illustrating their capability for use in direct circularly polarized photodetection and showing relevant FET performance to explore the underlying chiral charge carrier transport for a better understanding of the carrier transport mechanisms, which can be exploited to improve the device performance.
In the first chapter of this thesis, a comprehensive review of chirality is introduced, with the timeline starting from antiquity around 250 BC, up until recent optical developments. In 1893, the notion of a chiral object and the concept of ‘Chirality’ was introduced by Lord Kelvin, one of the most eminent scientists of the 19th century. The Archimedes Screw was eventually the first chiral concept, while after that, the phenomenon of light polarization was observed in quartz crystals and sugar solutions. Then para-tartaric acid was found to exhibit chiral asymmetry, with different enantiomers of this molecule shown to be able to distinguish differently polarized light. The next significant breakthrough was the discovery of liquid crystals, which opened up the era of liquid crystal displays based largely on nematic liquid crystals, though the seminal work was on their chiral nematic (cholesteric) cousins Chiral properties were later discovered in biology and physics, such as the DNA double-helix and parity non-conservation phenomena, respectively. In material science, three categories of chiral materials were introduced sequentially, namely organic chiral materials, inorganic chiral materials, and hybrid organic-inorganic chiral materials. Among those, the chiral organic-inorganic metal halide perovskites are considered in detail in this thesis.
The parameters and the characteristics of chiral properties and the corresponding applications are introduced in Chapter 2. The fundamental concept of light polarization is explained based on the concepts of linear polarization and circular polarization including right- and left-hand circularly polarized light. Circular dichroism is one of the key features of chiral materials, which reflects the absorbance difference when they are illuminated by left- and then right-handed circularly polarized light. The basic definition of circular dichroism and the principle of circular dichroism measurements using various approaches are considered. Another vital feature of chiral materials is their circularly polarized luminescence, which is elucidated according to the fundamental definition and theories, along with the corresponding experimental methodologies. In addition, chiral materials can also manifest chiral-induced spin selectivity, non-linear chiroptical effects, and ferroelectric properties and these are illustrated in this chapter accordingly. Moreover, two important application configurations, photodetectors and field effect transistors (FETs) are introduced based on their working principles and parameter analysis, followed by the related experiment studies of such devices based on chiral organic-inorganic halide perovskites, which can form the basis for direct circularly polarized photodetectors, light-emitting diodes, spin photogalvanic, and spintronic devices.
The following three chapters (Chapter 3-5) present three experimental studies conducted within this thesis. In Chapter 3, organic-inorganic (hybrid) metal halide perovskites (MHPs) incorporating chiral organic ligand molecules are shown to be naturally sensitive to left- and right-handed circular polarized light, potentially enabling selective circular polarized photodetection. The photoresponses in chiral MHP polycrystalline thin films made of ((S)-(−)-α-methyl benzylamine)2PbI4 and ((R)-(+)-α-methyl benzylamine)2PbI4, denoted as (S-MBA)2PbI4 and (R-MBA)2PbI4, respectively, are investigated by employing a thin-film field-effect transistor (FET) configuration. The left-hand-sensitive films made of (S-MBA)2PbI4 perovskite show higher photocurrent under left-handed circularly polarized (LCP) light than under right-handed circularly polarized (RCP) illumination under otherwise identical conditions. Conversely, the right-hand-sensitive films made of (R-MBA)2PbI4 are more sensitive to RCP than LCP illumination over a wide temperature range of 77–300 K. Furthermore, based on FET measurements, we found evidence of two different carrier transport mechanisms with two distinct activation energies in the 77–260 K and 280–300 K temperature ranges, respectively. In the former temperature range, shallow traps are dominant in the perovskite film, which is filled by thermally activated carriers with increasing temperature; in the latter temperature range, deep traps with one order of magnitude larger activation energy dominate. Both types of chiral MHPs show intrinsic p-type carrier transport behavior regardless of the handedness (S or R) of these materials. The optimal carrier mobility for both handedness of this material is found to be around (2.7 ± 0.2) × 10–7 cm2 V–1 s–1 at 270–280 K, which is two magnitudes larger than those reported previously for nonchiral perovskite MAPbI3 polycrystalline thin films. These findings suggest that chiral MHPs can be an excellent candidate for selective circular polarized photodetection applications, without additional polarizing optical components, enabling simplified construction of detection systems.
In Chapter 4, thin-film FETs based on chiral quasi-two-dimensional hybrid perovskites are explored, and the temperature dependence of the charge carrier transport mechanism over a broad temperature range (80–300 K) is revealed. A typical p-type charge transport behavior is observed for both left-handed (S-C6H5(CN2)2NH3)2(CH3NH3)n−1PbnI3n+1 and right-handed (R-C6H5(CN2)2NH3)2(CH3NH3)n−1PbnI3n+1 chiral perovskites, with maximum carrier mobilities of 1.7 × 10–5 cm2 V–1 s–1 and 2.5 × 10–5 cm2 V–1 s–1 at around 280 K, respectively. The shallow traps with smaller activation energy (0.03 eV) hinder the carrier transport over the lower temperature regime (80–180 K), while deep traps with one order of magnitude larger activation energy than the shallow traps moderate the charge carrier transport in the temperature range of 180–300 K. From the charge carrier mechanism point of view, impurity scattering is established as the dominant factor from 80 K until around 280 K, while in contrast, phonon scattering becomes predominant up to room temperature. Responsivities of 0.15 A W–1 and 0.14 A W–1 for left-handed and right-handed chiral perovskite FET devices are obtained.
In Chapter 5, yet another type of chiral (non-perovskite) material based on AgBiS2 nanocrystals is explored. Based on the developed chiral ligand exchange performed on AgBiS2 nanocrystals post-synthetically, a strong, long-lasting CD signal in the near-UV region is demonstrated. By carefully optimizing the ligand concentration, peak CD effects are observed at 260 and 320 nm, respectively, giving insight into the different ligand binding mechanisms influencing the CD signal in AgBiS2. The corresponding FET device performance of devices constructed with these materials illustrates the typical p-type carrier transport with 1.3× 10–3 cm2 V–1 s–1 for L-Cysteine treated AgBiS2 nanocrystals. This study represents a considerable advancement in the field of chiral nanocrystals and points toward their future applications.
Overall, this thesis provides several meaningful research studies of chiral perovskites and chiral AgBiS2 nanocrystals by illustrating their capability for use in direct circularly polarized photodetection and showing relevant FET performance to explore the underlying chiral charge carrier transport for a better understanding of the carrier transport mechanisms, which can be exploited to improve the device performance.
