Ultranarrow‐Spaced Polar Green Aromatic Dion–Jacobson Hybrid Perovskite Enables Highly Sensitive and Stable Self‐Powered X‐Ray Detection

ABSTRACT

Dion‐Jacobson (DJ) hybrid perovskites are considered as highly promising X‐ray detection materials due to their high stability and short interlayer spacing. However, the large‐scale commercial development of these materials is challenged due to severe ion migration at high voltage and lead toxicity. Here, we successfully obtained a DJ‐type polar lead‐free green hybrid perovskite (4AMPY)₂AgBiBr₈ (1) by inserting 4‐aminomethylpyridine (4AMPY) aromatic diamine into 3D Cs₂AgBiBr₆, and achieved efficient and stable self‐powered X‐ray detection. Specifically, owing to the insertion of 4AMPY, 1 crystallizes in polar space group P2₁ and exhibits a significant bulk photovoltaic effect. Additionally, strong hydrogen‐bonding interactions between 4AMPY and adjacent inorganic layers lead to an ultranarrow interlayer spacing of 3.09 Å. Meanwhile, the enhanced electron cloud density in aromatic diamines improves the charge transfer channel of 1 and enhances its X‐ray detection performance. Therefore, among all DJ‐type lead‐free hybrid perovskites, 1 achieves record‐breaking sensitivities of 661.4 and 9465.2 µC Gy⁻¹ cm⁻² at 0 and 100 V, respectively. Importantly, 1 exhibits excellent storage stability, with its sensitivity remaining at 97.5% (0 V) and 96.6% (100 V) of the initial value after three months. This work will greatly promote the development of polar DJ‐type lead‐free perovskite‐based self‐powered X‐ray detectors.

By inserting 4AMPY aromatic diamine into Cs₂AgBiBr₆, we successfully obtained a polar green DJ perovskite, (4AMPY)₂AgBiBr₈ (1), with an ultra‐narrow interlayer spacing of 3.09 Å. Benefiting from its significant BPVE, 1 achieves stable self‐powered X‐ray detection, including a record‐breaking sensitivity of 661.4 µC Gy⁻¹ cm⁻² and LoD of 12.3 nGy s⁻¹.

1. Introduction

Spontaneous polarization, as an intrinsic property of polar crystalline materials, is the physical origin of the built‐in electric field. Its generation is due to the non‐coincidence of positive and negative charge centers within the unit cell, which leads to the formation of macroscopic electric dipole moments and ultimately forms a stable built‐in electric field within the material [1, 2, 3]. When light with photon energy higher than the band gap illuminates such crystals, carriers undergo directional separation and transport driven by the built‐in electric field, with the direction consistent with the polarization orientation of the crystal. This phenomenon, where a steady‐state current is generated under illumination without the need for an external electric field, is known as the bulk photovoltaic effect (BPVE) [4, 5, 6]. Owing to these characteristics, polar materials demonstrate significant application potential in fields such as energy storage and conversion devices, pyroelectric sensors, and self‐powered X‐ray detection [7, 8]. For instance, Wang et al. utilized Bridgman crystal growth technology to obtain high‐quality LiGa_0.5In_0.5Se₂ with a giant BPVE, achieving highly efficient self‐powered X‐ray detection at 0 V bias [9]. However, the large‐scale application of such materials is greatly limited due to factors such as complex preparation processes, difficulties in crystal growth, and high costs. Although high‐performance self‐powered X‐ray detection can also be achieved through strategies such as constructing heterostructures, fabricating p‐i‐n‐type devices, and exploiting ferroelectrics [10, 11, 12] (Supporting Information, Table S1), the development of these detectors still faces significant obstacles, including cumbersome device fabrication processes and unclear design mechanisms of ferroelectricity. Therefore, it is urgent to develop new polar materials to overcome this problem.

In recent years, 2D hybrid perovskites (HPs) have shown strong carrier collection and transport efficiency, along with remarkable suppression of ion migration, due to the alternating arrangement of large organic amine components and inorganic frameworks within their structure. This makes them an ideal system for achieving high‐performance X‐ray detection [13, 14]. Particularly, the diamine spacers in Dion‐Jacobson (DJ)‐type HPs significantly reduce the distance between adjacent inorganic layers and eliminate van der Waals gaps. This short interlayer spacing facilitates the rapid separation and transport of photogenerated carriers, thereby enhancing the X‐ray detection performance of the devices. Additionally, the strong hydrogen bonding interactions formed between both ends of the diamine and the inorganic layers further greatly enhance structural stability [15, 16, 17]. Although some DJ‐type HP X‐ray detectors have been developed, such as (DGA)PbI₄ (DGA = 1, 1‐dimethylbiguanide) [18], (4AMP)Cs₂Pb₃Br₁₀ (4AMP = 4‐ammoniomethylpiperidinium) [8], and (DPA)PbBr₄ (DPA = NH₃C₅H₁₀NH₃) [19], the toxicity of Pb‐based materials poses serious threats to human health and the environment. Meanwhile, the above‐mentioned X‐ray detectors are based on aliphatic amine HPs with lower dielectric constants and lower charge transport capabilities [20, 21]. Aromatic diamines with high dielectric constants can increase electron cloud density and enhance electron‐phonon coupling between adjacent inorganic layers, while mitigating dielectric confinement effect [22, 23]. These effects collectively promote interlayer charge transport efficiency and detection sensitivity. Unfortunately, the strong rigidity of aromatic organic diamines makes the hybrid perovskite materials constructed from them more prone to forming 1D and 0D structures [24, 25, 26]. This results in the continued rarity of DJ‐type HPs, let alone lead‐free polar DJ‐type HPs capable of self‐powered X‐ray detection. Despite significant efforts by many researchers in this field, developing high‐performance and highly stable DJ‐type lead‐free HP self‐powered X‐ray detectors remains highly challenging.

To overcome these challenges, we developed an aromatic‐type DJ polar lead‐free “green” HP (4AMPY)₂AgBiBr₈ (1, 4AMPY = 4‐aminomethylpyridine), which enables efficient and stable self‐powered X‐ray detection. Specifically, we induced the reconstruction of the classical 3D HP Cs₂AgBiBr₆ into a 2D DJ‐type HP by the strategic insertion of the 4AMPY aromatic organic diamine (Scheme 1). Especially, due to the insertion of organic components of 4AMPY, 1 crystallizes in the polar space group P2₁ and exhibits a significant BPVE. Its photovoltage under X‐ray irradiation reaches 0.68 V, which is used as a driving force for carrier separation and transport in efficient self‐powered X‐ray detection. In addition, the 4AMPY organic diamine cation is connected to the inorganic layer through strong hydrogen bonds, resulting in a layer spacing of only 3.09 Å, which is very conducive to the rapid separation and transport of photogenerated carriers between layers, thereby achieving efficient X‐ray detection. Consequently, in self‐powered mode and under a 100 V bias, compound 1 achieves record‐breaking sensitivities of 661.4 and 9645.2 µC Gy⁻¹ cm⁻², respectively, among DJ‐type lead‐free HP single‐crystal X‐ray detectors. Notably, 1 also exhibits an ultra‐low detection limit of 12.3 nGy s⁻¹, far lower than many similar detection materials and traditional inorganic semiconductor materials. Furthermore, the strong hydrogen bonding forces within the structure endow it with significant stability, including a low dark current drift value of 5.3 × 10⁻⁷ nA cm⁻¹ s⁻¹ under 100 V bias and exceptional radiation stability (withstanding up to 2.39 Gy) and long‐term storage stability. After three months without any packaging, 1 retained 97.5% and 96.6% of its initial sensitivity at 0 and 100 V bias, respectively. This work provides a new insight for the further development of highly stable DJ‐type lead‐free HPs self‐powered X‐ray detectors.

SCHEME 1.

Inserting a 4AMPY aromatic organic diamine cation into 3D centrosymmetric HP Cs₂AgBiBr₆ to construct 2D polar green aromatic DJ‐type HP (4AMPY)₂AgBiBr₈.

2. Results and Discussion

Bulk single crystals of 1 were grown from a saturated hydrobromic acid solution using a slow cooling method (Figure 1a; for specific details, please refer to Section S1 the experimental synthesis and growth section in the Supporting Information). The structure of 1 was collected and analyzed using an X‐ray single‐crystal diffractometer. The results show that 1 crystallizes in the polar space group P2₁, and more detailed crystallographic information is shown in Tables S2–S4. It should first be noted that the aromatic diamine cation containing 4‐aminomethylpyridine used in this work was rationally selected based on the structural design principles of Dion–Jacobson perovskites, rather than through high‐throughput screening (more detailed explanations can be found in the “Material Design Rationale” section of the Supporting Information). Additionally, the X‐ray powder diffraction pattern confirmed the phase purity of 1 (Figure S1). Structural analysis shows that it has a typical DJ‐type 2D quantum well structure. Among them, the AgBr₆ and BiBr₆ octahedral inorganic frameworks are alternately connected via corner‐sharing, collectively forming an inorganic layered structure. The 4AMPY cation acts as an organic barrier and is orderly distributed between adjacent inorganic layers (Figures S2 and S3). Meanwhile, the observed average Ag─Br─Bi bond angle of 167.4° indicates that the inorganic skeleton has undergone distortion (Figure S4). The degree of distortion of its inorganic skeleton layer can also be evaluated by the deviation of the Ag─Br and Bi─Br bond lengths of AgBr₆ and BiBr₆ octahedra. The deformation index (D) and bond angle variance (𝜎²) can be calculated using this equation to obtain [27]:

$$D=\left(\frac{1}{6}\right)\sum _{i=1}^6\left(\frac{d_i-d}{d}\right)$$

$${\sigma }^2=\sum _{i=1}^{12}\frac{{\left({\theta }_i-90\right)}^2}{11}$$

Where d_i is the bond length of Ag─Br and Bi─Br, and the d is the average length of all Ag─Br and Bi─Br bonds in the AgBr₆ and BiBr₆ octahedra; θ _i represents the bond angle of the Ag─Br/Bi─Br bond. The calculated D values for AgBr₆ and BiBr₆ were determined to be 0.049 and 0.019, respectively, with an 𝜎² value of 2.73 deg². Collectively, the inorganic layer in crystal 1 has undergone a small degree of structural distortion. This more regular inorganic framework facilitates electron cloud aggregation and the formation of well‐defined carrier transport channels, thereby enhancing charge transfer efficiency [28, 29]. As shown in Figure 1b, 4AMPY organic diamine can also form strong N‐H···Br hydrogen bonding forces at both ends to connect with adjacent inorganic frameworks. Moreover, the Hirshfeld surface analysis of 4AMPY confirms the presence of C‐H···Br hydrogen bonding forces in the structure (Figure 1c). Further visualization analysis was conducted on the strength of hydrogen bonding forces using the corresponding 2D fingerprint spectra of 4AMPY organic components. As shown in Figure 1d and Figure S5, the N─H···Br and C─H···Br hydrogen bonds account for 62.8% and 7.1% of the total surface area, respectively, which is much higher than RP‐type HPs such as (4FPEA)₂PbI₄ (31.1%, FPEA = 4‐fluorophenethylammonium) [30] and (PMA)₂PbI₄ (34.3%) [31]. These strong hydrogen‐bonding forces can eliminate interlayer van der Waals interactions and significantly enhance structural stability and lattice rigidity, thus facilitating their application in complex environments. It is worth noting that the DJ‐type structure constructed by 4AMPY organic diamine also endows it with an ultra‐short interlayer spacing of 3.09 Å (Figure 1e). This value is much lower than other HP materials of the same type, such as (FPEA)₄AgBiBr₈ [32], (HA)₄AgBiBr₈ (HA = histammonium) [33], and (PA)₄AgBiBr₈ (PA = propylammonium) [34] (Figure 1f). Excitingly, this value is currently the smallest among materials of the same type, except for (4AP)₂AgBiBr₈ (4AP = 4‐amidinopyridine) [35]. This shorter interlayer spacing is beneficial for promoting the separation and transmission efficiency of photo‐generated carriers, thereby effectively improving the X‐ray detection sensitivity of the crystal. Additionally, the density of 1 up to 3.02 g cm⁻³ enables it to efficiently absorb X‐rays, which is the basis for achieving high‐performance X‐ray detection [36, 37]. Therefore, 1 is a highly promising and efficient self‐powered X‐ray detection material.

FIGURE 1.

(a) High‐quality large crystal photo of 1. (b) Analysis diagram of strong hydrogen bonding forces in the structure. (c) Hirshfeld surface analyses of the 4AMPY²⁺ cations, and the light red dots represent N‐H···Br and C‐H···Br hydrogen bonds. (d) The corresponding 2D fingerprint plots analyzed. (e) The interlayer distance of 1. (f) Comparison of interlayer distance and density with other double perovskites. FPEA, R‐MPA, CPA, PA, DFPD, HA, BDA represent (FPEA)₄AgBiBr₈ [32], (R‐MPA)₄AgBiI₈ (R‐MPA = R‐β‐methylphenethylammonium) [38], (CPA)₄AgBiBr₈ (CPA = chloropropylammonium) [39], (PA)₄AgBiBr₈ [34], (DFPD)₄AgBiI₈ (DFPD = 4,4‐difluoropiperidinium) [40], (HA)₄AgBiBr₈ [33], (BDA)₄AgBiBr₈ (BDA = 1, 4‐butanediamine) [41].

Further measurements and analysis were conducted on its phase optics and semiconductor properties to better predict its photoelectric detection potential. For single‐crystal materials with high transparency, using transmission geometry to measure the optical absorption of the single crystal is more appropriate for evaluating the optical bandgap than using diffuse reflectance spectroscopy on powder samples combined with the Kubelka–Munk transformation. Therefore, we selected a single crystal with a thickness of 126.124 µm for transmission measurement, calculated its absorption coefficients as a function of wavelength, and obtained an optical bandgap of 2.39 eV. (Figure 2a; Figure S6) [42] Furthermore, the electronic structure and characteristics of compound 1 were theoretically calculated using density functional theory (DFT). The calculation results reveal that the bandgap of compound 1 is 2.63 eV, and its conduction band minimum (CBM) and valence band maximum (VBM) are located at the same k‐point in the Brillouin zone, indicating that it is a direct bandgap semiconductor (Figure 2b). Further calculations show that the contribution to the CBM mainly originates from the C 2p and N 2p orbitals, while the contribution to the VBM mainly originates from the Br 4p and Ag 4d orbitals (Figures S7 and S8). It should be explained that 2D hybrid perovskite materials typically possess strong exciton effects, which can result in the single‐particle electronic bandgap obtained from DFT calculations (2.63 eV) being larger than the optical bandgap (2.39 eV). Therefore, we further verified the exciton effects through temperature‐dependent photoluminescence spectroscopy [43]. The calculated exciton binding energy of crystal 1 is as high as 213.10 meV (Figure S9). This confirms that the optical bandgap being lower than the calculated value is mainly due to the intrinsic exciton binding in the material (please refer to Figure S9 for a more detailed explanation). In addition, 1 also has a high resistivity (ρ) of 8.64 × 10¹⁰ Ω cm, which is much higher than HP materials such as (I‐BA)₄AgBiI₈ (3.04 × 10¹⁰ Ω cm, I‐BA = I‐n‐butylammonium) [44], (S‐PPA)₄(IPA)₆Ag₂Bi₄I₂₄·2H₂O, (3.36×10⁹ Ω cm, S‐PPA = S‐1‐phenylpropylamine, IPA = isopentylamine) [45] and (PA)₄AgBiBr₈, (1.5 × 10⁹ Ω cm) [34] (Figure 2c). The high resistivity characteristic of the material is beneficial for suppressing current noise and improving the detection limit [18]. High‐quality crystals are a prerequisite for achieving excellent X‐ray detection performance. Therefore, an X‐ray detector with a typical metal–semiconductor–metal (MSM) structure (Ag/single‐crystal/Ag) was constructed based on a high‐quality single crystal of 1, and the space‐charge‐limited current (SCLC) method was used to evaluate the internal defects of the crystal (Figure S10) [30]. According to the rate of current increase, the voltage can be divided into three parts: Ohmic region, trap‐filled limited region, and Child region. As shown in Figure 2d, the magnitude of dark current increases continuously with the continuous rise of voltage, and shows a sharp increase trend after passing through a voltage of 9 V (V _TFL). The charge‐trap density can be calculated using the following formula [46]:

$$n_{\mathrm{trap}}=\frac{2\epsilon {\epsilon }_0{V}_{\mathrm{TFL}}}{\mathrm{e}{L}^2}$$

where ε, ε ₀, e, and L are the vacuum dielectric constant, dielectric constant, fundamental charge, and the sample thickness, respectively. Therefore, the calculated n _trap value is 1.17 × 10¹⁰ cm⁻³, much lower than that of classic 3D HP materials such as FAPbI₃ (2.6 × 10¹² cm⁻³) [47], MAPbBr₃ (2.8 × 10¹² cm⁻³) [48]. Furthermore, the surface morphology was analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). As shown in Figure 2e,f, the surface of the crystal is smooth and flat without obvious defects. These results confirm that 1 has high quality and is expected to achieve high‐performance self‐powered X‐ray detection.

FIGURE 2.

(a) The absorption coefficient of crystal 1 at different wavelengths and the calculated optical band gap (inset). (b) The density functional theory (DFT) calculations of 1. (c) The resistivity of 1. (d) The defect density of 1 was measured by the SCLC method. (e, f) SEM and AFM images of 1.

The excellent X‐ray absorption capability is essential for achieving efficient X‐ray detection. Therefore, the X‐ray absorption and attenuation coefficients of 1 were calculated using the photon cross‐section database [49]. As shown in Figure 3a,b, 1 exhibits exceptional X‐ray absorption coefficient and attenuation coefficient due to its composition of high‐atomic‐number elements such as bismuth (Bi) and bromine (Br) [50]. Moreover, 1 not only outperforms similar (HIS)₂AgSbBr₈ hybrid perovskite materials, but also significantly surpasses conventional silicon‐based inorganic semiconductor materials [8]. Notably, the atomic number of the metal Bi (83) is significantly higher than that of Sb (51), resulting in X‐ray absorption and attenuation properties of Bi‐based hybrid perovskites that are far superior to those of their Sb‐based counterparts. Therefore, 1 holds promise as a potential candidate for achieving high‐performance X‐ray detection. Subsequently, the charge collection capability of an X‐ray detector constructed using 1 was further evaluated, with its performance quantified by the carrier mobility‐lifetime product (µτ) value. The calculation formula is as follows [51]:

$$I=\frac{I_0\mu \tau V}{L^2}\left[1-\exp \left(\frac{-L^2}{\mu \tau V}\right)\right]$$

In the equation, I₀ , V, and L represent the saturation photocurrent, external bias voltage, and device thickness, respectively. Therefore, the calculated µτ value for 1 is 3.88 × 10⁻⁴ cm² V⁻¹, which is higher than that of HPs materials such as (4FPEA)₄AgBiBr₈ (2.9 × 10⁻⁵ cm² V⁻¹) [32], (R‐MPA)₄AgBiI₈ (2.2 × 10⁻⁵ cm² V⁻¹) [38], and (BZA)₃BiI₆ (5.94 × 10⁻⁵ cm² V⁻¹, BZA = benzylamine) [52]. Concurrently, the BPVE in 1 was verified by evaluating its second‐harmonic generation (SHG) intensity and measuring the resulting photocurrent under different X‐ray doses. As shown in Figure S11, 1 exhibits a strong SHG signal, with an intensity about 0.61 times that of potassium dihydrogen phosphate (KDP), further confirming its non‐centrosymmetric structure. As anticipated, the device exhibited a significant photovoltage of 0.68 V under illumination, comparable to other reported HP materials such as (3MePO)PbBr₄ (0.45 V, 3MePO = 3‐methylaminopropylamine) [53], MhyPbBr₃ (0.47 V, Mhy = methylhydrazine) [54]. (Figure 3d) Based on this, we conducted a detailed investigation of its X‐ray detection performance. As shown in Figure 3e, the device's response at 0 V bias increased with rising X‐ray irradiation dose, demonstrating an exciting self‐powered detection response. Furthermore, the response intensity of device 1 increased significantly at bias voltages of 10, 30, 50, 80, and 100 V, showing a positive correlation with the applied voltage. (Figure S12; Figure 3f). This enhancement is primarily attributed to 1’s exceptional charge collection capability. These results further demonstrate 1’s potential as a highly promising, high‐performance X‐ray detection material.

FIGURE 3.

(a) The absorption spectra of 1, Si, α‐Se, (HIS)₂AgSbBr₈, and (HIS)₂AgBiBr₈. (b) Attenuation efficiency of 50 keV X‐ray photons under different thicknesses for 1, Si, α‐Se, (HIS)₂AgSbBr_8, and (HIS)₂AgBiBr₈. (c) The 𝜇𝜏 product values of 1. (d) Photovoltage of device 1 measured under different X‐ray irradiation doses. (e, f) The X‐ray response intensity of device 1 under 0 V bias and 100 V bias. (g) The dependence of the response intensity of device 1 on dose rate under different biases. (h) The sensitivity of device 1 obtained by fitting under different biases. (i) Detection limit of device 1 under 0 V bias.

Sensitivity serves as a crucial metric for evaluating device performance. As shown in Figure 3g, this value can be obtained by fitting the photo‐response current density (photo‐current density minus dark current density: J _photo–J _dark) under different X‐ray radiation dose rates (D _x‐ray). The specific calculation method is as follows [51]:

$$S=\frac{\left(J_{photo}-J_{dark}\right)}{D_{x-ray}}$$

Therefore, calculations yielded the sensitivities at 0, 10, 30, 50, 80, and 100 V as 661.4, 3194.1, 5427.4, 6793.9, 7654.0, and 9645.2 µC Gy⁻¹ cm⁻², respectively (Figure 3h). Excitingly, the device exhibits higher sensitivity in self‐powered mode than many HP materials, such as (iPA)₂PbBr₄ (51.4 µC Gy⁻¹ cm⁻², iPA = isopropylammonium) [55], (3AP)PbI₄ (124.8 µC Gy⁻¹ cm⁻², 5 V, 3AP = 3‐amidinopyridine) [56] and (BA)₂PbI₄ (148 µC Gy⁻¹ cm⁻², 10 V mm⁻¹) [14]. Additionally, low detection limits hold significant importance in the practical application of devices. Particularly in the field of clinical medicine, achieving low detection limits in X‐ray detection can minimize the damage caused by X‐ray radiation to the human body. The International Union of Pure and Applied Chemistry (IUPAC) defines the detection limit of an X‐ray detector as the dose rate corresponding to a signal‐to‐noise ratio of 3. Its magnitude can be calculated using the following equation [37]:

$$SNR=\frac{\overline{I_{\mathrm{photo}}}-\overline{I_{\mathrm{dark}}}}{\sqrt{\frac{1}{N}{\sum }_i^n{\left(I_i-\overline{I_{\mathrm{photo}}}\right)}^2}}$$

In the equation, $\overline{I_{\mathrm{photo}}}$, $\overline{I_{\mathrm{dark}}}$ and I_i represent the average photocurrent, average dark current, and measured photocurrent, respectively. As shown in Figure 3i, the device achieves a detection limit as low as 12.3 nGy s⁻¹ in self‐powered mode, significantly surpassing that of commercial α‐Se detectors (5500 nGy s⁻¹) [57]. This is because the device is unaffected by high‐current noise induced by external bias, enabling a low detection limit in self‐powered mode [37]. Excitingly, even under different bias voltages such as 10, 30, 50, and 80 V, the device exhibits an ultra‐low detection limit, with the maximum value being only 28.1 nGy s⁻¹ (Figure S13). Besides, it can be confirmed from Table S5 that device 1 exhibits highly advanced X‐ray detection sensitivity and detection limit among similar HP materials. Consequently, this device holds great promise for commercial applications in fields such as clinical medicine. In the context of the aforementioned characteristics, the stability of the device significantly impacts its scope of practical application. As shown in Figure S14, crystal 1 exhibits a high onset decomposition temperature of approximately 574 K, significantly surpassing that of many analogous HPs such as (4AP)₂AgBiBr₈ (528 K) [35], (DFPD)₄AgBiI₈ (506 K) [40], and (I‐BA)₄AgBiI₈ (460 K) [43]. To verify the storage stability of 1, we characterized its phase purity at one‐month and three‐month intervals (Figure 4a). The results show that there have been no significant changes to the crystal's phase, which demonstrates its excellent storage stability. Furthermore, the device's ability to suppress ion migration was evaluated, and this can be analyzed through the magnitude of dark current drift (I _drift). As shown in Figure 4b,c and Table S6, the I _drift under a high bias voltage of 100 V was only 5.3 × 10⁻⁷ nA cm⁻¹ s⁻¹ V⁻¹ (initial) and 9.9 × 10⁻⁷ nA cm⁻¹ s⁻¹ V⁻¹ (3 months later), significantly lower than other HPs materials such as (DGA)PbI₄ (5.97 × 10⁻⁷ nA cm⁻¹ s⁻¹ V⁻¹ under 10 V) [21], (BDA)(MA)₂Pb₃Br₁₀ (2.97 × 10⁻⁵ nA cm⁻¹ s⁻¹ V⁻¹ under 11.1 V mm⁻¹) [58] and (R‐PPA)₂BiI₅ (1.0 × 10⁻⁴ nA cm⁻¹ s⁻¹ V⁻¹ under 10 V) [37]. Additionally, we also measured the ion migration activation energy (E _a) of the device to further confirm its excellent ability to suppress ion migration. As shown in Figure S15 and Table S7, the results indicate that the ion migration activation energy of device 1 is as high as 0.87 eV, which is much higher than that of many reported hybrid perovskite materials. These results strongly confirm that device 1 can suppress ion migration and prolong its own lifespan. Then, after three months without encapsulation, we tested the X‐ray detection performance of device 1 in self‐powered mode and under 100 V bias (Figure 4d,e; Figure S16). These results confirmed that device 1 maintains an excellent X‐ray response, with a sensitivity retention of 97.5% in self‐powered mode and 96.6% under 100 V bias, respectively. Furthermore, the device exhibited only a marginal increase in its detection limit, highlighting its stability (Figure 4f; Figure S17). Finally, we tested the radiation stability of the device under high X‐ray irradiation doses of 159.8 and 1749 µGy s⁻¹ (Figure 4g). Device 1 not only maintains a stable on/off switching response under different high‐dose irradiation, but also exhibits highly stable light response intensity after receiving approximately 2.39 Gy of X‐ray irradiation. Especially, even after three months, device 1 maintained excellent radiation stability with only a slight decrease in response intensity. Collectively, these results demonstrate that X‐ray detectors based on crystal 1 possess outstanding detection performance and high stability.

FIGURE 4.

(a) PXRD patterns of 1 after being left unpackaged for 1 and 3 months, respectively. (b) The initial I _drift value of sample 1 and the value after being left unpackaged for 3 months. (c) The I _drift values of device 1 compared with other HP materials. (d) Compare the X‐ray response of device 1 with the initial value after three months. (e) Compare the detection sensitivity of device 1 with the initial value after three months. (f) Compare the detection limit of device 1 with the initial value after three months. (g) The radiation resistance stability of device 1.

3. Conclusions

In summary, by inserting the large‐sized aromatic diamine cationic spacer 4AMPY into the 3D HP Cs₂AgBiBr₆, we successfully obtained a DJ‐type polar lead‐free HP (4AMPY)₂AgBiBr₈ (1) and achieved highly efficient and stable X‐ray detection. In particular, the spontaneous polarization effect endowed by its polarity characteristics enables crystal materials to achieve the potential for self‐powered X‐ray detection with the ability to suppress ion migration. In addition, the ultra‐narrow interlayer spacing and aromatic diamine in the DJ‐type perovskite structure not only promote the charge collection and carrier transport efficiency of the material, but also further enhance the stability of the material through the strong hydrogen bonding force formed between the diamine cation and adjacent inorganic frameworks. Therefore, based on these foundations, the device ultimately achieved high‐performance self‐powered X‐ray detection, including a record‐breaking sensitivity of 661.4 µC Gy⁻¹ cm⁻² and an ultralow detection limit of 12.3 nGy s⁻¹. Importantly, the single‐crystal X‐ray detection device of 1 also exhibits excellent stability, including resistance to high‐dose radiation and long‐term storage stability. Therefore, our work not only develops a stable and efficient HP single‐crystal self‐powered X‐ray detection material, but also will strongly promote the rapid development of such materials.

Author Contributions

H.Y. and L.Z. prepared single crystals and tested the X‐ray detection performance. H.Y. and Z.‐K.Z. wrote and revised this manuscript. L.Z. and H.G. fabricated single‐crystal devices and analyzed the X‐ray detection performance data. J.W. and Y.W. calculated the semiconductor and optical properties of the crystal. W.W. and P.Y. conducted research and summarized relevant literature. Y.Z. and H.‐P.X. tested the crystal morphology characteristics. Z.‐K.Z. and J.L. provided research ideas and guided the completion of the manuscript. All authors have contributed to the review of this manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Supporting File: adma73657‐sup‐0001‐SuppMat.docx.

Data Availability Statement

CCDC 2511987 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.