Sajjad
Hussain‡
ab,
Hailiang
Liu‡
c,
Dhanasekaran
Vikraman
d,
Syed Hassan Abbas
Jaffery
ab,
Ghazanfar
Nazir
b,
Faisal
Shahzad
e,
Khalid Mujasam
Batoo
f,
Jongwan
Jung
ab,
Jungwon
Kang
*c and
Hyun-Seok
Kim
*d
aHybrid Materials Center (HMC), Sejong University, Seoul 05006, Korea
bDepartment of Nanotechnology and Advanced Materials Engineering, Sejong University, Seoul 05006, Korea
cConvergence Semiconductor Research Center, Department of Electronics and Electrical Engineering, Dankook University, Yongin 16890, Korea. E-mail: jkang@dankook.ac.kr
dDivision of Electronics and Electrical Engineering, Dongguk University-Seoul, Seoul 04620, Korea. E-mail: hyunseokk@dongguk.edu
eDepartment of Metallurgy and Materials Engineering, Pakistan Institute of Engineering and Applied Sciences (PIEAS), Islamabad, Pakistan
fKing Abdullah Institute for Nanotechnology, King Saud University, Riyadh-11451, Saudi Arabia
First published on 16th March 2023
This work elaborates on the decoration of metal oxides (ZnO and Fe3O4) between MXene sheets for use as the supporting geometry of PCBM electron transport layers (ETLs) in perovskite solar cells and X-ray detectors. The metal oxide supports for carrying the plentiful charge carriers and the hydrophobic nature of MXenes provide an easy charge transfer path through their flakes and a smooth surface for the ETL. The developed interface engineering based on the MXene/ZnO and MXene/Fe3O4 hybrid ETL results in improved power conversion efficiencies (PCEs) of 13.31% and 13.79%, respectively. The observed PCE is improved to 25.80% and 30.34% by blending the MXene/ZnO and MXene/Fe3O4 nanoparticles with the PCBM layer, respectively. Various factors, such as surface modification, swift interfacial interaction, roughness decrement, and charge transport improvement, are strongly influenced to improve the device performance. Moreover, X-ray detectors with the MXene/Fe3O4-modulated PCBM ETL achieve a CCD-DCD, sensitivity, mobility, and trap density of 15.46 μA cm−2, 4.63 mA per Gy per cm2, 5.21 × 10−4 cm2 V−1 s−1, and 1.47 × 1015 cm2 V−1 s−1, respectively. Metal oxide-decorated MXene sheets incorporating the PCBM ETL are a significant route for improving the photoactive species generation, long-term stability, and high mobility of perovskite-based devices.
In typical perovskite-based devices, a planar perovskite layer is embedded between a hole transfer layer (HTL) and an electron transfer layer (ETL) (ITO/HTL/perovskite layer/ETL/Au, Ag, or Al) in a gadget module to attract photon light and create electron–hole charge carriers. The transport layer(s) (HTL and ETL) and active perovskite layer play significant roles in improving the cell efficiency and stability. Moreover, the ETL is a vital layer in perovskite devices for charge transport, collection and extraction, eradicating electrical shunts between the perovskite and transparent electrode, and facilitating the trapping and recombination of charge carriers. The fullerene derivative, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), is the most conventional ETL for transporting electrons and effectively passivating any defects in the perovskite layer. However, there are many limitations to using the conventional PCBM ETL when fabricating perovskite devices. First, the uniformity of a PCBM ETL depends on the morphology beneath the perovskite active layer due to the larger size grain and rough or uneven nature of perovskites, which leave an opening or void. Second, during metal electrode deposition, hot metals permeate into them to develop direct interaction with the active layer perovskite, resulting to the neutralizing of excitons. Third, very thick PCBM ETLs produce a smooth surface that highly restrict the transportation and mobility (due to imbalanced light absorption efficiency) and scalable fabrication due to high cost.14 Finally, PCBM is a hygroscopic material that is severely affected by moisture, which can degrade the robustness of perovskite-based devices. Many significant approaches have been implemented to enhance the enactment of perovskite devices by replacing or altering the PCBM ETL. Recently, metal oxide (MO) semiconductors including TiO2, SnO2, Cr2O3, CeO2, Fe3O4, ZnO, Nb2O5, and Zn2SnO4 have been employed to replace or modify the PCBM layer.15–19 In particular, modifying, doping, or multi-layer configurations of the ETL layer using MO semiconductors reduces the morphological defects, improves uniform coverage and rapid charge transport ability, and eliminates hysteresis characteristics, creating favorable band alignment, excellent interface contact, and visible transparency.16,18,20
Among these semiconductors, ZnO and Fe3O4, which are n-type semiconductors with a wide bandgap (2–3.5 eV), are promising ETLs in perovskite devices owing to their intrinsic properties including a high electron transport rate of 130–230 cm2 V−1 s−1 and good chemical stability.21,22 Lim et al. demonstrated surface-modified ZnO ETLs on flexible substrates with an average power conversion efficiency (PCE) of 11.9%.23 Similarly, Hu et al. used hematite-based transportation films in perovskite-based solar cells that produced a PCE of 10.7%.24 However, there are some intrinsic drawbacks of ZnO and Fe3O4. These include poor conductivity and severe charge recombination centers that trap photogenerated electrons due to surface defects and the presence of metal (Zn or Fe) and oxygen vacancies, which severely hinder local charge transfer.25,26 Moreover, decomposition of the perovskite photoactive layer can easily corrode the Fe3O4 and ZnO ETL structures.27 To overcome these critical problems, several researchers have attempted to improve the conductivity of the MO ETL to suppress the recombination and trapping of charge carriers between the perovskite active and ETL interface by modifying or replacing the ETL through dopants or hybridization.
Two-dimensional (2D) MXene-based materials have received significant attention because of their distinctive properties. These include outstanding intrinsic ionic or electronic conductivity (5000–10000 S cm−1) close to that of multi-layered graphenes, hydrophilicity, ease of processing with rich surface chemistry, excellent optical transparency, existing in semimetals, superconductors or semiconductors (based on the surface characteristics), high carrier density (3.8 × 1022 cm−3), and superior mobility (1.0 cm2 V−1 s−1).28,29 Moreover, because of its charge carrier transference and gathering behaviors, MXenes have recently been used as both a HTL and an ETL to improve the efficiency and stability of PSCs.30,31 However, these materials are still in their infancy and limitedly used in HTLs to check the progress for the practical application. Highly conducting materials have been hybridized with MO and used as HTLs and ETLs such as perylene bisimide,32 nickel (Ni),33 aluminum (Al),34 and carbon-based derivatives (MXenes, graphenes, rGO, and CNTs).35 Recently, Jayawardena et al.36 and Hou et al.25 have incorporated ZnO with rGO and MXene-Ti3C2Tx to improve the PCE by providing charge extraction/collection channels between the ZnO nanoparticles. Mohammad et al.37 used the ZnO:CNT ETL to improve the crystallinity and charge transfer properties in the PSC. Tavakoli et al.38 employed a multilayer graphene interfacial layer to make smooth contact between ZnO and the perovskite layer and improve the thermal stability of PSCs, which realized a maximum PCE of 19.81%. Wang et al.39 have reported the use of MXene-modified SnO2 ETLs to realize an enhanced PCE of 20.65%.
From a detailed review of the literature, it is evident that MXene/MO is a suitable alternative supplement to include with the HTLs and ETLs to modify the photoactive layer morphology and promote intimate contact between the transport and photoactive layers, boosting perovskite device performance. Herein, we explore the effect of using MXene/ZnO and MXene/Fe3O4-embedded ETL perovskite devices for solar cells and X-ray detectors. The resulting solar cells composed of MXene/ZnO and MXene/Fe3O4 ETLs achieved PCEs of 13.31%, and 13.79%, respectively, which are superior to devices using pristine and ZnO- and Fe3O4-modified ETL outcomes. Moreover, X-ray detectors using MXene/ZnO and MXene/Fe3O4 hybrid composite ETL encompassed modules achieved a lower trap density and superior charge carrier transportation capabilities, resulting in high sensitivities of 4.41 and 4.63 mA per Gy per cm2, respectively. The metallic MXene nanosheets serve as bridges between MO nanocrystals and make connections that allow the flow of swift charge transfer paths. In addition, because of their high mobility and charge carrier density, the charge can easily travel through the MXene nanoflakes, reducing grain boundaries and discontinuities in the film and potentially extending the exciton's lifetime.
To ascertain the functional characteristics of the MXene/MO nanocomposites, Raman scattering analyses were performed on the prepared samples. Fig. 2b displays the Raman spectra of the MXene/ZnO and MXene/Fe3O4 nanocomposites. The characteristic MXene peaks explored at 204, 392, 619, and 722 cm−1 correlate with the results previously reported in the literature.42,44 Moreover, the Fe3O4 characteristic bands explore the A1g (220 cm−1), T2g (593 and 494 cm−1) and Eg (395 and 281 cm−1) phonon modes to reveal a strong Fe–O relationship in the MXene/Fe3O4 composites.45,46 The high-wavenumber Raman shift realized distinct Fe oxidation, as reported earlier.47,48 For the pure ZnO nanostructures, a dominant active mode at approximately 439 (E2H) was observed, due to the composing element of the wurtzite structure ZnO with good crystal quality.49,50 The peaks at approximately 336 and 586 cm−1 could be assigned to the Raman A1(TO) and E1(LO) mode, respectively.51,52 Moreover, two wide peaks were evident between 1100 and 1700 cm−1 due to the presence of disordered carbon (D) and graphitic carbon (G) peaks, which are credited to the sp2 sites.42,53 The exhibited ID/IG intensity ratios were 0.78 and 0.99 for MXene/Fe3O4 and MXene/ZnO, respectively. The enriched intensity of the G band revealed plentiful graphitic carbon, which can greatly enhance the charge transfer characteristic of the MXene layer, improving the device performance.
X-ray photoelectron spectroscopy (XPS) was performed to assess the elemental composition and oxidation states of the MXene/ZnO and MXene/Fe3O4 composites. Fig. 2c–f display the XPS profiles of the Ti 2p, C 1s, Zn 2p, and O 1s regions of the MXene/ZnO nanocomposites, respectively. The Ti 2p region (Fig. 2c) from the MXene/ZnO composite reveals the main characteristic peaks at 454.5 and 463.8 eV due to Ti–C and Ti3+, respectively, along with the representative Ti–O bonding peaks (458.7 and 460.6 eV).54 Moreover, the C 1s spectrum (Fig. 2d) of the MXene/ZnO composite establishes the Ti–C, C–C and CO peaks at 281.5, 284.5, and 288.7 eV, respectively. Fig. 2e defines the Zn 2p region of the MXene/ZnO nanocomposites, which establishes twins at 1021.75 and 1044.15 eV due to Zn 2p3/2 and 2p1/2, respectively. The observed oxidation state confirmed the existence of a Zn2+ valence band, which formed ZnO in the MXene/ZnO composites. For the O 1s region (Fig. 2f), the peaks at 532.1 and 531.4 eV contributed to the Zn–O and C–OH binding energies, respectively. For MXene/Fe3O4, the Ti 2p region (Fig. 2g) explores the Ti–C, Ti–O, and Ti3+ related peaks at 454.5, 459.9, and 463.3 eV, respectively. The C 1s region (Fig. 2h) gains the Ti–C, C–C, and CO binding energy peaks from the MXene of the MXene/Fe3O4 composites. Fig. 2i defines the Fe 2p binding energy region from the XPS profile, which confirmed the existence of Fe3+- and Fe2+-related 2p1/2 and 2p3/2 states along with the Fe satellite peak.43 The perceived outcomes strongly prove the existence of the multivalent state of Fe and bonding with MXene and O atoms in the composite structure.55,56 The O 1s deconvoluted profile explores at 529.3, 531.4, and 532.2 eV, which is allotted to CO, O–C–O, and Fe–O, respectively, as displayed in Fig. 2j.56 Fig. S2† displays XPS survey profiles of the MXene/ZnO and MXene/Fe3O4 composites.
The surface morphologies of the MXene/ZnO and MXene/Fe3O4 nanocomposites were characterized by field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). Fig. 3a–c display the FESEM images of the MXene/ZnO nanocomposites. The magnified images clearly demonstrate the decorated ZnO nanoparticles between the MXene nanosheets (Fig. 3(a and b). The insertion of nanoparticles fills the geometrical defects and creates smooth surface properties for the resulting devices. Moreover, high-resolution images demonstrate the interconnected ZnO nanostructures with uneven grain shapes due to the limited intersection between the nanoparticles. Elemental composition analyses of the prepared MXene/ZnO nanocomposites were also performed. Fig. S3a† displays the energy-dispersive spectral (EDS) profile of the MXene/ZnO composites. The observed results explore the 20, 12, 27, and 41 atomic percentages (at.%) of individual elements O, Zn, C, and Ti, respectively, in the MXene/ZnO composites (Fig. S3b†). Moreover, elemental mapping analyses were performed to visualize the dispersal of elements on the MXene/ZnO composite surface. Fig. S3c–g† clearly depict the identical dispersal of all the elements on the surface of the MXene/ZnO composites, while Fig. 3d displays the formation of arrangements of nanoparticles. The high-resolution images clearly depict defined ZnO nanograin intersections between the MXene sheets. Fig. 3f represents the protruding of ZnO structures on the MXene sheets. In addition, clear lattice fringes with distinct lattice directions (lattice planes are indicated with orange, yellow and white) of the array structure are visible in the high-resolution TEM image (Fig. 3g). Fig. 3h portrays the interfacing atomic arrangements with clear lattice fringes (lattice planes are indicated in yellow and red), while Fig. 3i displays the fast Fourier transform (FFT) pattern, which contains the crystalline pattern of Moire fringes.
Fig. 4a–c display the FESEM images of the MXene/Fe3O4 nanocomposites. The magnified image (Fig. 4a) depicts the decorated Fe3O4 nanoparticles between the MXene nanosheets and the edges of the sheets. The covering of Fe3O4 nanoparticles on the MXene sheets provides a protective layer, allowing the development of strong geometrical interactions and enriched surface properties. Moreover, the high-resolution image (Fig. 4c) demonstrates the strongly adhered MO particles between the MXenes. Fig. S4a† displays the EDS profile of the MXene/Fe3O4 composites. The observed results explore 24, 15, 23, and 38 at% of the individual elements O, Fe, C, and Ti, respectively, in the MXene/Fe3O4 composites (Fig. S4b†). Fig. S4c† confirms the elemental distribution of all the elements on the MXene/Fe3O4 composites. Fig. S4d–g† clearly depict the constant dispersal of Fe, O, Ti, and C elements, respectively, on the surface of MXene/Fe3O4 composites, while Fig. 4d depicts the development of nanosized grains. The high-resolution images (Fig. 4e and f) clearly display the different sizes of Fe3O4 nanograin intersections along the MXene sheets (lattice planes are indicated in different colors). Fig. 4g displays the high-resolution TEM image that indicates obvious lattice fringes with unified lattice directions (highlight with different color) along the array structure. In addition, defined atomic arrangements and lattice intersections with selective defective characteristics can be detected in the high-resolution TEM micrograph (Fig. 4h). Fig. 4i presents the FFT pattern, which contains a well-organized pattern of Moire fringes that represent the high-quality crystalline behavior of the prepared MXene/Fe3O4 nanocomposites.
To prepare the device prototypes, the current-density voltage (J–V) characteristics were detected at 100 mW cm−2 under AM 1.5G solar radiance for the pure PCBM ETL and different nanostructures (MXene, ZnO, Fe3O4, MXene/ZnO, and MXene/Fe3O4) using modulated PCBM ETL–encompassed solar cells. Different weight percentages of the nanostructures (1, 1.5, 2, and 2.5 wt%) were doped with PCBM to form effective ETLs and their properties were assessed. Fig. 6a displays the J–V curves of constructed devices with pure PCBM and 2 wt% MXene, ZnO, Fe3O4, MXene/ZnO, and MXene/Fe3O4 using modulated PCBM ETL-encompassed perovskite solar cells. A prepared device using a Cs0.1MA0.9PbI3 active layer with a pure PCBM ETL produced an excellent open circuit voltage (VOC) and short-circuit current density (JSC) of 0.895 V and 20.5 mA cm−2, respectively. Moreover, the prepared device explores 10.58% of PCE along with 57.6% of fill factor (FF), which were higher than those of the device composed of a pure MAPbI3 active layer (8.92%), as reported previously.4 When devices were prepared with different amounts of ZnO (1–2.5 wt%) using the modulated PCBM ETL, the J–V characteristics fluctuated surprisingly based on the amount of doping ZnO nanostructures. Fig. S11† displays the J–V characteristics of perovskite solar cells with 1, 1.5, 2, and 2.5 wt% of ZnO-doped PCBM ETL. Here, including ZnO with PCBM ETL produced significant improvements in the device performance, as demonstrated in Table S1.† The PCE of the constructed devices significantly improved to 10.31%, 11.23%, and 11.67% for 1, 1.5, and 2 wt% of ZnO-doped PCBM ETL devices, respectively. However, a device realizes the decrement of PCE beyond 2 wt% of ZnO doping with the PCBM ETL, whereas the PCE reduced to 10.88% for the prepared device with 2.5 wt% of ZnO-doped PCBM ETL.
The J–V characteristics were modulated based on the amount of MXenes doped with the PCBM ETL, and the results are provided in Fig. S12.† As expected, including MXenes with the PCBM ETL enriched device performances significantly, as demonstrated in Table S2.† When the PCBM was doped with 1 wt% of MXenes to make the ETL, the resulting device achieved a PCE of 11.21%. Moreover, devices incorporating 1.5 and 2 wt% of MXene-modulated PCBM ETL realized PCEs of 12.12% and 12.84%, respectively, whereas the device with 2.5 wt% of MXene-doped PCBM ETL achieved a low PCE of 11.73%. This could be due to the high amount of doping altering the core of the PCBM matrix. Fig. S13† displays the J–V profiles of modulated PCBM ETL devices composed of different amounts of Fe3O4. The prepared devices exhibit PCEs of 10.81%, 11.78%, 12.23%, and 11.26% for devices constructed with 1, 1.5, 2 and 2.5 wt% of Fe3O4-doped PCBM ETL (Table S3†). The observed results with Fe3O4-modulated ETL give a similar trend of device performance, as discussed previously.
To reveal the effect of the amalgamated matrix on ETL fabrication, MXene/Fe3O4 and MXene/ZnO nanocomposites were introduced with different doping percentages, and the results are provided in Fig. 6b and c, respectively. Table S4† elaborates on the perovskite solar cell parameters with different amounts of MXene/Fe3O4-modulated ETLs. A device composed of 1 wt% of MXene/Fe3O4 using modulated ETL realized improved J–V characteristics. The estimated parameters were VOC = 0.901 V, JSC = 22.2 mA cm−2, PCE = 12.24%, and FF = 61.2%. When the doping content of MXene/Fe3O4 was increased to 1.5 wt% in the ETL, the following were observed for the prepared device: VOC = 0.906 V, JSC = 22.9 mA cm−2, PCE = 13.25%, and FF = 63.7%. Superior device performance was achieved for 2 wt% of MXene/Fe3O4 using the modulated ETL-incorporated perovskite solar cell device with a maximum PCE of 13.79% and VOC = 0.902 V, JSC = 23.4 mA cm−2, and FF = 65.2% of. Further, 2.5 wt% of MXene/Fe3O4-modified ETL achieved a PCE of 12.76%. Table S5† elaborates on the perovskite solar cell parameters with different amounts of MXene/ZnO-modulated ETLs. When 1 wt% of MXene/ZnO was used to modulate the ETL, the prepared device achieved a VOC of 0.884 V, a JSC of 21.4 mA cm−2, a PCE of 11.86%, and an FF of 62.7%. Further, 1.5 wt% MXene/ZnO in the ETL created a PCE of 12.82% with a VOC of 0.908 V, a JSC of 22.4 mA cm−2, and an FF of 62.9%. A maximum PCE of 13.31% was realized for 2 wt% of MXene/ZnO using the modulated ETL-incorporated perovskite solar cell device in addition to a VOC of 0.904 V, a JSC of 22.9 mA cm−2, and an FF of 64.1%. Further, 2.5 wt% of MXene/ZnO-modified ETL achieved a PCE of 12.34%. These J–V characteristics clearly proved that 2 wt% doping of nanostructures produced efficient variations in the device performance. The observed device characteristics for pure PCBM and 2 wt% MXene, ZnO, Fe3O4, MXene/ZnO, and MXene/Fe3O4 using modulated PCBM ETL are provided in Table 1.
Device | V OC [V] | J SC [mA cm−2] | FF [%] | PCE [%] | R S [Ω cm2] |
---|---|---|---|---|---|
PCBM (ETL) | 0.895 | 20.512 | 57.63 | 10.58 | 169.31 |
ETL with ZnO | 0.897 | 21.623 | 60.16 | 11.67 | 158.42 |
ETL with Fe3O4 | 0.907 | 22.037 | 61.18 | 12.23 | 150.17 |
ETL with MXene | 0.905 | 22.598 | 62.78 | 12.84 | 143.18 |
ETL with Mxene@ZnO | 0.904 | 22.987 | 64.05 | 13.31 | 138.76 |
ETL with Mxene@Fe3O4 | 0.902 | 23.421 | 65.27 | 13.79 | 132.65 |
The perceived outcomes determined the maximum responsive characteristics of prepared devices with the 2 wt% of nanostructure-doped ETL. Hence, external quantum efficiency (EQE) measurements were conducted for pure and optimum MXene, ZnO, Fe3O4, MXene/ZnO, and MXene/Fe3O4 nanostructures using modulated PCBM ETL-composed solar cells, as displayed in Fig. 7a. The EQE measurements were conducted between wavelengths of 300 and 800 nm. A device composed of pure PCBM ETLs produces approximately 60% of the EQE curve in the visible region of wavelengths owing to their intrinsic characteristics.64 Further, the EQE profile evidently increased for the 2 wt% of nanostructure-doped ETL-composed devices. A trend of EQE profile suddenly increasing was observed (from a null to 88%) between the 300 and 600 nm wavelengths for the 2 wt% MXene/Fe3O4-doped PCBM ETL-incorporated device. In addition, the EQE declined slightly at the end of the visible region and increased significantly again at the near-IR region. A similar trend was observed for different ETL-composed devices, which could be caused by the interaction barrier between the active and transport layers during the charge carrier transport. The visible region of the EQE spectra enhancement could also be attributed to the enhanced JSC of the resulting devices.65 The establishment of an enriched photocurrent was primarily attributed to the enhanced charge carriers’ mobility (to some degree), rather than the altered light collecting properties of the devices.66Fig. 7b presents the UV-Vis-NIR absorption outlines of pure and 2 wt% MXene, ZnO, Fe3O4, MXene/ZnO, and MXene/Fe3O4 using modulated PCBM ETLs. The observations realized the considerable improvement of absorption characteristics due to the 2 wt% of nanostructures doping with PCBM ETL which authorized the enhanced light reaping characteristics of doped ETLs. These characteristics emanate from the improved surface interactions between the active layer and the ETL.
To reveal the origin of device performance, we investigated the charge transportation characteristics using PL studies for PCBM (ETL) and their hybridization with ZnO, Fe3O4, MXene, MXene/ZnO, and MXene/Fe3O4 onto ITO (Fig. 8a). All these layers exhibited a clear PL peak at 760 nm, which resulted from MAPbI3.67 The results indicated that the quantum yield of perovskite PL was significantly reduced for hybrid composites that included the PCBM ETL. This could be due to the inhibition of electron–hole pair recombination processes caused by PL quenching related to the increased performance of photoconversion. It was revealed that PL quenching efficiency was in the following order: PCBM (ETL) < ETL with ZnO < ETL with Fe3O4 < ETL with MXene < ETL with MXene/ZnO < ETL with MXene/Fe3O4. Atomic force microscopic (AFM) measurements were conducted to study the topographical properties of nanostructure-doped ETLs (Fig. 8b–g). The topologies of the prepared PCBM layers clearly exhibit peculiar alterations due to the doping of different nanostructures. The observed surface roughness was approximately 10.6, 10.1, 4.95, 3.34, 2.71, and 2.28 nm for the pure and MXene, ZnO, Fe3O4, MXene/ZnO, and MXene/Fe3O4-doped ETLs, respectively. The diminished surface roughness for the nanostructure-blended ETLs strongly suggests strong interfacial characteristics with the perovskite active layer and electrode, thereby achieving high device performances. Furthermore, the incorporated nanostructures could fill the voids and defective areas of the PCBM matrix, thereby offering compact surface characteristics for ETL formation and allowing many photo-generated carriers through the ETL for enhanced recombination properties.68 The comparable PCE improvements as elaborated in Table S6† with various literature studies strongly ascertained the improved device characteristics due to the inclusion of MXene/Fe3O4 and MXene/ZnO-modified ETLs.
(1) |
(2) |
The photodetection parameters of the CCD–DCD and the detection sensitivities were measured for different ETL-composed devices, as displayed in Table 2. The estimated results explored that the MXene/ZnO and MXene/Fe3O4 nanocomposite-blended PCBM ETL-integrated devices achieved high sensitivities of 4.41 and 4.63 mA per Gy per cm2, respectively. These results are superior to the other ETL-composed devices such as pure PCBM (3.12 mA per Gy per cm2), MXene@PCBM (4.16 mA per Gy per cm2), ZnO@PCBM (3.64 mA per Gy per cm2), and Fe3O4@PCBM (3.87 mA per Gy per cm2). The collected CCD-DCD were at 10.42, 13.89, 12.16, 12.93, 14.73, and 15.46 μA cm−2 for the pure and the 2% of MXene, ZnO, Fe3O4, MXene/ZnO, and MXene/Fe3O4 nanostructure-doped PCBM ETLs, respectively. Moreover, the measured JSC values were 20.5, 22.6, 21.6, 22.0, 22.9, and 23.4 mA cm−2, respectively, for the pure and optimum MXene, ZnO, Fe3O4, MXene/ZnO, and MXene/Fe3O4-doped PCBM hybrid ETLs, respectively, as illustrated in Table 2. Different concentrations (1, 1.5, 2, and 2.5 wt%) of MXene, ZnO, Fe3O4, MXene/ZnO, and MXene/Fe3O4 blended with the PCBM ETL comprising the X-ray detector device characteristics are specified in the Tables S7–S11,† respectively. The improvement in device performance was credited to the increased energy level synchronization between PCBM and the nanostructures, which could effectively reorganize the surface regulation, thereby easing swift carrier transport and boosting the charge collection efficiency at the interface.
Device | CCD–DDC [μA cm−2] | Sensitivity [mA per Gy per cm2] | Conductivity [S cm−1] |
---|---|---|---|
PCBM (ETL) | 10.42 | 3.12 | 412.23 |
ETL with ZnO | 12.16 | 3.64 | 481.78 |
ETL with Fe3O4 | 12.93 | 3.87 | 533.14 |
ETL with MXene | 13.89 | 4.16 | 591.57 |
ETL with Mxene@ZnO | 14.73 | 4.41 | 612.11 |
ETL with Mxene@Fe3O4 | 15.46 | 4.63 | 632.23 |
The capability of the prepared highly efficient X-ray detector using the MXene/Fe3O4-doped PCBM ETL was analyzed using different operation conditions. To determine the role of the applied X-ray source on device behavior, different applied voltages of −0.2 to −1.0 V were used to analyze device sensitivity and CCD–DCD. Fig. 10a displays the CCD–DCD and detection sensitivity of the MXene/Fe3O4-doped PCBM hybrid ETL-composed detector. The linear enhancement observes with the amount of applied voltage for the constructed X-ray detector. A maximum sensitivity of 4.92 mA per Gy per cm2 was observed with an applied voltage of −1.0 V for the prepared X-ray detector using the MXene/Fe3O4-doped PCBM ETL. Moreover, the observed CCD–DCD was between 14.4 and 16.43 μA cm−2 at the various applied voltages of the prepared X-ray detector (Fig. 10a, right panel).
Fig. 10 (a) CCD–DCD and sensitivity at different applied bias voltages. (b) Different dose rate performance of MXene/Fe3O4-doped PCBM ETL using the fabricated X-ray detector. |
In addition, to define the prepared X-ray detector responsivity, different absorbance doses (1.19, 2.28, 3.34, 4.47, and 5.56 m Gy) were incident on the detector to evaluate their capacity. Fig. 10b portrays the CCD–DCD variations in terms of different absorbed X-ray dosages on the MXene/Fe3O4-doped PCBM hybrid ETL-composed detector. The results strongly confirmed the enhancement at the rate of absorbance dose for the prepared X-ray detectors. Hence, the nanocomposite-incorporated ETL devices achieved enhanced detection properties, including a superior hybrid interfacial structure, smooth morphology, good energy level alignment with the active layer, and suppressed rate of carrier recombination, which allow for easy electron transportation/extraction and rapid exciton charge dissociation.
Footnotes |
† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d3nr01196h |
‡ These authors contributed equally. |
This journal is © The Royal Society of Chemistry 2023 |