The development of energy-efficient, bright, and flexible light-emitting devices has been a driving force in creating new flexible displays[
Journal of Semiconductors, Volume. 46, Issue 7, 072801(2025)
Green perovskite CsPbBr3 light-emitting electrochemical cells with distributed Si nanowires-based electrodes for flexible applications
The emergence of cesium lead halide perovskite materials stable at air opened new prospects for the optoelectronic industry. In this work we present an approach to fabricating a flexible green perovskite light-emitting electrochemical cell (PeLEC) with a CsPbBr3 perovskite active layer using a highly-ordered silicon nanowire (Si NW) array as a distributed electrode integrated within a thin polydimethylsiloxane film (PDMS). Numerical simulations reveal that Si NWs-based distributed electrode aids the improvement of carrier injection into the perovskite layer with an increased thickness and, therefore, the enhancement of light-emitting performance. The X-ray diffraction study shows that the perovskite layer synthesized on the PDMS membrane with Si NWs has a similar crystal structure to the ones synthesized on planar Si wafers. We perform a comparative analysis of the light-emitting devices’ properties fabricated on rigid silicon substrates and flexible Si NW-based membranes released from substrates. Due to possible potential barriers in a flexible PeLEC between the bottom electrode (made of a network of single-walled carbon nanotube film) and Si NWs, the electroluminescence performance and I ? V properties of flexible devices deteriorated compared to rigid devices. The developed PeLECs pave the way for further development of inorganic flexible uniformly light-emitting devices with improved properties.
Introduction
The development of energy-efficient, bright, and flexible light-emitting devices has been a driving force in creating new flexible displays[
Cesium lead halide perovskite CsPbX3 (X = Cl, Br, I) materials opened new prospects for the optoelectronic industry[
However, mechanical and electrical stability is crucial for developing flexible devices both on organic and perovskite material[
In this work, we propose the integration of distributed electrodes based on highly doped and ordered Si NWs to the flexible PeLEC light emitting layer. The considered Si NW arrays have great uniformity thanks to the processing approach based on microsphere lithography combined with dry plasma etching. The integration of lead halide perovskites with Si NWs into flexible structure enables the development of more efficient, cost-effective, and versatile optoelectronic devices, such as solar cells[
Figure 1.(Color online) (a) Schematic presentation of the conventional design of a flexible planar perovskite light-emitting device (on the left) and flexible perovskite device with a distributed Si NWs electrode (on the right). (b) Fabrication workflow of a flexible PeLEC with a distributed Si NW-based electrode. (c) Photo of the bent PeLEC membrane with a distributed Si NW-based electrode; scale bar is 1 cm.
Materials and methods
Numerical simulation
To evaluate the efficiency of the light-emitting devices based on the hybrid n-Si NWs/CsPbBr3 structures, numerical simulation was conducted. We employed the drift-diffusion model in axial-symmetrical 2D geometry for Si/perovskite/SWCNT structure (electron-emitter/active material/hole-emitter). Non-ideality of electrical contacts was not taken into consideration. CsPbBr3 material properties were adopted from Refs. [
Silicon NW array fabrication
The Si NW arrays were fabricated using microsphere lithography and dry plasma etching in an SF6/O2 gas mixture at cryogenic temperature[
In this work, we used the n-type antimony doped silicon (100) wafers (the resistivity of 0.013−0.015 Ω·cm). The process began with plasma-chemical deposition (CVD) of a 500 nm thick SiO2 layer on a Si substrate using Oxford Instruments PlasmaLab 100 PECVD equipment (United Kingdom). Then, by the means of microsphere mask lithography, a template on the SiO2/Si surface was formed. For this purpose, a monolayer of 2 μm in diameter polystyrene spheres was deposited from a colloidal solution by spin-coating at 700 r/mim for 1 min.
The fabrication of Si NWs through the microsphere mask included three dry etching steps. First, the diameter of polystyrene spheres was reduced by O2 plasma etching; second, the SiO2 layer was etched in CHF3 plasma through the mask of polystyrene spheres; finally, inductive-coupled plasma (ICP) cryogenic etching of Si through the formed hard SiO2 mask was performed. The following parameters providing a vertical etching profile were employed: SF6 flow of 50 sccm, O2 flow of 9 sccm, RF power of 30 W, ICP power of 1000 W, and temperature of −120 °C. The plasma etching process was carried out using the Oxford Plasmalab System 100 ICP380 (United Kingdom) setup.
Figure 2.Isometric SEM images of (a) an etched Si NW array; (b) a Si NWs array after PDMS coating; (c) the revealed top parts of Si NWs in the partially etched PDMS membrane. Inset in (a) shows a cross-section view SEM image of an as-fabricated Si NW array. The scale bars for all images are 2 µm.
Fabrication of Si NW-based distributed electrode
The fabrication of the Si NW-based distributed electrodes involves several steps. First, a 5 nm thick layer of Yb was deposited on Si NW top parts by e-gun evaporation using Boc Edwards (UK) Auto 500 setup (vacuum of 3 × 10−5 mbar) to protect Si NWs during further O2/CF4 etching of polymer. For the Si NWs/polymer membrane fabrication, a commercial polydimethylsiloxane (PDMS) (Dow Corning Sylgard 184) was mixed in a standard base-to-curing agent ratio of 10 : 1. The mixture was dropped onto a Si NW array and distributed via the G-coating method (5000 r/mim for 60 min)[
An O2/CF4 plasma etching was used to partially reveal the Si NW top parts above the PDMS surface (for further electrical contact) and maintain a uniform PDMS membrane thickness of approximately 3−4 μm. Finally, the protective Yb layer was removed selectively from NWs in hydrochloric acid (HCl) at a concentration of 1 : 10 for 2 min. The sample surface and thickness of the polymer layer were analyzed by SEM.
For on-silicon rigid devices (not released from rigid Si substrates), the bottom electrode consisting of a 100 nm thick Al layer was deposited on the Si substrate backside by e-gun evaporation using a Boc Edwards (UK) Auto 500 setup at 3 × 10−5 mbar.
Fabrication of CsPbBr3 emission layer
A CsPbBr3 solution (molar concentration of 0.2 mmol/mL) was prepared in a dry nitrogen atmosphere by dissolving lead (II) bromide salt (PbBr2) (99.9% purity, Lankhit) and cesium bromide salt (CsBr) (99.9% purity, Lankhit) in anhydrous dimethylsulfoxide (DMSO) (99.8% purity, Sigma Aldrich) solvent and stirred overnight at 60 °C and 300 r/mim. The polyethylene oxide (PEO) (Sigma-Aldrich) solution (concentration 10 mg/mL) was prepared in an inert atmosphere of nitrogen by adding PEO powder (Mw = 1 000 000) in DMSO; to dissolve the polymer, the mixture was stirred overnight at 60 °C and 300 r/mim. The perovskite-polymer composite solution (CsPbBr3 : PEO/DMSO) was prepared in the ambient condition by mixing PEO and CsPbBr3 solutions in a 1 : 0.13 weight ratio of dry components. Then, the perovskite-polymer solution was mixed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) (anhydrous, 99.99% trace metals basis, Sigma-Aldrich)/DMSO solution (concentration of 10 mg/mL) with a ratio of 1 : 0.01 by weight. This final solution was stirred for 1 h at 60 оC and 300 r/mim.
Prior to perovskite-polymer composite spin-coating, the sample surface was treated in RF oxygen plasma (power of 400 W) for 1 min. To obtain a light-emitting layer, the composite perovskite thin film was spin-coated on the top of the revealed Si NWs and annealed at 60 or 200 °C on a hot plate (see the fabrication workflow in
Fabrication of SWCNT transparent flexible electrodes for PeLEC device
SWCNTs were synthesized by an aerosol (floating catalyst) chemical vapor deposition method using CO as a carbon source and ferrocene as a catalyst precursor[
After CsPbBr3 : PEO layer formation, a flexible top electrode, made of 90% transparent SWCNT film with 84 Ω/square sheet resistance[
Processing of flexible membrane-based PeLEC
For flexible membrane-based PeLEC processing, the PDMS-encapsulated Si NW array with the already formed perovskite film and SWCNT-based top electrical contact were released from the rigid silicon substrate. Before delamination, to protect the perovskite layer from mechanical and environmental impact, the sample was coated with a supporting layer of PDMS (average thickness of 500 μm) and annealed on the hot plate at 60 °C for 5 h. Additionally, this PDMS layer provides mechanical support to the membrane, enabling easier membrane release. The protected membrane with PeLED was mechanically removed from the Si substrate using a microtome blade. Bottom electrical contact to the Si NWs array was formed at the cut interface from SWCNTs pads via the previously described approach (see
Structural and optoelectronic characterization
The perovskite films structural characterization was performed using a Bruker Kappa Apex II diffractometer (Germany) equipped with a microfocus Incoatec ImS 1.0 Cu−Ka X-ray source (1.5418 Å) and 2D charge-coupled detector (Apex CCD). Perovskite film samples were mounted with the surface normal to the phi axis of rotation. X-ray diffraction (XRD) patterns were collected at a grazing incidence angle of 10° with an exposure time of 10 min. Samples were rotated a full 360° around the phi-axis to obtain uniform diffraction rings. The acquired 2D diffraction patterns were integrated into 2θ-intensity profiles using DIOPTAS software[
To analyze film texturing, three-dimensional (3D) reciprocal space maps (RSMs) were acquired by performing a full 360° phi-scan with an angular step of 0.5°. The reciprocal space intensity distribution was reconstructed using RecSpaceQt software[
Photoluminescence (PL) spectra were acquired using a mercury lamp (i-line with a wavelength of 365 nm) and recorded using the Ocean Optics QE Pro optical fiber spectrometer (USA) coupled with a Carl Zeiss Axio Imager A2m (Germany) microscope operating in a fluorescent regime. The detection area was a spot of 2 μm in diameter. The fluorescent images of the samples were obtained using the previously mentioned microscope with a 100× objective EC Epiplan-NEOFLUAR (Carl Zeiss).
The current−voltage characteristics (I−V curves) of the fabricated device were acquired using a Keithley 2401 source meter. Data on device EL was collected with a Telescopic Optical Probe 150 of CAS 120 Instrument Systems spectroradiometer.
Results and discussion
Numerical simulation of n-Si NWs/CsPbBr3 PeLEC system
We performed numerical simulation of the band structure and optoelectronic properties of the considered hybrid perovskite/Si NWs system. The model consisted of n-doped Si NW, partially embedded into a perovskite layer (
Figure 3.(Color online) (a) Schematic view of the considered semiconductor system. (b) The calculated system band diagram at the Si NWs/CsPbBr3 interface (transverse coordinate). (c) The system’s calculated current density and radiative recombination quantum efficiency dependencies over the applied voltage (for the fixed Hemb = 500 nm, DNW = 100 nm, L = 1000 nm, P = 0.2 μm−2). Insert shows the distribution of radiative recombination rate in the cross-section of the PeLEC structure. The calculated maps of quantum efficiency on (d) NW surface density and NW diameter (for the fixed Hemb = 500 nm and L = 1000 nm) and (e) perovskite thickness and NW height embedded into the active perovskite layer (for the fixed DNW = 75 nm and P = 0.2 μm−2).
The insert in
To achieve a balance between mechanical and electrical properties, the NW morphology parameters, such as diameter and height, should be in the certain range. We also calculated dependencies of current density, passing through the entire PeLEC structure, on the NW parameters (Fig. S2(a) in the Supplementary materials). For the chosen NW array density (defined by the diameter of microspheres employed for Si etching), the optimal NW diameter corresponds to the range of (300−800 nm). Although, according to
Moreover, NWs with diameter lower than critical one drastically lose their conductivity due to significant influence of surface defects (since the part of the conductive NW channel is depleted[
At the same time, increasing both the height of Si NW embedded into the perovskite (Hemb) and the perovskite thickness (L) boosts device performance (see
At the same time, according to our experimental results, the minimal height of Si NWs array allowing the encapsulation into the PDMS layer and its further release from the substrate is above 4 μm (due to viscosity of the polymer and its mechanical strength, also see Ref. [
Hence, the Si NWs-based distributed electrode (compared to the planar one) provides not only the structure's mechanical flexibility but also helps to improve the carrier injection into the perovskite layer with an increased thickness, which, in turn, enhances the light-emitting performance.
According to the results of numerical calculations, the NW height and diameter were chosen as 4.2 and 0.8 μm, respectively, while the period of the array was 2 µm (defined by the diameter of the employed polystyrene spheres)—see SEM images in
Impact of CsPbBr3:PEO processing parameters on film crystallization
To investigate the influence of the spin-coating parameters on the resulting perovskite layer thickness, perovskite films were spin-coated on Si NW arrays at 600, 800, 1000, and 1200 r/mim. Due to the non-planar Si NWs array surface and composite perovskite-polymer solution's relatively high viscosity, the rotation speed (600−1200 r/mim) during spin-coating does not significantly affect the thickness of the acquired layer, which is approximately 2 µm.
Figure 4.(Color online) (a) Cross-sectional SEM images of perovskite layers, spin-coated at 600 and 1200 r/mim on Si NWs membranes (presented in artificial colors for clarity); the insets show the corresponding top-view PL images. (b) PL spectra of CsPbBr3 layers obtained with different coating speeds. (c) Isometric SEM images of CsPbBr3 layers spin-coated on Si NWs membranes at 600 r/mim and annealed at 60 and 200 °C; the insets show the corresponding top-view PL images. (d) PL spectra of CsPbBr3 layers obtained with different temperatures of annealing. (e) XRD patterns for a series of CsPbBr3 perovskite films spin-coated on Si NW membranes and planar Si substrate. The calculated positions of the Bragg reflections related to the CsPbBr3 (COD CIF file ID: 4510745)[47] and Cs4PbBr6 (COD CIF file ID: 4002857)[48] phases are shown by black and green vertical marks, correspondingly.
Additionally, perovskite solution was spin coated on Si substrate using a wide speed range up to 5000 r/mim (keeping other parameters the same) and 60 oC annealing temperature. The thickness of the spin-coated layers was estimated using cross-section SEM imaging. As shown in Fig. S4 in the Supplementary materials, higher spin-coating speed results in the decrease of CsPbBr3 film and, therefore, the drop of photoluminescence (Fig. S5 in the Supplementary materials). We suggest to use Si NWs as distributed electrodes, embedded into luminescence perovskite layer, to achieve better conductivity for thick films. According to our calculations, increasing the perovskite layer thickness allows to achieve higher device performance. Thus, we suggest that the chosen spin-coating speed from 600 to 1200 r/mim corresponds to the optimal processing window for achieving the desired balance between film thickness, luminescence performance, and charge transport efficiency in our devices.
Then, we investigated the influence of annealing temperature (Tann) on the quality of perovskite layer spin-coated at 600 r/mim on Si NW arrays. Annealing at Tann = 60 °C, corresponding to typical annealing temperatures for PeLECs[
CsPbBr3 perovskites crystals have two main symmetries: low-temperature (orthorhombic) and high-temperature (cubic). Cubic symmetry occurs above 130 °C, however it is unstable and changes to orthorhombic symmetry at lower temperatures (<88 °C)[
Despite the similar XRD patterns, a significant difference was observed in the intensity distribution of the diffraction rings among the studied samples. The 2D-RSMs obtained from the CsPbBr3 layer deposited on the Si wafer show solid diffraction rings with almost uniform intensity, indicating the isotropically oriented crystalline grains. In contrast, the perovskite film deposited on the Si NWs exhibited spotty diffraction rings, suggesting possible grain coarsening and formation of larger crystallites. Moreover, grain coarsening was more pronounced in the layer annealed at 60 °C compared to the structure annealed at 200 °C. These observations lead to the conclusion that the formation of CsPbBr3 layers on the Si NWs results in different grain sizes (compared to planar substrate) but does not lead to the appearance of preferential orientation or stabilization of unwanted metal bromide salts or Pb- or Cs-rich perovskite phases.
Thus, to avoid the double emission peak, and achieve lower FWHM and more uniform perovskite coverage, going forward, for flexible PeLEC fabrication we employed composite perovskite-polymer layers, spin-coated on Si NW membranes at 600 r/mim and annealed at 60 °C.
PeLEC-on-Si and flexible PeLEC characteristics study
Figure 5.(Color online) (a) Сross-sectional SEM image of PeLEC-on-Si device (in artificial colors for clarity). Photo of (b) PeLEC-on-Si and (c) flexible PeLEC during EL measurements (acquired at 5 and 7.3 V applied voltage, respectively). (d) Luminance−voltage (red curve) and current density−voltage (black curve) dependencies for PeLEC-on-Si device, (e) EL spectra of PeLEC-on-Si and flexible PeLEC devices. (f) PeLEC-on-Si and flexible PeLEC I−V curves comparison.
Similarly, the flexible PeLEC device (obtained from the same PeLEC-on-Si device) was investigated functionally after releasing from the Si substrate and applying the bottom flexible SWCNT contact. The flexible PeLEC’s I−V curve is shown in
Conclusion
We have demonstrated perovskite PeLEC devices on Si substrates and flexible PDMS membranes with distributed electrodes based on the highly ordered uniform arrays of Si NWs. Numerical simulation has shown that a flexible Si NWs-based distributed electrode helps to improve the carrier injection to the perovskite layer with an increased thickness, which, in turn, enhances the light-emitting performance. It has been experimentally shown that spin-coating speed does not significantly influence the perovskite layer morphology for our device NWs-based geometry. At the same time, the annealing temperature modified the morphology from dendrites to uniaxial grains with size distribution while being increased from 60 to 200 oC. The performed XRD analysis has revealed that perovskite films crystallized at different temperatures, and substrate morphology had no significant difference in the crystal structure, while corresponding PL responses slightly differed. As a result of all optimization procedures, we have developed high-quality samples where the highly-ordered Si NW array, fabricated employing microsphere mask etching, provides uniform light emission over the PeLEC pixels both on rigid and flexible substrates. This paves the way for further developing bright and uniform flexible light-emitting devices.
Appendix A. Supplementary material
Supplementary materials to this article can be found online at
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Viktoriia Mastalieva, Anastasiya Yakubova, Maria Baeva, Vladimir Neplokh, Dmitry M. Mitin, Vladimir Fedorov, Alexander Goltaev, Alexey Mozharov, Fedor Kochetkov, Andrei S. Toikka, Ramazan Kenesbay, Ekaterina Vyacheslavova, Alexander Vorobyev, Kristina Novikova, Dmitry Krasnikov, Jianjun Tian, Albert G. Nasibulin, Alexander Gudovskikh, Sergey Makarov, Ivan Mukhin. Green perovskite CsPbBr3 light-emitting electrochemical cells with distributed Si nanowires-based electrodes for flexible applications[J]. Journal of Semiconductors, 2025, 46(7): 072801
Category: Research Articles
Received: Dec. 6, 2024
Accepted: --
Published Online: Aug. 27, 2025
The Author Email: Anastasiya Yakubova (AYakubova)