Research Article www.acsami.org
High-Performance Ultrathin Organic−Inorganic Hybrid Silicon Solar Cells via Solution-Processed Interface Modification Jie Zhang,†,‡ Yinan Zhang,‡,§ Tao Song,† Xinlei Shen,∥ Xuegong Yu,∥ Shuit-Tong Lee,† Baoquan Sun,*,† and Baohua Jia*,‡ †
Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Institute of Functional Nano and Soft Materials (FUNSOM) and Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou 215123, Jiangsu, China ‡ Centre for Micro-Photonics, Faculty of Science, Engineering, and Technology, Swinburne University of Technology, Hawthorn, Boroondara, Victoria 3122, Australia § Institute of Photonics Technology, Jinan University, Guangzhou 510632, Guangdong, China ∥ State Key Laboratory of Silicon Materials and Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, Zhejiang, China S Supporting Information *
ABSTRACT: Organic−inorganic hybrid solar cells based on n-type crystalline silicon and poly(3,4-ethylenedioxythiophene)−poly(styrenesulfonate) exhibited promising efficiency along with a low-cost fabrication process. In this work, ultrathin flexible silicon substrates, with a thickness as low as tens of micrometers, were employed to fabricate hybrid solar cells to reduce the use of silicon materials. To improve the light-trapping ability, nanostructures were built on the thin silicon substrates by a metal-assisted chemical etching method (MACE). However, nanostructured silicon resulted in a large amount of surface-defect states, causing detrimental charge recombination. Here, the surface was smoothed by solutionprocessed chemical treatment to reduce the surface/volume ratio of nanostructured silicon. Surface-charge recombination was dramatically suppressed after surface modification with a chemical, associated with improved minority chargecarrier lifetime. As a result, a power conversion efficiency of 9.1% was achieved in the flexible hybrid silicon solar cells, with a substrate thickness as low as ∼14 μm, indicating that interface engineering was essential to improve the hybrid junction quality and photovoltaic characteristics of the hybrid devices. KEYWORDS: flexible silicon, organic−inorganic hybrid, solar cells, chemical polishing, charge recombination
1. INTRODUCTION Tremendous efforts have been devoted over the last half a century to renewable energy technologies, especially silicon solar cells, to meet the ever-increasing energy consumption demand of human society. However, deployment of large-scale photovoltaic (PV) energy is still limited by the high fabrication cost of the market-dominant silicon solar cells.1−4 Because crystalline silicon is an indirect band gap semiconductor, silicon wafers, with a thickness of around 180−300 μm, are usually required to ensure sufficient light absorption,5−7 which make the solar cells rigid and bulky. Accordingly, light-weight flexible solar cells based on thin silicon wafers, below 100 μm in thickness, have attracted substantial attention for their potential applications, such as portable rechargers, building integrated PVs, etc.8,9 In the fabrication processes of conventional silicon solar cells, high-temperature processes, over 800 °C, such as dopant diffusion and electrode firing, are usually employed to form p− n junctions and Ohmic contacts.4,10−12 Meanwhile, the surface © 2017 American Chemical Society
passivation and antireflective layers of SiNx are typically fabricated by the plasma-enhanced chemical vapor deposition method. The thermal budget and equipment maintenance of these processes stand for a major part of the fabrication cost of silicon solar cells, in addition to the expensive silicon wafers. It is highly desirable to substitute these costly and energyconsuming processes with economical low-temperature fabrication technologies to realize the cost-effectiveness of silicon solar cells. As a result, research attention has been paid to organic−inorganic hybrid silicon solar cells fabricated with simple low-temperature solution processes.13−15 The organic layers could be easily deposited onto silicon substrates at room temperature to form organic−inorganic heterojunctions by various solution-casting methods, such as spin coating,16 inkjet printing,17 and dip coating.18 The conductive polymer poly(3,4Received: February 14, 2017 Accepted: June 12, 2017 Published: June 12, 2017 21723
DOI: 10.1021/acsami.7b02140 ACS Appl. Mater. Interfaces 2017, 9, 21723−21729
Research Article
ACS Applied Materials & Interfaces
2. EXPERIMENTAL SECTION
ethylenedioxythiophene)−poly(styrenesulfonate) (PEDOT:PSS) has been widely used as hole-collecting layers in hybrid solar cells due to its high conductivity and stability.19 The PEDOT:PSS film exhibits metallic properties, with a deep work function of ∼5.0 eV, and could form a well-defined Schottky junction with silicon.20 Use of the organic−inorganic hybrid solar cell based on the PEDOT:PSS/n-Si heterojunction has been extensively investigated as one of the potential techniques to realize low-cost PV application.21 Especially, these light-weight flexible hybrid solar cells based on ultrathin silicon layers have achieved impressive PV performances, with a significantly reduced amount of silicon material consumption,13,22 even under curve surface applications, and almost stable performance, benefited from the unique fabrication technique and reduced individual device area, thereby giving a robust device reliability and reduced light absorption nonuniformity. However, further improvement in the conversion efficiency sees a major challenge due to the significantly reduced light absorption when the silicon layer is ultrathin. Silicon nanostructures, such as silicon nanowires (SiNWs),23 silicon nanoholes (SiNHs),24 silicon nanocones,25 nanopores,26 and other nanostructures,5,27 provide a low reflectivity over a broad wavelength range in the solar spectrum, making them promising light-weight flexible substrates for solar cells due to their light-harvesting capability compared with planar silicon wafers with an equivalent volume. However, the light-trapping nanostructures significantly enlarge the surface area of the silicon substrates and induce additional surface trap states, leading to a high surface recombination velocity and reduced PV performance. Therefore, an effective surface passivation layer is necessary to ensure minimal surface recombination and long minority charge-carrier lifetime in a high-performance PV device. Several surface passivation strategies have been demonstrated to improve the power conversion efficiency (PCE) of nanostructured silicon solar cells, such as SiOx,20,28 allyl monolayers,16 and organic thin films.21,29 Recently, an Al2O3 nanoparticle solution was deposited onto silicon substrates of only ∼8.9 μm to increase the light absorption of thin silicon PV devices, and a PCE as high as 7.7% was obtained.4 Also, an ultrathin atomic layer of Al2O3 was introduced as an interface passivation layer between the silicon nanochannel arrays and the PEDOT:PSS layer, leading to enhanced electrical performance.30,31 On the other hand, to avoid the light shadow effect from metal grid, the all-backcontact design was applied on silicon solar cells with a thermally diffused p−n junction.4 The all-back-contact design prevented the Auger recombination loss near the front surface. Nevertheless, the involved high-temperature thermal diffusion process and complicated back-contact formation techniques were not cost-effective compared to those of the lowtemperature solution fabrication method. In this study, convenient and economical low-temperature solution processes were employed to fabricate high-performance solar cells based on nanostructured flexible silicon, which was prepared by a facile solution etching method. Subsequent solution treatments were carried out to suppress the surface recombination. PEDOT:PSS was spin-coated onto the asprepared flexible substrate to form a conformal organic− inorganic hybrid heterojunction. By controlling the surface morphology, a PCE of up to 9.1% was achieved, which was one of the best performances for flexible ultrathin organic-silicon hybrid solar cells fabricated by a low-temperature process.
Thin silicon was etched from bulk n-type (100) silicon wafers (0.05− 0.1 Ω cm, 290 ± 20 μm thickness). The substrate was immerged in a potassium hydroxide solution with a concentration of ∼50 wt % at ∼90 °C for different time durations to acquire thin silicon substrates with various thicknesses. Nanostructured silicon was prepared by dipping the ultrathin flexible substrate into an aqueous solution of AgNO3 (0.02 M) and HF (4.8 M) at room temperature. After the substrate was rinsed with deionized water, it was immersed into HNO3 and HF solutions sequentially. The ultrathin nanostructured silicon substrate was then dipped into 1 vol % tetramethylammonium hydroxide (TMAH) solution for 25 s at room temperature to reduce the surface area of nanostructured silicon. Absorption and reflection spectra were recorded with a LAMBDA 750 spectrophotometer. PEDOT:PSS (CLEVIOS PH 1000, with 5 wt % dimethyl sulfoxide (DMSO) and 1 wt % Triton) solution was spin-casted onto the ultrathin nanostructured silicon substrate at 9000 rpm for 1 min. Then, the substrate was annealed at 125 °C in an inert atmosphere. Finally, a 200 nm thick Ag top grid contact and a 200 nm thick Al back contact were deposited by a thermal evaporation process under 10−6 Torr (NANO 36, Kurt J. Lesker). Note that the coverage area of the Ag grid contacts (line width ∼100 μm) stands for approximately 10% of the whole device area (0.8 cm × 1 cm), which was defined by an opaque mask with a square hole. The current density−voltage (J−V) characteristics of ultrathin silicon solar cells were measured using a xenon lamp of 300 W and an air mass 1.5 filter equipped with a Newport 91160 solar simulator to generate simulated solar spectrum irradiation source. The irradiation intensity of the a simulated solar spectrum was 100 mW cm−2. External quantum efficiency (EQE) measurements were performed with a Newport 1918 power meter, which was equipped with a silicon detector, 918D, and a Newport monochromator, 74125. A Keithley 2612 source meter was used to record all of the electrical data. Scanning electron microscopy (SEM) images were obtained using an FEI Quanta 200 FEG. Transient photovoltage and photocurrent decay measurements were accomplished under steady white bias light. A 532 nm green laser pulse triggered by a signal generator was used to generate a small (∼10 mV) perturbation photovoltage. Transient decay of the perturbation photovoltage signals was recorded with a Tektronix oscilloscope, with an input impedance of 1 MΩ. The transient photocurrent decay was subsequently measured with an input impedance of 50 Ω. Minority carrier lifetime mapping measurements were carried out using the microwave photoconductivity decay mode of a Semilab WT2000 mPCD.
3. RESULTS AND DISCUSSION A thin silicon wafer on the order of a few micrometers is generally obtained by mechanically and chemically etching silicon on insulator wafers.7 Although a high uniformity can be achieved, it is rather costly due to the wastage of materials. There are alternative approaches to obtaining thin silicon, such as by induced cleavage1515 or a porous silicon-related method.32 Cleavage can be achieved by hydrogen implantation accompanied by stress induced by a thick metal layer. It is a low-cost method to obtain crystalline silicon with a thickness of 20−50 μm. The porous silicon-based method includes the generation of two layers with different porosities. The high porosity layer detaches away from the substrate. Both methods are economic methods, as the mother substrate can be reused. Herein, to simplify our fabrication process, planar silicon substrates with different thicknesses were obtained by potassium hydroxide solution etching of thick silicon wafers over various etching times.25 The cross-sectional view SEM images of silicon substrates with different thicknesses is shown in Figure S1, wherein a series of thicknesses of, that is, 225, 167, 74, 20, and 14 μm, have been considered, and the device performances are listed in 21724
DOI: 10.1021/acsami.7b02140 ACS Appl. Mater. Interfaces 2017, 9, 21723−21729
Research Article
ACS Applied Materials & Interfaces
Figure 1. (a) Optical image of an ultrathin flexible silicon wafer substrate. (b) White light penetrates through the ultrathin silicon (∼14 μm) substrate partially. (c) Top view SEM images of nanostructured silicon before TMAH treatment. High-resolution cross-sectional SEM image of the same sample is also shown in the inset. The scale bars in (c) and the inset were 3 and 1 μm, respectively. (d) Top view SEM images of nanostructured silicon treated with TMAH. High-resolution cross-sectional SEM image of the same sample is also shown in the inset. The scale bars in (d) and the inset are 3 and 2 μm, respectively.
Figure 2. Energy band alignment diagrams of flexible silicon substrates with (a) a planer surface, (b) an as-prepared SiNWs surface, and (c) a TMAH-treated SiNW surface. The lightning symbols stand for the charge recombination processes. CB: conducting band energy; VB: valence band energy.
ogy due to the random redox etching process catalyzed by silver clusters, which leads to a high density of surface traps and an increase in undesirable surface-charge recombination. After the TMAH treatment, the long SiNWs (inset of Figure 1c) are dramatically shortened with only the bottom parts remaining, which results in a low surface/volume ratio. The remaining antireflective nanostructures are still distributed uniformly on the silicon surfaces after TMAH treatment, with an average height of a few hundred of nanometers Figure 1d. The surface morphology is dramatically changed with a reduction in surface area. The nanostructured silicon substrate is annealed after a layer of PEDOT:PSS film is spin-coated onto its surface, on which a thin SiOx layer is formed as the passivation layer. Thus, the surface recombination velocity is effectively suppressed because of the reduced surface area and effective passivation by the SiOx layer.33 The light-trapping property of the substrate is slightly reduced after the TMAH treatment because of the reduced density and aspect ratio of the antireflective
Table S1 of the Supporting Information. When the thickness is reduced to around 14 μm, the ultrathin silicon substrate becomes highly flexible, as shown in Figure 1a. Light absorption capability of silicon substrates decreased with a decrease in wafer thickness, as demonstrated by the light transmissivity spectra in Figure S2. Incident light in the near-infrared region penetrates the silicon substrate as the substrate becomes thinner. If the substrate is thinner than ∼14 μm, more than 10% of the visible light can travel through the ultrathin substrate, as shown in Figure 1b. To enhance light absorption, an antireflective nanostructure is fabricated onto the surface of the thin silicon substrates to minimize optical loss. Then, the nanostructured silicon surface is modified by anisotropic etching with TMAH5,16 to decrease the surface/volume ratio and suppress charge-carrier recombination. Figure 1c,d shows the SEM images of nanostructured silicon before and after TMAH treatment, respectively. The nanostructured silicon displays a very rough surface morphol21725
DOI: 10.1021/acsami.7b02140 ACS Appl. Mater. Interfaces 2017, 9, 21723−21729
Research Article
ACS Applied Materials & Interfaces
Figure 3. Minority carrier lifetime mapping images of the ∼14 μm thick silicon substrates with (a) a planar surface, (b) an as-prepared nanostructured silicon surface, and (c) a TMAH-treated nanostructured silicon surface.
nanostructures. When the wafer thickness is smaller than ∼20 μm, the entire solar cell becomes flexible. Detailed characterization of the solar cell performance versus different stress conditions, incident angles, areas, and solar cell thicknesses, which is outside the scope of the current work, would by interesting future work. Organic−inorganic hybrid solar cells based on the heterojunction between PEDOT:PSS and silicon substrates without the pinning effect exhibited promising PV performances. In this junction, the well-passivated surface of nanostructured silicon can reduce charge recombination in the presence of the PEDOT:PSS layer.34 The low-temperature solution-processed PEDOT:PSS layers acted as efficient transparent anodes due to their high transparency and excellent conductivity. The PCE of organic−inorganic hybrid solar cells is highly dependent on the interface condition on the silicon surfaces.35−38 Here, the energy band alignment diagrams of the organic−inorganic hybrid heterojunctions based on nanostructured silicon without or with TMAH treatments are shown in Figure 2. For planar flexible silicon solar cells, Auger recombination is normally the dominating losing mechanism of light-induced carriers in charge transportation, as shown in Figure 2a. After the MACE process, the surface area of the silicon substrate is dramatically increased, bringing in the severe surface recombination problem due to the high density of surface trap states in SiNWs, as shown in Figure 2b. So, both Auger recombination and surface recombination seriously limit the PCE of SiNWs devices. To suppress charge recombination processes in SiNWs, a subsequent TMAH solution treatment is introduced to modify the final surface morphology and control the surface area. Figure 2c demonstrates that the charge recombination processes at the organic−inorganic interface could be effectively suppressed by reducing the surface area and density of the surface trap states. Microwave photoconductance decay measurements were conducted to probe the minority carrier lifetimes of thin silicon substrates with different surface morphologies.21 By comparing the minority carrier lifetimes, the intensity of the charge recombination processes could be evaluated in quantity. The minority carrier lifetime of a silicon substrate is determined by both bulk recombination and surface recombination, which can be expressed by eq 111,21 1 τmeas
=
1 τbulk
+
2S W
measured minority carrier lifetimes of the silicon substrates reflected the intensity of surface recombination. Different samples with various surface morphologies, including (a) a planar substrate, (b) nanostructured silicon without TMAH treatment, and (c) nanostructured silicon treated with TMAH, were prepared as follows. All of the samples were coated with PEDOT:PSS to mimic the device condition. The minority carrier lifetime mapping images are illustrated in Figure 3. The planar ultrathin silicon substrate displays a relatively long minority carrier lifetime of 2.3 μs because the planar silicon substrate displays the minimum surface/volume ratio. The minority carrier lifetime of the nanostructured silicon samples prepared by the MACE method decreases to 0.7 μs owing to serious charge recombination on the surfaces. After the thin nanostructured silicon is treated with the TMAH etching process, the surface area and density of defect states are reduced substantially, resulting in a longer minority carrier lifetime of 1.3 μs. The minority carrier lifetime measurements reveal that the surface morphologies of nanostructured silicon can be rationally modified by TMAH treatments to obtain low surface recombination. PEDOT:PSS/Si hybrid solar cells based on ultrathin silicon substrates are fabricated to investigate the influence of different surface morphologies on the PV performance. Figure 4 illustrates the current density−voltage (J−V) curves of ultrathin silicon hybrid solar cells (∼14 μm) with planar silicon, nanostructured silicon with or without TMAH treatment, and the schematic device structure. Electric-output characteristics are summarized in Table 1. The device based on silicon with TMAH treatment displays an open circuit voltage (VOC) of 0.56 V, a short circuit current density (JSC) of 21.3 mA cm−2, and a fill factor (FF) of 0.76, yielding a PCE of 9.1%, whereas the device based on nanostructured silicon without TMAH exhibits a PCE of only 6.6%, with a VOC of 0.51 V, a JSC of 19.9 mA cm−2, and an FF of 0.65, yielding a PCE which is ∼38% lower than that of the device based on nanostructured silicon with TMAH treatment. The inferior PV performance is ascribed to the serious surface recombination.37 As shown in Figure 4b, the leakage current of the TMAHtreated nanostructured silicon devices is much lower than that of the untreated silicon devices, suggesting that the junction quality is improved. Furthermore, the JSC of the hybrid devices based on different surface morphologies is consistent with the EQE spectra, as shown in Figure 4c. The device based on ∼14 μm thick planar silicon without TMAH treatment gives a JSC of 18.4 mA cm−2, a VOC of 0.56 V, and an FF of 0.75, achieving a PCE of 7.9%. The previously reported ultrathin planar silicon device with a thickness of 8.6 μm yields a PCE of 5.2%.13 Here, the reduced JSC for the device based on ∼14 μm thick planar
(1)
where S is the surface recombination velocity, W is the wafer thickness, τbulk is the bulk recombination lifetime, and τmeas is the measured minority carrier lifetime. The minority carrier lifetime of the bulk material basically remained constant, so the 21726
DOI: 10.1021/acsami.7b02140 ACS Appl. Mater. Interfaces 2017, 9, 21723−21729
Research Article
ACS Applied Materials & Interfaces
Planar silicon displays the lowest absorption and highest reflection ratio, and the as-prepared nanostructured silicon effectively suppresses the reflection ratio, exhibiting the highest absorption ratio of 85% at 740 nm. After TMAH treatment, an absorption ratio of 77% at 740 nm can be achieved, which is still much higher than that for the initial planar silicon. Crosssectional SEM images of nanostructured silicon treated with TMAH solution are shown in Figure S4. The antireflectivity of the TMAH-treated nanostructured silicon ensures both adequate light absorption and a low surface recombination velocity, as well as good contact with the PEDOT:PSS layer, which is crucial to achieve a high PV performance. Recently, a new technique has been applied to significantly improve the interface between SiNHs and PEDOT:PSS mixed with the cosolvent DMSO, leading to good contact between the polymer and silicon, which could also be introduced during device fabrication.39 We also calculate the Yablonovitch absorption limit for the 14 μm thick substrate by assuming perfect antireflection and perfect light trapping.32 The absorption limit sets an upper boundary for the light absorption in silicon. As shown in Figure 4e, the absorption is dramatically increased across the entire wavelength band when approaching the limit, due to antireflection and light trapping by the Si nanostructures. It is expected that the gap between the absorption and Yablonovitch absorption limits would be minimized through further optimization of the nanostructures.40,41 Transient photovoltage decay measurements are carried out to investigate the charge recombination in nanostructured silicon devices with or without TMAH treatment. The transient photovoltage decay of a solar cell provides direct evidence of the internal charge carrier recombination processes.42,43 Once the steady white bias light is illuminated on a PV device, a certain VOC is generated across the heterojunction. Once the light is turned off, the charge carriers remaining in the device recombine at a certain speed, leading to transient decay of the photovoltage. By recording the transient photocurrent decay simultaneously, the capacitance (C) and charge-carrier concentration (N) trapped by the defect sites in the heterojunction could be estimated.42−44 Detailed calculation methods for C and N are provided in the Supporting Information. C and N are plotted as a function of VOC for devices based on nanostructured silicon with or without TMAH treatment in Figure 5a,b, respectively. It can be found that the devices based on nanostructured silicon with or without TMAH treatment displayed different capacitances at the same photovoltage, which indicates different charge extraction capabilities. The device based on the TMAHtreated nanostructured silicon substrates gives a smaller capacitance than that of the device without TMAH treatment,
Figure 4. Electric-output characteristics of the PEDOT:PSS/Si devices under different surface conditions. (a) J−V curves under illumination at 100 mW cm−2, (b) J−V curves in the dark, and (c) EQE spectra of devices based on silicon substrates with a planar surface (black), an asprepared nanostructured silicon surface (red), and a TMAH-treated nanostructured silicon surface (blue). (d) Schematic device structure of the flexible PEDOT:PSS/Si hybrid solar cell. (e) Absorption spectra of silicon substrates with a planar surface, an as-prepared nanostructured silicon surface, a TMAH-treated nanostructured silicon surface, and upon Yablonovitch limit simulation.
silicon is ascribed to the high light reflection of the planar silicon surfaces, which resulted in poor light absorption compared to that of a thicker device. In comparison with planar devices, nanostructured silicon solar cells exhibit a larger JSC value, indicating that the incident light could be effectively absorbed by nanostructured silicon. The absorption and reflection spectra of the planar and nanostructured silicon with or without TMAH treatment are shown in Figures 4e and S3. According to the absorption spectra, the nanostructured silicon exhibits an obviously better light absorption over a broad spectrum from the visible to the near-infrared range compared to that of planar silicon. The reflection spectra are recorded using a spectrophotometer with an integrating sphere.
Table 1. Electric-Output Characteristics of the Devices Based on (a) Planar Silicon, (b) As-Prepared Nanostructured Silicon, and (c) TMAH-Treated Nanostructured Silicona devices planar Si nanostructured silicon without TMAH nanostructured silicon with TMAH
a
VOC (V)
JSC (mA cm−2)
FF
PCE (%)
0.56 0.55 (±0.01) 0.51 0.50 (±0.01) 0.56 0.55 (±0.01)
18.4 18.4 (±0.0) 19.9 19.6 (±0.3) 21.3 21.0 (±0.3)
0.75 0.74 (±0.01) 0.65 0.62 (±0.03) 0.76 0.74 (±0.02)
7.9 7.8 (±0.1) 6.6 6.5 (±0.1) 9.1 9.0 (±0.1)
Data and statistics were obtained from at least 10 devices for each type. The numbers in bold are the maximum recorded values. 21727
DOI: 10.1021/acsami.7b02140 ACS Appl. Mater. Interfaces 2017, 9, 21723−21729
Research Article
ACS Applied Materials & Interfaces ORCID
Xuegong Yu: 0000-0002-7566-0332 Shuit-Tong Lee: 0000-0003-1238-9802 Baoquan Sun: 0000-0002-4507-4578 Baohua Jia: 0000-0002-6703-477X Notes
The authors declare no competing financial interest. Figure 5. Typical time-resolved transient decay curves of (a) differential capacitance C and (b) charge-carrier density N at different VOC’s of nanostructured silicon devices with or without TMAH treatment.
4. CONCLUSIONS In summary, an organic-silicon hybrid device based on a ∼14 μm thick silicon substrate with a PCE of 9.1% is demonstrated by a facile silicon surface modification method. Nanostructured silicon fabricated by MACE compensates the poor light absorption of the planar silicon substrate. The light absorption capability is enhanced by 1.6 times from the planar silicon substrate to the nanostructured one. Surface recombination of nanostructured silicon is overwhelmed by solution-processed chemical etching. The minority carrier lifetime is improved from the initial 0.7 μs to 1.3 μs after the surface chemical modification, which dramatically suppresses the surface-charge recombination. These combined strategies result in highperformance hybrid solar cells based on the ultrathin nanostructured silicon substrate. These findings could be potentially employed to further reduce the fabrication cost of silicon solar cells by reducing the consumption of silicon materials and thermal energy.
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REFERENCES
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b02140. Methods for calculating the capacitance and chargecarrier concentration. Additional figures of cross-sectional SEM images for planar silicon with different thicknesses, transmissivity of planar flexible silicon substrates with different thicknesses, reflection of ∼14 μm thick silicon with different surface modifications, cross-sectional view of SEM images of nanostructured silicon treated with TMAH, and tables of the electronic output characteristics of devices based on silicon substrate of various thicknesses (PDF)
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ACKNOWLEDGMENTS
This work was supported by the National Key Research and Development Program of China (2016YFA0202402), the National Natural Science Foundation of China (91333208, 61674108, 61605065), the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), the 111 project, and Collaborative Innovation Center of Suzhou Nano Science and Technology. Baohua Jia acknowledges the financial support from the Australian Research Council under the Discover Project (DP150102972) and support from Horticulture Innovation Australia (RFP VG15038).
indicating that charge extraction is more efficient in the device based on TMAH-treated nanostructured silicon substrate. The device based on nanostructured silicon with TMAH treatment generates a lower N than that of the device without TMAH treatment, suggesting an enhanced charge extraction capability and a lower density of trap states for TMAH-treated nanostructured silicon.
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. Phone: +61 3 9214 4819 (B.S.). *E-mail:
[email protected] (B.J.). 21728
DOI: 10.1021/acsami.7b02140 ACS Appl. Mater. Interfaces 2017, 9, 21723−21729
Research Article
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DOI: 10.1021/acsami.7b02140 ACS Appl. Mater. Interfaces 2017, 9, 21723−21729
