Optical Electric Field Distribution Research Articles

Two-dimensional graphene-plasmonic crystals for all-optical switch applications

The present study experimentally and theoretically demonstrated an all-optical switch based on a two-dimensional plasmonic crystal structure which was covered by a graphene layer. The optical modes in the photonic band gap of the crystal can be tuned due to the surface plasmon resonance of plasmonic crystal and nonlinear Kerr effect of graphene. Therefore, in the present study, the plasmon resonance wavelength was shifted about 10 and 2.1 nm for the transverse electric and the magnetic polarization in 58° incident angle, respectively. To get switching manner, by applying the 1550 nm infrared laser as a pump the electric field was increased due to large Kerr nonlinearity of graphene, $$n_{2} \approx$$ 10−7cm2/W. As a result, refractive index was changed and thus the resonance wavelength of surface plasmon was shifted. In order to confirm the experimental results, Kerr nonlinear effect of graphene, and optical electric field distribution at resonance wavelength have been simulated. Based on the results, this switch had three main advantages such as small size, high tunablitiy, and easier fabrication compared to the other methods, which use defect photonic crystal structures.

High response organic UV-blue photodetector with low operating voltage using chemical vapor deposited poly(p-phenylenevinylene)

Abstract High response UV-blue photodiodes are fabricated with chemical vapor deposited poly(p-phenylenevinylene) (PPV) as donor and thermally evaporated C60 as acceptor. Chemical vapor deposition (CVD) has the advantage that scaling up for deposition on large area substrates is feasible. High efficiency is achieved by optimizing the device structure using the optical electric field distribution calculated from transfer matrix simulations. The photodiode operates in the 330 nm to 500 nm wavelength range (UV-A and blue) with a peak responsivity of 148 mA/W at 370 nm and 180 mA/W at 450 nm under a low bias of -1.5 V. A comparison between the photodiodes of CVD grown PPV with spin coated PPV shows that growth by CVD results in significant improvement in responsivity. The high responsivity is attributed to the optimized device geometry and enhanced hole mobility in CVD grown PPV.

Fine Tuning the Light Distribution within the Photoactive Layer by Both Solution‐Processed Anode and Cathode Interlayers for High Performance Polymer Solar Cells

Light management is important for improving light absorption within active layers in polymer solar cells (PSCs). Electrode buffer layers play an important role in modulating the distribution of optical electric filed within the photoactive layer. Herein, the authors employ solution‐processed WOx or ReOx to substitute the acidic poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the anode buffer layer and ZrAcac or HfAcac to replace Mg as the cathode buffer layer. Optical transfer matrix formalism simulation is used to model the absorption spectra, exciton generation rate, and optical electric field distribution of devices. Simulated results shows that stronger absorption, quicker exciton generation rate, and more reasonable photoelectric field distribution can be achieved in the photoactive layer with solution‐processed buffer layer modification, which results in a higher short‐circuit current density (Jsc). Under the guidance of theoretical simulation, the device with architecture of ITO/WOx/PTB7‐Th:PC71BM/HfAcac/Al is optimized. Compared with the traditional PEDOT:PSS‐Mg based device, the Jsc is increased from 16.60 to 18.61 mA cm−2 and the best power conversion efficiency (PCE) is increased from 9.02% to 10.60% for the device with WOx‐HfAcac modification, which is among the best values reported for fullerene‐based PSCs. The good agreement between simulated and experimental results indicates that optical model is a useful tool for device design and optimization.

Low dark-current and high-photodetectivity transparent organic ultraviolet photodetector by using polymer-modified ZnO as the electron transfer layer.

In this Letter, a transparent organic photodetector (OPD) with a property of ultraviolet sensitivity is demonstrated by using an inverted architecture. A conjugated polymer of ploy [(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl)fluorene)] is introduced to modify the energy level and morphology between ZnO and organic optoelectronic material. As a result, at a wavelength of 350nm and a bias of -1 V, the photodetectivity of 1012 Jones from both sides of the transparent device is obtained with a working area of 1 cm2. Moreover, an optical simulation is applied to analyze the optical electric field distribution inside the OPD.

FTO-free top-illuminated colloidal quantum dot photovoltaics: Enhanced electro-optics in devices

A solar cell device architecture with top-illumination, where the light does not pass through the substrate, is advantageous for many applications. It is also specifically useful for the construction of tandem or multiple junction photovoltaic devices, with illumination through the top solar cell. Here, a top-illuminated colloidal quantum dot solar cell (TI-CQDSC) is demonstrated and compared with a conventional colloidal quantum dot solar cell (C-CQDSC) constructed on a FTO (fluorine doped tin oxide) glass substrate both theoretically and experimentally. The optical electric field distribution in the solar cells with different configuration is simulated using transfer matrix formalism and a more intense optical electric field was observed in TI-CQDSC, leading to a higher exciton generation rate within the colloidal quantum dot solid. The TI-CQDSCs are constructed on both nonconductive glass and flexible substrates, and a maximum power conversion efficiency of 6.4% and 5.6% is achieved, respectively, comparing to that of 5.9% for the C-CQDSC. The improved performance of the top illuminated solar cell is attributed to a combination of enhanced optical electric field intensity in the colloidal quantum dot solid and superior conductivity of the transparent metal film electrode.

Improved Optical Field Distribution and Charge Extraction through an Interlayer of Carbon Nanospheres in Polymer Solar Cells

Nanostructured carbon is a low-cost, economic, and elementally abundant candidate for manufacturing high-conductivity counter electrodes of organic photoelectric devices. Herein, we prepare onion-like carbon nanosphere:silver (OLCNS:Ag) composite electrodes for efficient, inverted-architecture polymer solar cells (PSCs) via a simple, solution-processed approach. The optical electric field distribution from the OLCNS:Ag nanocomposite layer opens up the possibility of additional light harvesting of the entire visible spectrum resulting from synergies between both components. The large effective specific surface area and high conductivity of OLCNS allow significant charge transfer and collection, resulting in a remarkably enhanced power conversion efficiency (PCE) of 9.81% in PTB7:PC71BM PSCs and 6.95% in PCDTBT:PC71BM PSCs, compared with control devices with PCEs of 7.76 and 5.31%, respectively. These consequences indicate that OLCNS:Ag composite electrodes constitute a valid and versatile method for realiz...

Dry-Deposited Transparent Carbon Nanotube Film as Front Electrode in Colloidal Quantum Dot Solar Cells.

Single-walled carbon nanotubes (SWCNTs) show great potential as an alternative material for front electrodes in photovoltaic applications, especially for flexible devices. In this work, a press-transferred transparent SWCNT film was utilized as front electrode for colloidal quantum dot solar cells (CQDSCs). The solar cells were fabricated on both glass and flexible substrates, and maximum power conversion efficiencies of 5.5 and 5.6 %, respectively, were achieved, which corresponds to 90 and 92 % of an indium-doped tin oxide (ITO)-based device (6.1 %). The SWCNTs are therefore a very good alternative to the ITO-based electrodes especially for flexible solar cells. The optical electric field distribution and optical losses within the devices were simulated theoretically and the results agree with the experimental results. With the optical simulations that were performed it may also be possible to enhance the photovoltaic performance of SWCNT-based solar cells even further by optimizing the device configuration or by using additional optical active layers, thus reducing light reflection of the device and increasing light absorption in the quantum dot layer.

Understanding the role of thickness and morphology of the constituent layers on the performance of inverted organic solar cells

Inverted bulk heterojunction organic solar cells have generated significant interest in organic photovoltaic research due to much improved life times. Efficiency maximization for a given polymer–acceptor blend requires control of thickness and morphology of various constituent layers. In this manuscript, we present our results on the thickness variation of various constituent layers, viz. ZnO (electron transport layer), blend layer of poly(3-hexyl thiophene) and [6,6]-phenyl-C61 butyric acid methyl ester (active layer) and MoO3 (hole extraction layer) vis-à-vis effect of morphology of layers and optical field distribution on the electrical performance of inverted organic solar cells. The peak performance of the devices occurs for 30nm thick ZnO films, 100nm thick active layer and 10nm of MoO3 layers with an average power conversion efficiency of approximately 3.2% and a fill factor of 61%. The maximization of the device performance upon thickness variation of device constituents appears to result from the combined effects of morphology and the optical electric field distribution in the active layer.

Semitransparent inverted polymer solar cells using MoO 3/Ag/V 2O 5 as transparent anodes

We demonstrate semitransparent inverted polymer solar cells with highly transparent anodes. The structure of the anode is molybdenum trioxide (MoO 3)/silver (Ag)/vanadium pentoxide (V 2O 5). The inner MoO 3 layer is introduced as a buffer layer to improve holes collection, while the outer V 2O 5 layer served as a light coupling layer to enhance optical transmittance of the photovoltaic device. The maximum transmittance of 90% from 400 nm to 700 nm is obtained when the thickness of V 2O 5 is 40 nm. When the thickness of V 2O 5 is 40 nm, under AM1.5G illumination of 100 mW/cm 2 illuminated from ITO side (bottom), the J sc is 5.01 mA/cm 2, the V oc is 0.591 V, the FF is 61.8%, and the PCE is 1.83%; from MoO 3/Ag/V 2O 5 side (top), the J sc is 4.28 mA/cm 2, the V oc is 0.585 V, the FF is 61.9%, and the PCE is 1.55%. The trend of the optical electric field distribution is highly consistent with the J sc , which is dependent on the thickness of the V 2O 5 top capping layer.

Modeling photocurrent action spectra of photovoltaic devices based on organic thin films

We have modeled experimental short-circuit photocurrent action spectra of poly(3-(4′-(1″,4″,7″-trioxaoctyl)phenyl)thiophene) (PEOPT)/fullerene (C60) thin film heterojunction photovoltaic devices. Modeling was based on the assumption that the photocurrent generation process is the result of the creation and diffusion of photogenerated species (excitons), which are dissociated by charge transfer at the PEOPT/C60 interface. The internal optical electric field distribution inside the devices was calculated with the use of complex indices of refraction and layer thickness of the materials as determined by spectroscopic ellipsometry. Contributions to the photocurrent from optical absorption in polymer and fullerene layers were both necessary to model the experimental photocurrent action spectra. We obtained values for the exciton diffusion range of 4.7 and 7.7 nm for PEOPT and C60, respectively. The calculated internal optical electric field distribution and resulting photocurrent action spectra were used in order to study the influence of the geometrical structure with respect to the efficiency of the thin film devices. In this way the photocurrent was optimized.

Enhanced photo conversion efficiency utilizing interference inside organic heteroj unction photovoltaic devices

We study the optical electric field distribution inside heterojunction photovoltaic devices. The generation of excitons and thereby the charge generation is directly dependent of the exciting optical electric field. From calculations of the internal optical electric field distribution we can derive an optimized geometrical structure with respect to the efficiency of this type of devices.