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Inverted device architectures in perovskite research were promising for faster commercialization given the simple processing routes and choice of hole transport materials such as PEDOT:PSS. However, the crystallization of perovskite on the PEDOT:PSS surface led to large domains with several grain boundaries and defects, especially when multi cation systems are involved. Defects formed on the surface of the perovskite are significant reasons for non-radiative recombination, which then limits the performance of the device. Surface passivation of the perovskites through the introduction of large cations was shown as a viable option to minimize the defects and promote better charge carrier extraction. In this regard, recent research was mostly limited to planar architectures and on perovskites prepared on mesoporous TiO2 films. In this work, we report the deposition of guanidinium iodide (GUAI) on the triple cation FAMAC perovskite prepared on a PEDOT:PSS surface in an inverted architecture as a means to induce passivation and suppress non-radiative recombination. We examine the effects of adding different concentrations of GUAI dissolved in isopropyl alcohol as a post-treatment process on triple cation perovskites. The passivation effect led to an increase in open-circuit voltages from 0.89 V to over 0.96 V, which resulted in high efficiency of 16.03% for a GUAI loaded device compared to 12.92% for the control device. The stability was also found to be improved for GUAI passivated devices compared to a control device when tested over 600 hours of storage in ambient conditions.

Inverted-structure perovskite devices with PEDOT and PEDOT/CuI as hole transport layers (HTLs) were prepared on Glass/ITO substrates. Surface morphology observation of the CuI revealed that the CuI grew on PEDOT in island mode. A concentration of 20 mg/ml was necessary for continuous CuI formation on the PEDOT. Optimization of the annealing time and the concentration of CuI precursor solution led to a PCE of 16.5% for a device with PEDOT/CuI as HTL, which was slightly higher than that (15%) with PEDOT as HTL. The slight enhancement of PCE was due to the faster hole transport efficiency and improved light-harvesting in the visible light region. Additionally, the photostability of the devices was greatly enhanced by the insertion of the CuI layer. Analysis indicated that the insertion of the CuI decreased the transmittance of light with wavelengths within 320–410 nm, which was the main reason for the enhanced photostability.

In this investigation, urea (NH2CONH2) was added into the perovskite precursor solution with Pb(CH3COO)3 as precursor. The effects of the urea content in the solution on the crystallization dynamics and the orientation of the perovskite films, and their photovoltaic properties were investigated. The results showed that the optimal annealing duration for the perovskite film increased with the urea content in the solution. An interaction between the urea and the source materials was observed. As a result, urea addition in the Pb(CH3COO)3 based solution has an effect on the crystallization rate and the grain size of the perovskite phase. We found that the suitable amount of urea in the solution was beneficial for the formation of highly (110)-oriented perovskite films and this resulted in the corresponding solar cells with enhanced power conversion efficiency of nearly 17%.

In March of 2018, about 500,000 desktop computers were infected with cryptocurrency mining malware in less than 24 hours. In addition to attacking desktop computers, malware also attacks laptops, tablets, mobile phones. That is, any device connected via the Internet, or a network is at risk of being attacked. In recent years, mobile phones have become extremely popular that places them as a big target of malware infections. In this study, the effectiveness of treatment for infected mobile devices is examined using compartmental modeling. Many studies have considered malware infections which also include treatment effectiveness. However, in this study we examine the treatment effectiveness of mobile devices based on the type of malware infections accrued (hostile or malicious malware). This model considers six classes of mobile devices based on their epidemiological status: susceptible, exposed, infected by hostile malware, infected by malicious malware, quarantined, and recovered. The malware reproduction number, RM, was identied to discover the threshold values for the dynamics of malware infections to become both prevalent or absent among mobile devices. Numerical simulations of the model give insights of various strategies that can be implemented to control malware epidemic in a mobile network.

In this research, we examined the impact of solution concentration on the photovoltaic and the material properties of perovskite solar cells (PSCs) obtained from dehydrated Pb-acetate precursors. The perovskite solution was deposited by a one-step spin-coating technique followed by 5 min of thermal annealing on a hotplate at the temperature of 90 °C to form the perovskite active layer. The PSC device structure adopted was the inverted planar architecture. The precursor solution concentrations were varied from 0.7 to 1.1M, with the optimal solution concentration found to be 1.0M. This concentration results in a power conversion efficiency of 12.2%, an open circuit voltage (Voc) of 0.94 V, a short circuit photocurrent density (Jsc) of 20.71 mA/cm2, and a fill factor of 62.69%. Our investigations revealed that the precursor solution concentration had a huge effect on the quality of the perovskite film and the photovoltaic properties of the PSCs.

Perovskite solar cells have evolved significantly since their inception. However, stability is still a major concern. We fabricated devices using a glass/IT0/PED0T:PSS/MAPbl3/PCBM/Ag device configuration. Devices fabricated using the Pb-acetate precursors showed an efficiency of 13%. This work reports the effect of adding excess lead to the precursor and its impact on the light-induced degradation of efficiency. It is found that 5% excess lead is best for devices regarding the performance and stability and devices retained greater than 50% of the initial efficiency after 2 h of prolonged irradiation. We attribute this phenomenon to the formation of Pbl2 which induces passivation in the grain-boundaries.

In this study of the fabricated perovskite solar cells, flowing nitrogen is introduced during the spin coating of the precursor to remove the solvent vapor. The precursor is then aged prior to the anneal to obtain a pinhole-free perovskite film. Both the nitrogen flow and precursor aging methods resulted in improved film quality. The phase composition and orientation of the CH3NH3PbI3 phase was tuned through control of the aging time. This lead to high-performance CH3NH3PbI3 planar perovskite solar cells with power conversion efficiency over 16%. The intermediate phase composition was sensitive to the ambient atmosphere. The content of the PbI2 in the final CH3NH3PbI3 films varied with precursor aging time. The combination of nitrogen flow and suitable aging time resulted in films with enhanced (110)-orientation, compactness, charge carrier lifetimes, and correspondingly power conversion efficiencies.

In this study, we reported a low-temperature, one-step solution process to fabricate perovskite solar cells using dehydrated lead acetate as the lead source. These perovskite films were aged at 200 s before thermal annealing at 90 °C for 5 min. Uniform perovskite films with lesser pinholes were obtained by this technique. The inverted planar (n-i-p) perovskite solar cell device resulted in a power conversion efficiency of 13%. A substantial finding was that the devices demonstrated high reproducibility. We also investigated the effect of annealing temperature on the optical and structural properties of the films and on the photovoltaic performances of the fabricated solar cell devices. For the aforementioned, a low-temperature, one-step solution process, the optimal temperature was achieved at 90 °C.

The stability of perovskite solar cells exposed to prolonged solar irradiation is a major concern that has not been thoroughly investigated in the past. In this investigation, devices fabricated with the architecture, glass/ITO/PEDOT:PSS/MAPbI3/PCBM/Ag using Pb acetate as a source material, were found to operate with an efficiency of about 13%. Adding excess amounts of Pb to the precursor resulted in a presence of Pb in the perovskite (PVS) active layer. In addition, the impact of photo-induced degradation on the device efficiency was investigated. X-ray Diffraction and Time-resolved Photoluminescence analyses were used to evaluate the impact of excess Pb before and after illumination. The results indicate that changes in the crystallinity occur without any significant decrease in charge carrier lifetimes, and this is attributed to the formation of the degradation product, PbI2. This by-product has been shown to have beneficial effects due to its influence in passivating grain boundaries and in altering the band structure at the interface between the active layer and the electron transport layer. This work demonstrates that 5 mol% excess Pb is the optimal concentration with respect to efficiency and stability of these devices. The devices can retain more than 50% of their initial efficiency after 1 h of simulated solar exposure, when compared to 0 mol% and 10 mol% excess Pb samples.

The influence of the content of trifluoroacetate (TFA), in the precursor solution, on the critical current density (Jc) of YBa2Cu3O7−x (YBCO) superconducting films was investigated. We found that a TFA/Ba ratio of 0.68 is optimal to obtain high-performance YBCO films. Using this optimal solution, we then developed an ultraviolet (UV) light soaking technique to prepare YBCO films. This resulted in the constituent elements being uniformly distributed in the films, and this then enabled enhanced Jc. The addition of water vapor during the UV soaking process decreased the content of carbon residue in the films, and further increased the Jc of the resulting YBCO films.

The existence of the Schottky barriers at the top and bottom electrodes of the ferroelectric thin film sandwich structure makes it difficult to separate and collect electron-hole pairs, thus limiting the enhancement of the photocurrent. In this paper, Pb(Zr,Ti)O3 (PZT) and composite structure of PZT/CuO films are prepared by a sol-gel method and their photovoltaic properties have been investigated. It is found that the PZT/CuO films show a short circuit photocurrent density (JSC) enhanced by nearly 6 times and power conversion efficiency (PCE) increased by six-fold when compared to those of the PZT film. The increase of photovoltaic response is due to the internal electric field of PZT/CuO p–n junction, which plays an important role in driving the photo-generated carriers. The Ohmic contact between the interfaces of LNO/PZT and CuO/Pt also reduce the resistance of the transportation of photogenerated carriers. Furthermore, the JSC of PZT/CuO film are observed to be 0.03 and 0.013 mA/cm2 after upward poling and downward poling, respectively, indicating that the photocurrent can be modulated by the direction of the polarization electric field. The photovoltaic effect of composite films and its potential mechanism are also explored. This work provides an efficient approach to develop ferroelectric film based on photovoltaic devices.

Control of the nucleation and growth of the CH3NH3PbI3 (MAPbI3) phase is one of the important issues in the development of the high-performance MAPbI3 perovskite solar cells. In this work, we demon...

Transparent composite electrodes (TCE), TiO2/Ag/TiO2 (TAgT), have been demonstrated as a promising alternative of indium tin oxide (ITO) in organic solar cell application. TiO2/Ag/TiO2 have been incorporated into bulk heterojunction organic solar cells (OSCs) to replace ITO as the anode. Two different hole transfer layers (HTL), poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) and MoO3, are compared in terms of their compatibility with the TiO2/Ag/TiO2 anode. The MoO3 layer has been shown to be a beneficial HTL for TiO2/Ag/TiO2 based OSC. However, the wettability of MoO3 for polymer blend is not as good as PEDOT:PSS, and results in a relatively thin active layer in OSCs. On the other hand, ITO based OSCs using PEDOT:PSS and MoO3 as the HTL are fabricated as control samples to compare the performance of TAgT and ITO anodes. Results of the investigation shows that the superior electrical property of TAgT anodes contributes to the effective collection of photo-carriers and its lower optical transmittance barely degrades the light absorption in OSCs. In a few words, the higher Haacke figure of merit of TAgT enables better performance of OSCs with MoO3 HTL, in comparison with ITO based OSC.

Organic–inorganic CH3NH3PbI3 (MAPbI3) inverted structured perovskite films were prepared using Pb(CH3COO)2 (Pb(OAc)2) and CH3NH3I (MAI) as source materials. The structural, optical and photoelectronic properties of the MAPbI3 films varied with the Pb(OAc)2/MAI molar ratio. It was found that the Pb(OAc)2/MAI molar ratio greatly influenced the structure and morphology of the MAPbI3 films. A suitable amount of excessive Pb(OAc)2 (about 5 mol% excessive Pb) in the solution made the film smoother with improved film crystallinity. This resulted in enhanced power conversion efficiency (PCE). However, for films derived from solution with low Pb(OAc)2/MAI or high Pb(OAc)2/MAI ratio, defects such as pits or pinholes were easily formed with low crystallinity, and hence decreased the lifetime of the carriers and photoelectrical properties of the final solar cells. Using a solution with 5% excessive Pb, inverted structured CH3NH3PbI3 perovskite solar cells with PCE of nearly 14% were obtained.

A novel ultraviolet photochemical method was used to prepare TiO2 resistive-switching films. Amorphous TiO2 films were formed on flexible indium-tin oxide (ITO) coated polyethylene terephthalate (PET) substrates by deep ultraviolet irradiation at 150 °C. A Pt/TiO2/ITO/PET device was then fabricated to investigate bipolar resistive switching of the films for potential application in non-volatile memories. The ratio of on-state to off-state currents was measured, and a good value of 1000 was obtained. The retention and switch-cycling characteristics of the device were investigated for different bending radii. The resistive switching behavior of the flexible device remained stable after 600 cycles of electrical switching and 1000 cycles of bending.

The efficiency of more than 25% in organic-inorganic hybrid perovskite solar cells has made them very attractive in the pursuit of cheaper alternatives to Si-based devices. However, the stability of the perovskite solar cells was challenging, given their high susceptibility to moisture. Very few reports have emerged in this regard that investigated the influence of introducing large cations into a triple cation perovskite (TC-PVS), with several studies limited to single and dual cation perovskites. Further, the crystallization of TC-PVS on a polymer surface such as PEDOT is not straightforward, and their inclusion in inverted solar cell devices was limited. In this work, we investigated the impact of incorporating Phenyl ethyl ammonium cation into FAMACs triple cation composition. We demonstrated improvements in the crystallinity and more uniform coverage with little to no pinholes and smooth morphology for an optimum PEA amount of 1.67% in the precursor solution. The superior morphology, along with a passivation effect from a quasi 2D phase, led to increased photoluminescence and minority carrier lifetimes. Corresponding inverted photovoltaic devices prepared with PEA showed increased open-circuit voltage from 0.89 V for a control sample to 0.95 V for 1.67% PEA and 0.98 V for 5% PEA, doped devices in an inverted configuration. The efficiency, as a result, increased from 11.27% for a control device to 14.85% for a 1.67% PEA doped device. Further, PEA doped devices showed improved operational and thermal stability attributed to the higher moisture tolerance and light-soaking ability of the PEA doped TC-PVS compared to the undoped TC-PVS.

As a promising indium-free electrode, transparent composite electrode (TCE) TiO 2 /Ag/TiO 2 is an attractive alternative to indium tin oxide (ITO). The multilayer structure of TiO 2 /Ag/TiO 2 is deposited on glass substrate by room-temperature sputtering. The effects of deposition rate, thickness of Ag and TiO 2 layers on the electrical and optical properties of this TCE are presented. Results show that the Ag films tend to have fewer voids to form, if the Ag deposition rate is sufficiently high. The presence of fewer voids in the Ag layer results in higher transmittance and lower sheet resistance of the corresponding TiO 2 /Ag/TiO 2 structure. In order to increase the solar input to the P 3 HT:PC 61 BM organic solar cell, the layer thicknesses of TiO 2 /Ag/TiO 2 electrodes are theoretically and then experimentally optimized, such that its optical transmittances are maximized across the wavelength range where the light absorption of P 3 HT:PC 61 BM is highest. In this study, the device-specific Haacke figure of merit (FOM) of the TiO 2 /Ag/TiO 2 electrode is optimal with the use of 42 nm TiO 2 layers and 10 nm Ag layer. This optimal Haacke FOM is two times higher than that of ITO electrodes. The conventional bulk heterojunction organic solar cell (OSC) fabricated on optimized TiO 2 /Ag/TiO 2 electrode shows high power conversion efficiency (PCE), almost 100% higher than PCE of OSC fabricated on ITO. Our finding indicates that TiO 2 /Ag/TiO 2 electrode can be specifically tailored to particular applications. It can be implemented in organic solar cell and has considerable potential to replace ITO in solar cell applications.

Silver-chalcogenide glass flexible sensors were tested to study the impact of physical design parameters on the performance characteristics of the sensors in response to ionizing radiation. Results show that by changing lateral spacing between adjacent electrodes, the limit of detection and dynamic range can be regulated. Likewise, by changing the diameter of the electrodes, the sensor high and low resistance states can be adjusted to a desired range. In contrast, the influence of the electrode diameter on the sensor performance characteristics was found to have less of an impact on sensor performance. Mechanisms for ion transport and reactions are investigated using TCAD simulations in which the standard statistics and transport equations for free carriers are simultaneously solved. The simulation results are qualitatively in a good agreement with experimental data.

Electrochromic films have been used as a non-emissive material for display applications. Such materials have already been integrated in antiglare rearview mirrors for passenger vehicles as well as smart windows intended for energy savings for buildings. However, most electrochromic materials are deposited on rigid substrates, which prevent its use in flexible and stretchable electronic applications, where low temperature deposition techniques are desired. Additionally, electrochormics require an external power source to drive the underlying reduction/oxidation reaction. In this work, electrochromic materials inkjet-printed onto flexible and stretchable substrates have been explored. These devices are "self-powered" by organic solar cells also fabricated on flexible and stretchable substrate such as PDMS and PET. A set of inks based on a combination of synthesized and commercially obtained WO_3 nanoparticles, W-TiO_2 and TiO_2 nanoparticles were evaluated. The microstructure of the nanoparticles used in this study were examined under scanning electron microscopy for examining nanoparticle morphology, x-ray diffraction for chemical and structural characterization, and dynamic light scattering for particle size determination. Electrochromic layers were then ink-jet printed on flexible and stretchable PDMS substrates, using synthesized Ag nanowires as conductive, yet highly transparent electrodes. The stretchable printed electrochromic devices under various stress conditions and electrochromic performances were evaluated and demonstrated clear switching behavior under external bias, with 7 second coloration time, 8 second bleaching time, and 0.36-0.75 optical modulation at ?=525 nm. Cyclic voltammetry and galvanostatic charge/discharge measurements demonstrated high areal capacitance, with limited stability upon cycled operation. The electrochromic devices were then integrated in an Internet of Things (IoT)-enabled switching configuration, self-powered by PCDTBT:PC_70BM organic photovoltaics. The bulk heterojunction devices were evaluated with varying hole-transport layers and substrates, and exhibited the strongest performance of PCE? 3%, V_oc=0.9V and J_sc ? 10-15 mA/cm^2. The described self-powered, IoT-enabled, ink-jet printed electrochromic devices, fabricated on flexible substrates, are demonstrative of potential applications for wearable electronics.

A low temperature sol-gel process was used to fabricate zinc-oxide and yttrium-doped zinc oxide layers. These zinc-oxide and yttrium-doped ZnO films were used as electron transport layers in conjunction with P3HT and PC16BM type solar cells. It was demonstrated that annealing and doping of electron transport layer influenced the overall organic solar cells performance. Anneals of ~ 150?C provided the highest device performance. Compared to the undoped zinc oxide, the device with yttrium doped zinc oxide layers showed improved efficiency by about 30%. Furthermore an equivalent circuit was proposed to understand the connection between the electrical and optical characteristics of the device. Comparisons between the simulated and experimental current-voltage(I-V) curves displayed only a 1.2% variation between the curves. Clearly, our experimental and simulated studies provide new insight on the equivalent circuit models for inverted organic solar cells and further improvement on photovoltaic efficiency.

Amorphous indium gallium zinc oxides (IGZO) of 100 nm thickness were deposited onto glass substrates by sputtering at room temperature. The films were subsequently annealed in air, vacuum, forming gas and O2 environments by both conventional and microwave methods. The optical and electrical properties of the as-deposited and annealed samples were measured and compared. It was seen that microwave annealing had a dual advantage of reduced time and lower temperature compared to conventional annealing. The optical and electrical properties of the IGZO thin films were measured by UV–Visible spectrophotometry, Hall measurement and four-point probe analyses, respectively. On microwave anneals of 4 min at 200°C, the resistivity of IGZO thin films was lowered to 4.45 and 4.24 × 10−3 Ω-cm in vacuum and forming gas, respectively. However in conventional annealing at 400°C, it took 24 h to reach 4.5 and 4.2 × 10−3 Ω-cm in vacuum and forming gas, respectively. The average transmittance of IGZO improved from 80% to almost 86% for microwave annealing.

The sensing stability and sensitivity of a molecularly imprinted polymer (MIP) selective to the adsorption of hydrocarbons was studied. The MIP was deposited on a quartz crystal tuning fork (QTF) resonator, whose chemical and physical properties were monitored over time, using Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller adsorption isotherm analysis (BET), and Fourier transform infrared spectroscopy (FTIR). In addition, kinetic binding analysis of the MIP-modified QTF sensor was carried out for the sensors stored and operated under ambient conditions (740 mmHg, 20–23 °C). Although the polymer was able to maintain its physical and chemical properties at microscopic, BET adsorption, and spectroscopic levels, the intrinsic adsorption properties of hydrocarbons onto MIP binding sites altered over time, which suggest that the 3-D conformational changes of the polymer binding sites occurring at nanoscopic/angstrom level may cause the sensitivity degradation in MIP. The changes were significantly reduced by stabilizing the polymer under low storage temperatures.

Carrier recombination lifetime is a key semiconductor parameter that not only has a major role in how a variety of solid-state devices operate, but one that can also be used as a process cleanliness monitoring tool. Lifetime measurement on epitaxial wafers, where the epilayer thickness is smaller than the minority carrier’s diffusion length, has always been a challenging task. Although the pulsed MOS capacitor has been shown to be an eminently suitable technique for measuring the generation lifetime ( $\tau _{g})$ on these wafers, measuring the recombination lifetime ( $\tau _{r})$ yet has remained complicated and difficult to implement. In this paper, a new technique for accurate measurement of $\tau _{r}$ will be presented. Lifetime will be extracted from the capacitance transient ( $C$ – $t$ ) of an inverted MOS device while being excited by an optical pulse. In addition to its easy implementation, the recombination lifetime extracted this way is least affected by Si/SiO2 surface and epi/substrate interface effects when compared with older techniques such as the photoconductance decay. TCAD simulations and experimental results will be presented to demonstrate the promising application of the optically excited MOS to the characterization of p/p+ silicon epitaxial layers.

The compatibility of gold with underlying substrate materials is important for device performance and reliability. Gold nanolayers of various thicknesses (4–14 nm) are deposited onto different substrates (glass and flexible substrate) by sputtering at room temperature. The flexible substrate used in the study was polyethylene napthalate (PEN). The structural and electrical properties of the Au thin films are compared between the two substrates. Contact angle measurements are done to understand the wettability of Au thin films on various substrates. The Au film on PEN showed hydrophobic behavior while the films on glass were distinctly hydrophilic with contact angle of around 50–68.5° against water. The poor wettability is associated with increased roughness of the PEN substrate.

Multilayer structures of TiO2/Au/TiO2 have been deposited onto flexible substrates by room temperature sputtering to develop indium-free transparent composite electrodes (TCEs). The effect of Au thicknesses on optical, electrical properties and the mechanism of conduction have been discussed. The electrical conductivity of the TCEs is solely contributed by the middle metal layer. The critical thickness (t c) of the Au mid-layer to form a continuous conducting layer is 10 nm, and the multilayer has been optimized to obtain a sheet resistance of 12.2 Ω/sq and an average optical transmittance of 86% at 590 nm. The Haacke figure of merit (FOM) for t c has one of the highest FOM with 18 × 10−3 Ω−1. The samples were annealed in various environments for 24 h up to 150°C.

The interest in indium-free transparent composite electrode (TCE), a thin metal layer embedded between two transparent metal oxide (TMO) layers resulting in TMO/metal/TMO composite structure, has grown recently with the advent of their high figures of merit and its potential application in photovoltaic applications. However, most of the work to date has focused on experimentally producing the best optically transmitting TCE. To better design TCEs and minimize experimental work, it would be useful to develop a model that predicts the optical transmission. In the current work, the transfer-matrix method is employed to calculate the transmittance spectrum of TCE. To validate this approach, the transmittance spectra of TiO2/Au/TiO2 and TiO2/Ag/TiO2 multilayer thin-film TCEs are calculated with use of extracted material parameters. The calculated transmittance spectrum of TiO2/Au/TiO2 matches the measured spectrum quite well. However, the calcualted transmittance of TiO2/Ag/TiO2 is higher than its measured transmittance. The presence of voids in the Ag film is probably responsible for the decreased transmittance of the TiO2/Ag/TiO2 sample, and the continuous Au film in TiO2/Au/TiO2 ensures a good agreement between transmittance prediction and measurement. Our approach is a reliable tool to predict the optical transmittance of TCE with continuous films, and it can efficiently expedite the selection from numerous possible combinations of transparent metal oxides and metals when developing TCEs for future photovoltaic applications. It can also serve as a convenient method to assess the continuity of embedded metal layer.

A solution based approach to deposit a p-type CuI hole-transport layer that replaces PEDOT:PSS layer in the fabrication of high-efficiency poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) solar cells is reported here. X-ray diffraction analysis identifies the cubic γ-phase of CuI. A Kelvin probe measurement technique is utilized to identify the effective work function of CuI coated ITO. The device optimization is done by varying the concentration of CuI in the precursor solution which played an important role in the efficiency of the solar cell devices. In an effort to explore new inexpensive hole conducting materials for organic solar cells, we have identified copper iodide as a possible alternative. Moreover, the low temperatures required to process CuI films make it a perfect candidate to be used in organic solar cells on flexible substrates.

aSchool for Engineering of Matter, Transport, and Energy, Arizona State University, Tempe, Arizona 85287, USA bCHD-Fab, Freescale Semiconductor Inc., Tempe, Arizona 85284, USA cKorea Institute of Science and Technology, Seoul, South Korea dSchool of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287, USA eDepartment of Chemical and Materials Engineering, University of Nevada, Reno, Nevada 89557, USA

Zinc-oxide and yttrium-doped ZnO films were fabricated by a sol–gel processing technique and were incorporated as an electron transport layer in inverted organic solar cells (with an active layer comprising a blend of P3HT and PC61BM). First, the annealing conditions for the pure sol–gel ZnO layers were optimized. An interesting observation was that the annealing temperature of the ZnO layer significantly influenced the overall organic solar cells performance. Annealing the ZnO film at temperatures of ∼150 °C provided the highest device performance. The physical and surface properties of these ZnO films were examined by X-ray diffraction, atomic force microscopy and UV-vis transmittance measurements. Utilizing the optimized annealing conditions, we further fabricated high-efficiency organic solar cells by doping yttrium in the zinc-oxide (YZO) electron transport layers. The efficiency of YZO based devices was improved by 30% when compared to that of the undoped zinc oxide based devices.

In this work, a newly fabricated organic solar cell based on a composite of fullerene derivative [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) and regioregular poly (3-hexylthiophene) (P3HT) with an added interfacial layer of AgOx in between the PEDOT:PSS layer and the ITO layer is investigated and an equivalent circuit model is proposed for the device. Incorporation of the AgOx interfacial layer shows an increase in fill factor (by 33%) and power conversion efficiency (by 28%). Moreover, proper correlation has been achieved between the experimental and simulated I-V plots. The simulation shows that device characteristics can be explained with accuracy by the proposed model.

In this paper, previous work on chalcogenide-glass (ChG)-based radiation sensors is extended to include the effects of mechanical strain and temperature stress on sensors formed on a flexible polymer substrate. We demonstrate the feasibility of producing inexpensive flexible radiation sensors, which utilize radiation-induced migration of ${\rm Ag}^{+}$ ions in germanium selenide ( ${\rm Ge}_{20}{\rm Se}_{80}$ ) films to produce a decrease in resistance of several orders of magnitude between surface electrodes. This change in resistance can be related to total ionizing dose to give an instantaneous readout of radiation exposure. The ChG films are inherently flexible and this, along with an extremely simple device fabrication process at or near room temperature, allows inexpensive sensor structures to be fabricated on lightweight pliable polymeric substrates such as polyethylene napthalate (PEN). Test samples were irradiated with ionizing radiation (UV light and $^{60}$ Cobalt gamma rays). Irradiated samples were subjected to both tensile and compressive stress, and elevated operating temperatures. Stress and exposure to increased ambient temperature had little effect on device resistance. Analysis of the experimental data is supported by the results of COMSOL simulations that model radiation-induced lateral Ag diffusion in ChG.

We have investigated the nucleation and growth of single crystal ZnO nanowires on carbon films. ZnO nanostructures were grown on a transmission electron microscopy (TEM) grid consisting of a carbon film supported by a copper frame. No seed layer was used to provide nucleation sites. The resulting ZnO nanowires showed different diameters and lengths for growth on metal versus the carbon film. This is indicative of differences in nucleation and growth processes that depend on the substrate that was used. Our results indicate that ZnO nanowire arrays can be grown on carbon films by using a ZnCl 2 growth solution. This is a simple and low-cost method for growth of the nanowires. The method can also be used for investigating the mechanisms and morphology of ZnO growth on such carbon-based substrates. The growth of ZnO nanowires on carbon films, ribbons or nanodots has potential application for use in sensors, electronic, optoelectronic and photovoltaic devices.

We demonstrate the power conversion efficiency of bulk heterojunction organic solar cells can be enhanced by introducing Ag nanoparticles into organic exciton blocking layer. The Ag nanoparticles were incorporated into the exciton blocking layer by thermal evaporation. Compared with the conventional cathode contact materials such as Al, LiF/Al, devices with Ag nanoparticles incorporated in the exciton blocking layer showed lower series resistances and higher fill factors, leading to a 3.2% power conversion efficiency with a 60 nm active layer; whereas, the conventional devices have only 2.0–2.3% power conversion efficiency. Localized surface plasmon resonances by the Ag nanoparticles and their contribution to photocurrent were also discussed by simulating optical absorptions using a FDTD (finite-difference-time-domain) method.

Highly transparent conductive composite electrodes made of multilayer of TiO2 and Cu (TiO2/Cu/ TiO2) thin films (30/3‐9/30nm thick) are deposited onto flexible substrates at room temperature. The micro-structural, optical and electrical properties of the multilayer are studied with the use of atomic force microscopy, uv-visible spectrophotometry and Hall measurement tool. The Haacke figure of merit (FOM) has been calculated to evaluate the performance of the multilayer films. The highest FOM achieved is 6.4 ×10 −3 � −1 for a Cu thickness of 6 nm with a sheet resistance of 19 � /sq and an average transmittance of 81%.

In this paper we demonstrate the use of self-assembled monolayer modified indium tin oxide (ITO) electrode in bulk heterojunction solar cell structure based on a photoactive layer of poly(3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester (P3HT:PC61BM). The device studies show that there is a significant enhancement in the short-circuit current as well as in the shunt resistance on use of the hexamethyldisilazane (HMDS) layer. The enhancement in short-circuit current density is attributed to the good contact formed between the organic materials and the methyl groups of HMDS. A significant improvement in the external quantum efficiency is also observed in case of the HMDS modified ITO based solar cells.

We demonstrated the use of an additional cathode layer of zirconium acetylacetonate (ZAC) prepared in IPA for Perovskite solar cells (PSC) and achieved a power conversion efficiency of 15.2%, which is about 25% higher when compared to a control device with only PCBM. Our results indicated that IPA was the best alcohol-based solvent to obtain a smooth film and also prevented any corrosion of the underlying layers. We investigated the surface effects of adding the layer and also realized an optimized concentration of 1.5 mg/ml was best for device efficiency as well as reduced the RMS to 3 nm. Dark-current time-resolved photoluminescence measurements were used to understand the effect of the thickness and concentration of the ZAC layer on the performance of the device.

For the first time it is reported that nitrogen-doped titanium oxide with light annealing can improve the device performance by 300% when acting as an interfacial layer between CdSe quantum dot/poly-3-hexylthiophene and the cathode in the photovoltaic devices. Substitutional N doping with a concentration of 1.2 at.% was found by X-ray photoelectron spectroscopy which was responsible for 0.1 eV band gap reduction of TiOx. Photoluminescence and the external quantum efficiency spectrum confirmed the enhanced charge collection and association rate after light annealing. Three-dimensional atomic force microscopy results agreed with the series resistance measurements, confirming that a good contact was achieved. The topography study also indicated that the active layer morphology changed upon light annealing. Improved stability and longer lifetime were also found with TiOxNy capped devices, which were optimized with light annealing. TiOx capped devices were also evaluated for comparison in this study.

Yttrium doped zinc oxide (ZnO) nanowires prepared on seedless indium tin oxide (ITO) substrates were used for nanostructured bulk heterojunction organic solar cells (OSCs). Without patterning by a mask, the optimized areal density of ZnO nanowires decreased the reflection of incident light impinging upon the substrate by more than 50%, resulting in better incident-photon to current efficiencies (IPCEs) than for solar cells without ZnO nanostructures. OSC decorated with yttrium doped ZnO nanostructures showed an increase in current density from 8.9 mA/cm2 to 9.9 mA/cm2 resulting in 15% better device performance than a planar bulk heterojunction OSC. It was found that the antireflective effect due to ZnO nanowires was maximized with an areal density of 50 nanowires per 100 μm2. The areal density was optimized by incorporation of 0.02 mM yttrium chloride into the growth solution during nanostructure formation. In addition, OSC that incorporated the optimized areal density and length of ZnO nanostructures showed a 25% improved power conversion efficiency of 2.5% compared to OSC prepared on an ITO substrate without the ZnO nanostructures. Our results indicate that growth of density-controlled ZnO nanowire arrays on seedless ITO substrates using yttrium dopant is simple, low cost, and easily controllable method that enables low temperature fabrication, without patterning, of antireflective structures for significantly enhanced efficiency bulk heterojunction OSCs.

We report on the electrical and optical properties of ZnO/Ag/MoO 3 (ZAM) multilayer electrodes deposited directly on glass substrates by a combination of radio frequency (RF) and direct current (DC) sputtering for bulk-heterojunction organic solar cells (OSCs). Compared to indium tin oxide (ITO) electrodes showing 20 Ω/sq, the transparent composite electrodes (TCE) in this study exhibited very low sheet resistance of 5 Ω/sq without post annealing. In addition, as a hole transport layer, the MoO 3 performed with a higher fill factor than PEDOT:PSS due to lower series resistance, resulting in a power conversion efficiency of 2.3%, V oc of 0.59 V, and J sc of 9 mA/cm 2 . The power conversion efficiency of the OSC with the ZAM electrode is lower than that of organic solar cells on ITO which has 3.3% efficiency, due to lower transmittance after MoO 3 layer deposition. However, our results do support the possibility of using MoO 3 as both Ag protecting and hole transport layers for indium-less and PEDOT:PSS-less bulk-heterojunction OSCs.

We develop a modified pulsed MOS technique for measuring generation lifetime in ultraclean and thin p/p+ epitaxial layers, which can be used to detect metallic impurities with densities as low as 1010cm-3. The widely used classic version is shown to be unable to effectively detect such low impurity densities because of the domination of surface generation; whereas, recombination lifetime measurement techniques have serious limitations for layers that have smaller thicknesses than the minority carrier diffusion length.

Stability testing of indium-zinc oxide under extreme conditions is necessary before the metal oxide can be deemed a reliable alternative to a-Si as channel layer in thin film transistors (TFTs). In this paper, we apply thermal stress under positive and negative gate bias stress creating practical application conditions. This stress scenario gives greater insight into thermally activated defects in the presence of an electrical field. Operational temperatures of 20 °C, 50 °C, and 80 °C are used, and a more rapid degradation of the devices is seen with increased temperatures. Kink and dip are observed due to the donor-like trapped charges increasing the subthreshold swing and acceptor-like trapped charges reducing the ON current, respectively. Post fabrication, long-time anneals for 12-, 24-, 36-, 48-, and 60-h at low temperatures (150 °C) are performed to alleviate defects. The 48-h annealed TFTs show remarkable stability under extreme temperatures and electric fields maintaining a high ON-OFF ratio (~108) after 104 s. This is attributed to the reduced density of charges in acceptor-like trap states, modeled to reduce by 58% from a 12-h anneal and to insignificant extent over a 48-h anneal.

This study reports the operational instability and failure causing defect mechanisms of indium gallium zinc oxides based thin film transistors (TFTs) under practical, combined bias and illumination stress conditions. The effect of the illumination stress with light source of different wavelengths (410 nm, 467 nm, 532 nm, and 632 nm) has been explained. Wavelengths shorter than green light (532 nm) demonstrate creation of ionized vacancies and subsequent generation of excess carriers that alter TFT functions. Recovery evaluations performed upon removal of combinatory stresses exhibits incomplete recovery due to incapacity in regenerating neutral oxygen vacancies. The Ion/Ioff values show an increase by an order of magnitude when compared to previous studies where the Ion/Ioff is reduced. This can be contributed to the reduced defect and vacancy densities due to the effective post anneal process.

This study discusses thermally activated defects in the channel layer of indium zinc oxide (IZO) thin film transistors (TFTs) under electrical and thermal stress resembling practical stress scenarios. Operating temperatures of 20, 50, and 80 {degree sign}C have been chosen to establish a relation between temperature and failure mechanism. With increasing stress period, acceptor- and donor-like traps contribute towards degrading drain current and subthreshold swing. Low temperature long hour anneal for 12, 24, 36, 48 and 60 hr at 150 {degree sign}C are performed on the TFTs post fabrication to cure the defects formed during fabrication. Structures treated for 48 hr demonstrate high stability under extended kinetic stresses, maintaining a high transistor Ion/Ioff ratio of ~ 108. A physically-based mathematical model discusses the reduction in the density of acceptor-like trap states by 50 % for TFTs treated for 12 hrs, and to insignificant numbers for TFTs treated for 48 hr.