87 research outputs found
Application of UV-filtering Down-conversion Layer on Flexible Organic Solar Cells
No full textOrganic photodiodes (OPDs) have recently been studied for various applications such as organic image sensors, bio-inspired artificial eyes, and wearable bio sensors. By taking advantage of tunable optical properties, large-area scalability, and mechanical flexibility of organic electronic materials [1-4], OPD-based image sensors may be beneficial in large-sized or bendable image sensors that can be coupled with displays in various form factors. In particular, the need of near-infrared (NIR) organic photodiodes is growing as it can be useful for detection of clear images under low-light conditions (e.g. face recognition in dark) or for detection of various biosignals (e.g. veinimaging based identification, or pulse oximetry data). To fully utilize the potential of NIR organic photodiodes, however, the external quantum efficiency (EQE) and simplicity in fabrication need to be improved further to match the requirements for many of the applications.
The aim of this study is to fabricate NIR organic photodiodes and improve EQE in a simple manner compatible with the existing infrastructure and common process. In this regard, we adopt common solution-processed organic donor-acceptor blendsand try to exploit their charge-transfer (CT) absorption band in the NIR region. On top of that, the microcavity effect is applied to compensate a relatively low CT absorption in the NIR region to improve EQE. Upon optimization, we demonstrate approximately ten-fold increase in EQE from 1.16% to 10.60% in the wavelength of 985 nm, illustrating that the proposed approach holds a great promise in detecting NIR photons with relatively long wavelength at high efficiency
Embedded UV Down-Conversion Layer for Organic Solar Cells with Improved Performance and Stability
No full textHigh-energy photons arising from the UV component of the solar spectrum are considered as a primary cause of photoinduced degradation observed in organic solar cells (OSCs). We herein demonstrate the scheme of harvesting these high-energy photons via a UV down-conversion (UVDC) layer embedded in thin polymeric substrates as an effective strategy for simultaneously enhancing efficiency and improving the photostability of OSCs. Transparent UV-curable photopolymer resin (NOA 61, Norland, Inc.) is employed to prepare a polymer substrate and to sandwich the UVDC layer comprised of Ir(dmppy-ph)2tmd-a highly efficient yellow phosphorescent emitter, which exhibits a high degree of spectral overlap between its emission spectra and the absorption spectra of the PM6, a donor polymer used to prepare photoactive blend along with non-fullerene acceptor Y7. The PM6:Y7 bulk heterojunction OSCs fabricated on the substrates with the UVDC layer are found to show a nearly 7.2% higher power conversion efficiency (PCE). The study reveals that observed improvement in performance is essentially due to the ability of the UVDC layer to absorb some high-energy photons and make them available for absorption by the photoactive layer by down-converting them to photons in the visible region and due to the optical scattering effect that leads to a longer effective optical path length within the active layer. A study done by monitoring the PV performance as a function of UV exposure time indicates that, with the proposed UVDC approach, it is possible to achieve nearly a 3-fold enhancement in T 97, or the time it takes for PCE to become 97% of the initial value, by alleviating the UV-induced photochemical degradation. Statistical analysis is also performed for the wide range of sample distributions, verifying the reliability and repeatability of the results.
Impact of non-fullerene acceptors and solvent additive on the nanomorphology, device performance, and photostability of PTB7-Th polymer based organic solar cells
No full textNon-fullerene acceptors have recently ignited extensive interest in organic solar cells (OSCs) because of their higher power conversion efficiency (PCE) than their fullerene counterparts. Though the effect of solvent additive 1, 8-diiodooctane (DIO) has been studied extensively for fullerene-based acceptor OSCs, not much is known for non-fullerene acceptors OSCs. In our work, bulk-heterojunction (BHJ) OSCs were fabricated by blending fullerene (PC71BM) and non-fullerene (ITIC and IEICO-4F) acceptors with low bandgap polymer donor (PTB7-Th). Further, the effects of non-fullerene acceptors on the nanomorphology, performance, and photostability of the devices were investigated. In the absence of DIO, devices with IEICO-4F acceptor showed higher PCE than PTB7-Th: ITIC and PTB7-Th: PC71BM BHJ-OSCs due to their absorption in near infrared along with high J (sc). The addition of DIO increased PCE in PTB7-Th: PC71BM BHJ-OSCs due to improved miscibility of fullerene molecules, higher donor/acceptor interface area, and improved phase separation. However, DIO adversely affected the overall device performance in PTB7-Th: IEICO-4F and PTB7-Th: ITIC BHJ-OSCs. Furthermore, devices processed with DIO were less photostable and exhibited faster degradation due to the photoacid effect of the DIO additive.
Charge carrier dynamics in PffBT4T-2OD: PCBM organic solar cells
No full textWe investigate the charge carrier dynamics of inverted organic solar cells (OSCs) based on PffBT4T-2OD: PCBM and PTB7: PCBM - the two leading systems among the OSCs based on polymer-fullerene bulk-heterojunction - to elucidate the origin of their performance difference. Transient absorption spectroscopy (TAS) and photo-electrochemical impedance spectroscopy (photo-EIS) were employed to unravel the photo-physics that govern the cell operation of these two highly efficient bulk heterojunction OSCs. While photo-EIS indicates that the two systems under study exhibit similar behavior in terms of recombination, TAS results reveal that PffBT4T-2OD: PCBM systems not only have higher charge generation rate but also more efficient charge transfer than PTB7: PCBM systems, leading to the power conversion efficiency of PffBT4T-2OD: PCBM-based OSCs (9.16%) that is higher than that of PTB7: PCBM-based OSCs (6.44%).
Role of Electronic States and Their Coupling on Radiative Losses of Open-Circuit Voltage in Organic Photovoltaics
No full textVoltage losses (Delta V-OC) are a crucial limitation for the performance of excitonic organic solar cells (OSCs) and can be estimated by two approaches-the radiative limit and the Marcus charge-transfer (MCT) model. In this work, we show that combining the radiative limit and MCT models for voltage loss calculations provides useful insights into the physics of emerging efficient OSCs. We studied nine different donor-acceptor systems, wherein the power conversion efficiency ranges from 4.4 to 14.1% and Delta V-OC varies from 0.55 to 0.95 V. For these state-of-the-art devices, we calculated the Delta V-OC using the radiative limit and the MCT model. Furthermore, we combined both models to derive new insights on the origin of radiative voltage losses (Delta V-rad) in OSCs. We quantified the contribution in Delta V-rad due to the bulk intramolecular (S-1) disorder and interfacial intermolecular (CT) disorder by revisiting the spectral regions of interest for OSCs. Our findings are in agreement with the expected relationship of VOC with Urbach energy (E-U), which suggests that the low E-U is beneficial for reduced losses. However, unprecedentedly, we also identify a universal, almost linear relationship between the interfacial disorder (lambda) and Delta V-rad. We believe that these results can be exploited by the organic photovoltaic (OPV) community for the design of new molecules and a combination of donor-acceptors to further improve OSCs.
Combined effect of ZnO nanoripples and solvent additive on the nanomorphology and performance of PTB7-Th: PC71BM organic solar cells
No full textIn bulk heterojunction organic solar cells (OSCs), nanomorphology of the photoactive layer plays a crucial role in determining photocurrent and fill factor (FF) of OSCs, and therefore it is essential to control the nanomorphology of the photoactive layer to fabricate devices with high power conversion efficiency (PCE). We demonstrate the combined effects of a ZnO nanorippled electron transport layer (ETL) and solvent additive (1,8-diiodooctane (DIO)) on the nanomorphology and performance of a model OSC in an inverted geometry. The photoactive layer in the model OSC is composed of Poly [4,8-bis (5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3- fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl] (PTB7-Th):phenyl-C71-butyric acid methyl ester (PC71BM) blend. It is observed that the use of ZnO nanoripples as an ETL and DIO as a solvent additive facilitates the formation of near ideal nanomorphology of bi-continuous interpenetrating network of donor and acceptor. This is confirmed by morphological studies using atomic force microscopy, scanning electron microscopy and transmission electron microscopy. Photo-electrochemical impedance spectroscopy measurements confirm that obtained nanomorphology of bicontinuous interpenetrating network is contributing to the improved device performance. The device with 3 vol% DIO, with underneath ZnO nanoripples exhibited improved current density (J(sc)), FF, open circuit voltage (V-oc) and PCE of 15.57 mA cm(-2), 64.50%, 0.81V and 8.20%, respectively.
Evincement of Custom Conflicts in Interstates Nuptials Chetan Bhagat’s 2 States
Get PDFIn modern age custom conflicts is the cause of various hazardous problems taking place in contemporary society. The purpose of the present research paper is to portrait the evincement of custom conflicts in Inter states nuptials through Chetan Bhagat’s 2 States or the Story of My Marriage. India is a secular country where people following different custom reside. These distinct cultures and customs prevailing in India somewhere create differences in opinion. Bhagat is known youth’s icon for dealing modern issues in his writing, and as a famous screen writer of contemporary age for film adaptations. He has presented a realistic portraiture of custom conflict between two contrary states Delhi and Tamil. In India inter religion marriage are not accepted, if there is the matter of interstate nuptials love birds have to face great obstacles to win their parents and relatives consent. Bhagat has given an autobiographical touch to this novel. He has portrait a vibrant view of custom conflict and diversities
Malignant hyperthermia in India: Time for awakening, useful facts on Dantrolene
No full textAbstractA 33year old lady with no obvious reason to suspect susceptibility to malignant hyperpyrexia (MH) succumbed to this unexpected complication in spite of attempts to save her life with aggressive supportive measures. We are reporting this case of possible malignant hyperthermia probably the seventh reported case in India and second from Kerala in the last decade (Saxena and Dua, 2007; Punj et al., 2001; Gopalakrishnan et al., 2010; Jain, 2010; Ramakant and Singh, 2012; Sharma et al., 2012). This was the first ever case of MH in our institution in 25years This emphasises the need to ensure availability of Dantrolene and MH kits, diagnostic centres with appropriate lab controls and above all high index of suspicion and heightened awareness among the anaesthesiologists of this potential albeit rare risk of MH in Indian population
Obstructive Sleep Apnea Syndrome: An Under-recognized Clinical Entity with Significant Systemic Morbidities
Get PDFObstructive sleep apnea syndrome (OSAS) is a highly prevalent yet under recognized sleep disorder, characterized by repeated disruptions of breathing during sleep. Not just merely a local phenomenon of upper respiratory tract obstruction, this has many consequences that includes intermittent hypoxia, intermittent hypercapnia, reoxygenation, intra thoracic pressure changes, sympathetic activation, micro-awakenings and sleep fragmentation leading to metabolic dysregulation, endothelial dysfunction, systemic inflammation, oxidative stress, hypercoagulation, and neurohumoral changes that causes excessive daytime sleepiness, neurocognitive deterioration, endocrine, metabolic and other systemic effects including poor quality of life. There are increasing evidences to suggest that OSAS is a systemic inflammatory disease. Epidemiological studies have identified OSAS as an independent risk factor in cardiovascular diseases, metabolic syndrome and bronchial asthma. Patho-physiological changes in OSAS are causally linked to the hypertension with increase risk for heart failure, stroke and cardiovascular mortality. In addition, OSAS is associated with several other disorders and comorbidities that may affect almost every organ systems of our body. Despite having many complex systemic consequences, OSAS and its secondary effects are mostly controllable by continuous positive air pressure (CPAP). This disorder largely remains an underestimated clinical entity due to unawareness by both the patient and physician alike. There is need for awareness regarding this entity among all specialties of medicine and surgery as the so called undetected/occult disease if remain untreated may lead to significant systemic morbidities and at times mortality
Multi class boosted random ferns for adapting a generic object detector to a specific video
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