Ritu Gupta

Bio: Ritu Gupta is an academic researcher from Indian Institute of Technology, Jodhpur. The author has contributed to research in topics: Coating & Grating. The author has an hindex of 20, co-authored 60 publications receiving 1409 citations. Previous affiliations of Ritu Gupta include Purdue University & Jawaharlal Nehru Centre for Advanced Scientific Research.

Solution processed large area fabrication of Ag patterns as electrodes for flexible heaters, electrochromics and organic solar cells

Abstract: A simple method for producing patterned Ag electrodes on transparent and flexible substrates is reported. The process makes use of a laser printed toner as a sacrificial template for an organic precursor, which upon thermolysis and toner lift off produced highly conducting Ag electrodes. Thus, the process takes only a few minutes without any expensive instrumentation. The electrodes exhibited excellent adhesion and mechanical properties, important for flexible device applications. Using Ag patterned electrodes, heaters operating at low voltages, pixelated electrochromic displays as well as organic solar cells have been demonstrated. The method is extendable to produce defect-free patterns over large areas as demonstrated by roll coating.

Towards low cost materials and methods for transparent electrodes

Abstract: A transparent electrode is a key component of any optoelectronic or transparent device. With increasing number of large area applications, there is growing demand to replace the conventional oxide based transparent conducting films with nanomaterials, primarily to reduce the cost. This review deals with a range of materials and processes forming new generation transparent electrodes, while giving some insight into the cost.

Large area defrosting windows based on electrothermal heating of highly conducting and transmitting Ag wire mesh

Abstract: Highly interconnected crackles were obtained by spreading commercially available low cost crackle wall paint based precursor by the drop coating technique. An interconnected Ag mesh was fabricated by depositing metal over the crackle network followed by the removal of the template. The metal network is well conducting (1 Ω □−1) with transmittance of ∼77% over the fabricated area, 18 × 15 cm2. By joule heating using few volts, uniform temperatures up to 170 °C were achieved on the electrode area and a high thermal resistance of 255.2 °C cm2 W−1 was obtained. The electrode was tested for defrosting application by exposing it to liquid nitrogen (LN2) vapors at ∼−60 °C while applying 8.5 V for 2 min, when the frost disappeared making the display board below, visible. The transparent heater could successfully withstand an ultrasonication test, as well as many defrosting cycles.

A cracked polymer templated metal network as a transparent conducting electrode for ITO-free organic solar cells.

Abstract: We report a highly transparent, low resistance Ag metal network templated by a cracked polymer thin film and its incorporation in an organic solar cell. The performance of this scalable metallic network is comparable to that of conventional ITO electrodes. This is a general approach to replace ITO in diverse thin film devices.

Outdoor operational stability of indium-free flexible polymer solar modules over 1 year studied in India, Holland and Denmark

Abstract: We present an outdoor interlaboratory stability study of fully printed and coated indium-tin-oxide (ITO)-free polymer solar cell modules in JNCASR Bangalore (India), ECN (Holland), and DTU (Denmark) carried over more than 1 year. The modules comprising a fully printed and coated stack (Ag grid/PEDOT:PSS/ZnO/P3HT:PCBM/PEDOT:PSS/Ag grid) were prepared in two successive generations and evaluated for outdoor operational stability according to the test protocols laid out by the International Summit on OPV stability (ISOS-3). The modules (70–100 cm 2 active area) were encapsulated between two sheets of low-cost plastic barrier material with the use of a UV curing adhesive. The impact of differences in the climatic conditions on the performance of the modules is highlighted and the performance of the modules under storage conditions in parallel with the outdoor study is investigated. While all Gen-I modules failed, the best devices of Gen-II module in which simple improvement in the encapsulation scheme (Gen-II modules) was carried out maintained 95% of the initial performance after 1 year of outdoor testing. We provide detailed insight into the failure mode and offer a discussion on the need for improvement in flexible encapsulation. Finally, recommendations on future encapsulation schemes are also presented.

Reducing the efficiency–stability–cost gap of organic photovoltaics with highly efficient and stable small molecule acceptor ternary solar cells

Abstract: Technological deployment of organic photovoltaic modules requires improvements in device light-conversion efficiency and stability while keeping material costs low. Here we demonstrate highly efficient and stable solar cells using a ternary approach, wherein two non-fullerene acceptors are combined with both a scalable and affordable donor polymer, poly(3-hexylthiophene) (P3HT), and a high-efficiency, low-bandgap polymer in a single-layer bulk-heterojunction device. The addition of a strongly absorbing small molecule acceptor into a P3HT-based non-fullerene blend increases the device efficiency up to 7.7 ± 0.1% without any solvent additives. The improvement is assigned to changes in microstructure that reduce charge recombination and increase the photovoltage, and to improved light harvesting across the visible region. The stability of P3HT-based devices in ambient conditions is also significantly improved relative to polymer:fullerene devices. Combined with a low-bandgap donor polymer (PBDTTT-EFT, also known as PCE10), the two mixed acceptors also lead to solar cells with 11.0 ± 0.4% efficiency and a high open-circuit voltage of 1.03 ± 0.01 V. Ternary organic blends using two non-fullerene acceptors are shown to improve the efficiency and stability of low-cost solar cells based on P3HT and of high-performance photovoltaic devices based on low-bandgap donor polymers.

Stability of organic solar cells: challenges and strategies

Abstract: Organic solar cells (OSCs) present some advantages, such as simple preparation, light weight, low cost and large-area flexible fabrication, and have attracted much attention in recent years. Although the power conversion efficiencies have exceeded 10%, the inferior device stability still remains a great challenge. In this review, we summarize the factors limiting the stability of OSCs, such as metastable morphology, diffusion of electrodes and buffer layers, oxygen and water, irradiation, heating and mechanical stress, and survey recent progress in strategies to increase the stability of OSCs, such as material design, device engineering of active layers, employing inverted geometry, optimizing buffer layers, using stable electrodes and encapsulation. Some research areas of device stability that may deserve further attention are also discussed to help readers understand the challenges and opportunities in achieving high efficiency and high stability of OSCs towards future industrial manufacture.

Consensus statement for stability assessment and reporting for perovskite photovoltaics based on ISOS procedures

Abstract: Improving the long-term stability of perovskite solar cells is critical to the deployment of this technology. Despite the great emphasis laid on stability-related investigations, publications lack consistency in experimental procedures and parameters reported. It is therefore challenging to reproduce and compare results and thereby develop a deep understanding of degradation mechanisms. Here, we report a consensus between researchers in the field on procedures for testing perovskite solar cell stability, which are based on the International Summit on Organic Photovoltaic Stability (ISOS) protocols. We propose additional procedures to account for properties specific to PSCs such as ion redistribution under electric fields, reversible degradation and to distinguish ambient-induced degradation from other stress factors. These protocols are not intended as a replacement of the existing qualification standards, but rather they aim to unify the stability assessment and to understand failure modes. Finally, we identify key procedural information which we suggest reporting in publications to improve reproducibility and enable large data set analysis. Reliability of stability data for perovskite solar cells is undermined by a lack of consistency in the test conditions and reporting. This Consensus Statement outlines practices for testing and reporting stability tailoring ISOS protocols for perovskite devices.

Advances in colloidal assembly: the design of structure and hierarchy in two and three dimensions.

Abstract: This Review highlights the large number of methods to exploit colloidal assembly of comparably simple particles with nano- to micrometer dimensions in order to access complex structural hierarchies from nanoscopic over microscopic to macroscopic dimensions