Anisotropic Conductive Adhesives for Interdigitated Back Contact (IBC) Silicon Solar Cells

The current manufacturing process for solar panels using interdigitated back contact (IBC) silicon solar cells involves a multi-step metallization and interconnection process in which a substantial amount of silver is used. This work focuses on a new process using conductive adhesives (CA) which would increase efficiency and lower cost through a one-step metallization and interconnection process that combines with encapsulation using little silver and only requiring metal patterning on the back sheet or back glass. It would also not require direct metallization of the silicon, which would result in fewer defects, while increasing voltage and therefore efficiency. Silver-coated Poly(Methyl Methacrylate) Microsphere (AgMS) and indium powder are the primary materials used as the conductive particles in an ethyl vinyl acetate (EVA)/toluene adhesive. The CA is prepared by mixing the components in toluene. The resulting mixture is used to produce 300μm thick CA sheets using a universal applicator, cut into pieces, and pressed between a piece of glass with coplanar Ag electrodes and a silicon wafer at varying temperatures and pressures. This yields ~3 Ωcm2 for both the AgMS and indium fillers. Significantly lower values are required for the target application, and possible new approaches in attaining lower resistivity are discussed

INKJET PRINTING OF NICKEL AND SILVER METAL SOLAR CELL CONTACTS

ABSTRACT With about 125,000 terawatts of solar power striking the earth at any given moment, solar energy may be the only renewable energy resource with enough capacity to meet a major portion of our future energy needs. Thin-fi lm technologies and solution deposition processes seek to reduce manufacturing costs in order to compete with conventional coal-based electricity. Inkjet printing, as a derivative of the direct-write process, offers the potential for low-cost, material-effi cient deposition of the metals for photovoltaic contacts. Advances in contact metallizations are important because they can be employed on existing silicon technology and in future-generation devices. We report on the atmospheric, non-contact deposition of nickel (Ni) and silver (Ag) metal patterns on glass, Si, and ZnO substrates at 180-220°C from metal-organic precursor inks using a Dimatix inkjet printer. Near-bulk conductivity Ag contacts were successfully printed up to 4.5 μm thick and 130 μm wide on the silicon nitride antirefl ective coating of silicon solar cells. Thin, high-resolution Ni adhesion-layer lines were printed on glass and zinc oxide at 80 μm wide and 55 nm thick with a conductivity two orders of magnitude less than the bulk metal. Additionally, the ability to print multi-layered metallizations (Ag on Ni) on transparent conducting oxides was demonstrated and is promising for contacts in copper-indium-diselenide (CIS) solar cells. Future work will focus on further improving resolution, printing full contact devices, and investigating copper inks as a low-cost replacement for Ag contacts

Hydrazine-free solution-deposited CuIn(S,Se)2 solar cells by spray deposition of metal chalcogenides

Solution processing of semiconductors, such as CuInSe2 and its alloys (CIGS), can significantly reduce the manufacturing costs of thin film solar cells. Despite the recent success of solution deposition approaches for CIGS, toxic reagents such as hydrazine are usually involved, which introduce health and safety concerns. Here, we present a simple and safer methodology for the preparation of high-quality CuIn(S, Se)2 absorbers from metal sulfide solutions in a diamine/dithiol mixture. The solutions are sprayed in air, using a chromatography atomizer, followed by a postdeposition selenization step. Two different selenization methods are explored resulting in power conversion efficiencies of up to 8%

Scalable deposition of high-efficiency perovskite solar cells by spray-coating

Spray-deposition is a low-cost, roll-to-roll compatible technique that could potentially replace spin-coating for the deposition of highly efficient perovskite solar cells. Here, perovskite active layers were fabricated in air using an ultrasonic spray system and compared with equivalent spin-coated films. A chlorine-containing perovskite ink with a wide processing window coupled with an antisolvent extraction resulted in perovskite films with relatively rougher surfaces than those spin-coated. A power conversion efficiency (PCE) of 17.3% was achieved with an average of 16.3% from 24 devices. Despite observing differences in film roughness and structure, the performance of sprayed perovskite solar cells was comparable to that of the spin-coated cells processed in an inert atmosphere, showing the versatility of perovskite processing

Developing new functional TCs

Transparent Conductors (TCs) are increasingly critical to the performance and reliability of a number of technologies. Traditionally based primarily on oxides of Ga, In, Zn and Sn the class is rapidly expanding into new materials including both other oxides and more recently composites of metallic or carbon nanowires. Many of these materials offer unique functionality as well as processing and reliability advantages over some of the historic materials. These compounds are all classically non-stoiciometric and often metastable consisting of oxide, non-oxide and composite materials which are being collectively looked at for an increasingly broad set of applications including photovoltaics, solid state lighting, power electronics and a broad class of flexible and wearable electronics. In this talk, we will focus on two main areas; the development of predictive models to be able to identify dopants and the processing regimes where they can be activated as well as the use of nanowire oxide composites to develop a new generation of tunable high performance TC. The complex set of demands for a desired TC include not only classical performance, but also processibility, cost and reliability necessitating a search for new materials. The ability to use materials genomics to identify new dopable TC materials that are experimentally realizable is rapidly increasing. We will discuss recent work on predicting the dopability of Ga2O3 films, which potentially have broad applicability as buffer layers, TCOs, and in power electronics if the doping level can be well controlled. We will discuss the theoretical predictions for the process windows to activate both Sn and Si as dopants and compare this to experimental results and the literature. We will also present resent results on the theoretical prediction and realization of a new p-type TC based on CuZnS, which has demonstrated conductivities of up to 100 S/cm. The latter while not classically an oxide is certainly non-stoichiometric and properties are enhanced in many cases by the use of complex oxide, sulfide and selenide materials. Together these will illustrate the evolving tools both theory and experiment to develop and realize dopants in wide band gap materials. In cases where single materials may not be sufficient, nanowire (metal or carbon based) composites with oxides is increasingly attractive. For example, Ag, and potentially Cu, nanowires embedded in a metal oxide matrix can potentially produce TCs that can be processed at low temperature, have conductivity and transparency comparable to the best TCOs, control interface stability and electronic properties and are suitable to flexible electronics. We will present work on ZnO, InZnO and ZnSnO composites with Ag nanowires where the performance can be as good as high quality InSnO with films Rs\u3c 10 Ohms/sq. We will discuss the dependence on the interrelationship between the nanowire properties and the oxide properties. We will also discus the concept of employing sandwich oxides to separately optimize the top and bottom interfacial properties. This work was supported, in part, by the Center for the Next Generation of Materials by Design, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. This research also supported in part by the Solar Energy Research Institute for India and the U.S. (SERIIUS) funded jointly by the U.S. Department of Energy subcontract DE AC36-08G028308 (Office of Science, Office of Basic Energy Sciences, and Energy Efficiency and Renewable Energy, Solar Energy Technology Program, with support from the Office of International Affairs) and the Government of India subcontract IUSSTF/JCERDC-SERIIUS/2012 dated 22nd Nov. 2012

Importance of interfaces in hybrid perovskite solar cells

Photovoltaic devices based on hybrid organic-inorganic perovskite absorbers have reached outstanding performance over the past few years, surpassing power conversion efficiency of over 22%. In this talk we discuss the role of the interface in optimizing device performance as measured by both power conversion efficiency and stability. We present an examination of different perovskite active layers and interfacial electronic structure of these remarkable materials with functional oxide and organic contact layers. Interface formation of the active layer with different carrier transport materials has direct implications for performance of the resulting devices. We present interface studies, which permit identification of charge transfer mechanisms across the interface with chemical specificity and insight into the requirements for realizing high performance devices. Our findings from surface science approaches are combined with time resolved spectroscopy, structural studies and device level studies to validate impacts on carrier dynamics and demonstrate their technological relevance of interfacial insights