Simulative Investigations of the Mechanical Reliability of the Flexible Optoelectronic Packaging Using Optodic Bonding
With the constant innovation and development of the advanced materials and technologies in the field of optoelectronics, a variety of applications adopting the benefits of optoelectronics is increasingly penetrating into our daily routines. The way of packaging has a huge impact on the performance of optoelectronics in mechanical, electrical as well as optical properties. Particularly, flexible packaging is becoming a trend thanks to its compatibility to any irregular surfaces in diverse applications. By employing transparent polymer foils, such as polymethyl methacrylate (PMMA) and polyethylene terephthalate (PET), as carrier substrates for optoelectronic packaging, a greater mechanical flexibility can be achieved. Their transparency expands the range of application, for instance in optical sensing areas. In addition, they are mostly cost-effective, which enables an economical roll-to-roll manufacturing process. However, the challenge of using them is their low glass transition temperatures. In previous works, a novel optodic bonding process employing UV curable adhesives for processing these thermally sensitive polymer foils was introduced and verified as a promising technology for flexible optoelectronic packaging. In this work, we conduct further investigations of its mechanical reliability with the focus on the aspect of flexibility. FEM-based simulations for emulating various mechanical loadings including shear, bending and tensile stresses are implemented. We perform analyses of the influencing factors, particularly their degree of efficiency on the mechanical stability, e.g. the material properties of the optoelectronic components, the employed polymers as well as the bonding adhesives. These comprehensive investigations establish a constructive guideline for choosing materials for flexible optoelectronic packaging. In addition to this, we attain a convincing statement for the reliable feasibility of the optodic bonded packages with respect to a sufficient mechanical flexibility and stability.
Advanced flexible electronics: challenges and opportunities
Thin, lightweight and flexible electronics are being regarded as an important evolutionary step in the development of novel technological products. Interestingly, this trend has emerged in a wide range of industries; from microelectronics to photovoltaics and even solid state lighting. Historically, most attempts to enable flexibility have focused on the introduction of new material systems that, so far, severely compromise the performance compared to state-of-the-art products. The few approaches that do attempt to render contemporary high-performance materials flexible rely on layer transfer techniques that are complicated, expensive and material-specific. In this paper, we review a method of removing surface layers from brittle substrates called Controlled Spalling Technology that allows one to simple peel material or device layers from their host substrate after they have been fabricated. This allows one to fabricate high-performance electronic products in a manner of their choosing, and make them flexible afterwards. This technique is simple, inexpensive and largely independent of substrate material or size. We demonstrate the power and generality of Controlled Spalling by application to a number of disparate applications including high-performance integrated circuits, high-efficiency photovoltaics and GaN-based solid state lighting.
Ultralight High‐Efficiency Flexible InGaP/(In)GaAs Tandem Solar Cells on Plastic
Flexible solar cells are envisioned to open up a myriad of possibilities for enabling new applications in consumer electronics and space satellites. [ 1–3 ] Organic and amorphous semiconductors hold a great promise for realizing bendable and light-weight solar cells, largely due to their fairly strong light absorption properties, process temperature compatibility with fl exible substrates and potentially inexpensive processing cost. [ 4–6 ] However, the poor minority carrier lifetime in these materials, inherent to their highly disordered and defective crystalline structure, inhibit their use for making high effi ciency and reliable solar cells. This limitation becomes more pronounced in applications with stringent specifi cations in terms of the total area and weight of the photovoltaic (PV) module. Conversely, the exquisite optical and electrical properties of III–V semiconductors permit the fabrication of extremely high-effi ciency solar cells exploiting thin III–V layers. [ 7–9 ] For example, multijunction III–V solar cells have currently reached ≥ 36% conversion effi ciency at one sun intensity, for which the total thickness of the solar cell structure is ≤ 10 μ m. [ 10 ] However, III–V solar cells are conventionally grown on mechanically rigid gallium arsenide (GaAs) and germanium (Ge) substrates that serve as an epitaxial template. Therefore, the release of thin III–V layers from the growth substrate is essential for rendering the solar cell structure fl exible. Furthermore, there has been a growing interest in exploiting inverted metamorphic structures to attain higher conversion effi ciency, in which the removal of the solar cell structure from the growth substrate is necessary for the proper function of the device. [ 7 , 10 ] It is also important to consider that the use of a viable layer transfer scheme will ideally lead to substantial reduction in material cost by enabling (i) substrate reuse and (ii) thinner solar cell structures with potentially higher conversion effi ciency utilizing back refl ectors. [ 11 , 12 ]