All sub‐nanosecond laser monolithic interconnection of OPV modules

Abstract

Although green femtosecond lasers provide outstanding quality and wide processing windows for monolithic interconnection of the individual cells in organic photovoltaic (OPV) modules, they are hardly used in commercial applications, due to cost reasons.In this work, a process has been developed that allows the monolithic interconnection in OPV modules with an infrared sub-nanosecond laser exclusively, without compromising the performance of the modules. While the photoactive layer is removed easily by green femtosecond pulses without damaging the bottom electrode, this is not possible for infrared nanosecond pulses, due to their much larger optical penetration length, which significantly exceeds the thickness of the active layer and is well absorbed by the indium tin oxide (ITO) layer. This leads to damage of the ITO bottom electrode, which in turn compromises the functionality of the module.By systematically varying single-pulse laser fluence and spatial pulse overlap, the laser parameters are optimized in such a way that the contact area between the residues of the metal oxide bottom electrode and the silver nanowire top electrode is maximized so that the electrical resistances of the contacts are sufficiently small not to affect device performance. This is demonstrated by presenting large-area OPV modules based on the well-characterized reference system P3HT:PCBM that show efficiencies of up to 2.4%. This achievement opens up the way towards reliable roll-to-roll (R2R) laser patterning processes with sub-nanosecond lasers and thus represents a breakthrough with respect to cost-effective R2R manufacturing of OPV modules, due to grossly reduced investment and maintenance costs for laser sources. KEYWORDS flexible organic photovoltaic module, laser patterning, sub-nanosecond pulses 1 | INTRODUCTION Besides flexibility, lightweight, semitransparency, and customized color and shape, the attractiveness of polymer-based organic photovoltaics (OPVs) is based on the possibility of cost-effective deposition of the modules from the liquid phase on large areas by roll-to-roll (R2R) processes. 1 In order to avoid resistive losses and to provide useful voltages, the modules are divided into several cells, which are serially interconnected. The area needed for interconnection is inactive for PV energy generation and is therefore named dead area. The geometrical fill factor (GFF) is defined by the ratio of the PV active area and the total module area and enters directly the calculation of the module efficiency. Traditionally, the interconnection of individual cells is achieved by printing a bottom electrode, the photoactive layer,

Organic photovoltaic modules with new world record efficiencies

“…We will also demonstrate that the required quality of laser patterning can be achieved with ns-lasers, rather than requiring fs-lasers, thus reducing the capex for production equipment by an order of magnitude. 14…”

Organic Solar Cells—The Path to Commercial Success

“…This process, which is well established for the monolithic series connection of inorganic thin film technologies, has been used to achieve geometric fill factor of well above 95% and low interconnect losses for OSC modules. [94,95] OSC modules will be exposed to relatively harsh environments during operation, requiring protection in particular against water vapor, oxygen, UV light, mechanical stresses, and combinations thereof, which can all lead to loss in performance (see also 2.2). [44,47] The exact requirements for the encapsulation vary depending on the used materials and stack design as well as the products (wearable electronics, building integrated photovoltaics, etc.).…”

Progress in Materials, Solution Processes, and Long‐Term Stability for Large‐Area Organic Photovoltaics

“…[17,101,110,171] To prevent the resistive losses at the interconnections and minimize a dead area, precise design and patterning techniques such as laser ablation are required. [172,173] Studies on crystalline silicon solar modules already evidenced the degradation of interconnections which had experienced field temperature cycling. Thermal cycling induces thermo-mechanical stress and cracks of the solder interconnection caused by mismatch of thermal expansion coefficient between the module material and the ribbon wire solder.…”