Demonstrators for autonomous automotive and signage applications by bonding flexible solar cells, batteries and LED elements on large area polycarbonate backplanes

Autonomous systems are pursued in automotive and signage applications due to easy installation and achieved energy savings. In addition, reduction of cabling decreases system weight, which is especially pursued in automotive applications due to the decreased fuel consumption. Naturally, autonomous systems require some kind of energy harvesting and energy storing systems. In order to achieve required autonomy operation time of over 15 hours, four flexible Li-Ion batteries of 1200 mAh total capacity in automotive demonstrator and four flexible Li-Ion batteries of 3200 mAh total capacity in signage demonstrator were required. The dimensions of batteries were 295 mm × 29 mm and 295 mm × 119 mm. The energy harvesting for autonomous operation was based on flexible commercially available amorphous silicon solar cells, types MP3-25 and MPT6-150 manufactured by Power Film. The dimensions of the solar cells were 114 mm × 29 mm and 114 mm × 150 mm. The pursued autonomy time of demonstrators resulted to a large surface area requirement for the backplane substrates. The dimensions of the assembled automotive demonstrator were 2400 mm × 35 mm × 0.95 mm and the dimensions of the assembled signage demonstrator were 2550 mm × 144 mm × 0.95 mm. The large size of both the components and the substrates produced challenges for assembly and bonding processes. As the bonding method hot bar bonding or oven curing were used, the experimental procedure being compatible with the guidelines of the material suppliers. Daisy chain test structures were used to study the interconnections between the foils. Thermal humidity testing at 85°C/85%RH and thermal cycling between −40….+85°C were used as the environmental tests for the test structures processed before final selection of the bonding materials and processes for demonstrators manufacturing. Both manufactured demonstrators were operational after assembly and bonding processes. The energy produced by the solar cells was guided to the Li-Ion batteries by a specific charge regulator. Batteries were able to supply power to the automotive and signage LED elements so that the systems autonomous operation was successfully demonstrated.