Organic photovoltaic (OPV) devices have the potential to be superior to other PV technologies in space applications because they can play out two of their main advantages, namely their high flexibility and low weight, maximizing the specific power which is the central figure of merit. With ultrathin active layers of submicron thickness, the heaviest part in OPV technology is the substrate. In outer space, mechanical loading is minimal (no gravitation, wind gusts, or snow loads), so that a further decisive reduction of weight could be achieved by building solar cells without substrates, relying only on the mechanical support of the thin barrier layers that are used for encapsulation.  However, this poses challenges on the reliable multilayer deposition process, as well as on the resilience against folding/unfolding during transport, which must be solved in a cost-effective way that is amenable to mass production.

In this work, we present fully solution-processed (which includes both electrodes) semitransparent organic solar cells (OSCs) without substrates, with performance comparable with conventional indium tin oxide-based devices. Direct cell fabrication onto barrier films leads to the elimination of the additional polyethylene terephthalate substrate and one of the two adhesive layers in the final stack of an encapsulated OPV device by replacing the industrial state-of-the-art sandwich encapsulation with a top-only encapsulation process. This yields significantly thinner and lighter ‘product-relevant’ PV devices. In addition to the increase of the specific power to 0.38 W g−1, which is more than four times higher than sandwich-encapsulated devices, these novel OSCs exhibit better flexibility and survive 5000 bending cycles with 4.5 mm bending radius. Moreover, the devices show comparable stability as conventionally encapsulated devices under constant illumination (1 sun) in ambient air for 1000 h. Finally, degradation under damp heat conditions (65 ◦C, 85% rh) was investigated and found to be determined by a combination of different factors, namely (UV) light soaking, intrinsic barrier properties, and potential damaging of the barriers during (laser) processing. [1]

In the outlook, we discuss how the barrier layers, and the photoactive layer can be stabilized against hard radiation using high throughput experimentation driven by physics-informed artificial intelligence.