A Systematic Investigation of Permeation Barriers for Flexible Dye‐Sensitized Solar Cells

Abstract

Dye solar cells (DSCs), in their flexible form, are prone to ageing due to ingress of gas as a result of the intrinsic permeability of polymer substrates. Thus, it is important to develop proper encapsulation strategies to limit degradation. Literature on flexible DSCs lacks comparative tests with different permeation barriers, including flexible ultrahigh barriers (UHB). We designed such tests and applied UHBs to flexible DSCs for the first time. We demonstrate that UHBs double the lifetime of cells with respect to those with none or less‐effective barriers. Degradation is due to a combination of electrolyte bleaching, dye detachment, and indium tin oxide (ITO) degradation. The reduced, though still noticeable, performance loss for UHB‐ and glass‐equipped cells can be mainly ascribed to lateral permeation of gas/water, suggesting that efficient solutions for edge encapsulation must be developed to extend lifetimes further.

Quantifying Performance of Permeation Barrier—Encapsulation Systems for Flexible and Glass‐Based Electronics and Their Application to Perovskite Solar Cells

“…After the much longer period of 4344 h the average PCE values were measured to be 60% and 30% of the initial values for glass and UHPBF‐S indicating the effect of water and oxygen ingress. For glass ingress occurs laterally mainly through the resin and at its interfaces . Although the averages were lower, the large error bar on the UHPBF‐S for the last data point indicates that in the best case PCE values approached those for glass even after such a long test, but the gap and reproducibility over many samples of the flexible barriers can be improved by minimizing pinholes and defects during fabrication, handling, application and gluing procedures.…”

“…To avoid moisture and oxygen ingress and further degradation, devices must be encapsulated with permeation barriers ensuring a water vapor transmission rate (WVTR) range of 10 −3 to 10 −6 g m −2 d −1 and an oxygen transmission rate (OTR) between 10 −2 and 10 −5 cm 3 m −2 d −1 . Encapsulation of rigid devices is relatively straightforward, where glass or metal sheets are applied with appropriate sealants.…”

“…For flexible devices, especially where transparency of the barrier is required (e.g., for displays or photovoltaic modules), the solutions are more complex since plastics are highly permeable to gasses. Currently, the encapsulation methods consisted in direct deposition of a protective thin films (i.e., Al 2 O 3 or Parylene C), or the application of permeation barrier film using a sealant or adhesive (e.g., epoxy, ultraviolet UV‐curable or silicone‐based resins, hotmelts, thermoplastic films, pressure sensitive or bifacial adhesives) on the devices. Protective film deposition directly on the device typically, although effective, requires the laboratory or industry to possess a high‐cost vacuum‐based equipment/process (e.g., atomic layer deposition—ALD) as well as detailed understanding of the interaction between the deposition process, the barrier layer material, and the device structure.…”

“…Similarly, Hermenau et al showed that the quantity of water increase to 15.5 g m −2 when OSC were tested at 45 °C and 5.5% RH. De Rossi et al first carried out a systematic investigation of flexible barriers on dye sensitized solar cells estimating that gas ingress by lateral permeation was the main culprit for permeation on small‐ and medium‐sized cells. Notably, there are no reports unravelling the direct correlation between the permeation rates (i.e WVTR values) and lifetime performance (i.e., PCE degradation) of encapsulated perovskite solar cells.…”

Recent progress in flexible dye solar cells

“…For the sealing of organic photovoltaic devices, the commonly targeted scale of WVPR is 10 −6 /g 2 day 1 (Seethamraju et al, 2014(Seethamraju et al, , 2016. For instance, ITO-PET commonly applied in flexible DSCs has been estimated to permeate 10 −1 /g 2 day 1 (De Rossi et al, 2016). However, an estimate for an acceptable WVPR for DSCs has not been made.…”