{"id":1270,"date":"2013-07-25T18:27:15","date_gmt":"2013-07-25T18:27:15","guid":{"rendered":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/?p=1270"},"modified":"2013-07-25T18:30:00","modified_gmt":"2013-07-25T18:30:00","slug":"nano-thin-encapsulation-of-photovoltaics-via-atomic-layer-deposition","status":"publish","type":"post","link":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/nano-thin-encapsulation-of-photovoltaics-via-atomic-layer-deposition\/","title":{"rendered":"Nano-thin Encapsulation of Photovoltaics via Atomic Layer Deposition"},"content":{"rendered":"

Device lifetime is a key figure of merit for solar cells and impacts the levelized energy cost ( $\/(kW*hr) ) of a photovoltaic module[1<\/a>]<\/sup>.\u00a0 Its importance necessitates the encapsulation of solar cells; however, the prevalent commercial encapsulation (polymer thin film plus glass sheet) is inflexible and heavy, thereby increasing the installation and balance-of-systems costs.\u00a0 In this work we implement a nano-thin metal oxide film deposited by atomic layer deposition (ALD) as an encapsulation layer for organic photovoltaics[2<\/a>]<\/sup>.\u00a0 With ALD we deposit a 27-nm nano-thin film of alternating layers of HfOx and AlOx[3<\/a>]<\/sup> directly on top of the cathode of photovoltaics composed of either polymer bulk heterojunction or molecular planar-mixed heterojunction photoactive layers (Figure 1). The effect of the ALD process on the device performance and furthermore the dependence of lifetime on photoactive materials choice selection and cathode composition are examined.\u00a0 While the absolute lifetime of the devices depends on the composition of the photoactive film as well as the cathode, all devices displayed significant increases in lifetime when encapsulated with ALD nano-thin films versus no encapsulation. Molecular OPVs with Al electrodes and ALD nano-thin encapsulant exhibit less than 10% decay in efficiency over 1200 hours storage in air.\u00a0 As shown in Figure 2, aAddition of ALD nano-thin encapsulant to polymer PVs with Al electrodes increases device lifetime by up to 5,000%.<\/p>\n\n\t\t