Improved Efficiency and Stability of Organic Solar Cells by Interface Modification Using Atomic Layer Deposition of Ultrathin Aluminum Oxide

Abstract

The interfacial contacts between the electron transporting layers (ETLs) and the photoactive layers are crucial to device performance and stability for OSCs with inverted architecture. Herein, atomic layer deposition (ALD) fabricated ultrathin Al2O3 layers are applied to modify the ETLs/active blends (PM6:BTP‐BO‐4F) interfaces of OSCs, thus improving device performance. The ALD‐Al2O3 thin layers on ZnO significantly improved its surface morphology, which led to the decreased work function of ZnO and reduced recombination losses in devices. The simultaneous increase in open‐circuit voltage (), short‐circuit current density () and fill factor (FF) were achieved for the OSCs incorporated with ALD‐Al2O3 interlayers of a certain thickness, which produced a maximum PCE of 16.61%. Moreover, the ALD‐Al2O3 interlayers had significantly enhanced device stability by suppressing degradation of the photoactive layers induced by the photocatalytic activity of ZnO and passivating surface defects of ZnO that may play the role of active sites for the adsorption of oxygen and moisture.

Tuning Surface Defect States in Sputtered Titanium Oxide Electron Transport Layers for Enhanced Stability of Organic Photovoltaics

“…These formed hydroxyl radicals chemically react with and decompose the organic NFA molecules, as demonstrated by the well-known ITIC NFA system . Several routes have been shown to mitigate this effect, for example via C 60 self-assembled monolayers or via different surface treatments that passivate the surface defects leading to the hydroxyl radical-mediated degradation mechanisms. − While some of these methods have presented good stability, they appear as challenging to scale up due to a lack of compatibility with roll-to-roll-based techniques, and thus alternative solutions must be explored. Another approach to limiting the photocatalytic degradation of NFA molecules by metal oxide ETLs is replacing TiO x and ZnO ETLs with other metal oxides that do not have a strong photocatalytic activity, e.g., SnO 2 …”

Simultaneous improvement in efficiency and photostability of organic solar cells by modifying the ZnO electron-transport layer with curcumin

“…20,21 Nevertheless, ZnO has intrinsic limitation that it can be trapped in the ''light-soaking'' problem and thereby produce reactive free radicals upon exposure to ultraviolet light, resulting in the decomposition of photovoltaic materials. [22][23][24][25][26] Meanwhile, the unbalanced stoichiometric proportion of zinc and oxygen atoms during the formation of the ZnO film inevitably generates oxygen vacancies (VO + ) and zinc interstitial (Zni + ) defects. 27,28 These defects not only act as recombination centres to capture photogenerated carriers, but also absorb environmental oxygen and water, which seriously impair the electrical conductivity and lifetime of i-OSCs.…”

Uncovering the Electronic State Interplay at Metal Oxide Electron Transport Layer/Nonfullerene Acceptor Interfaces in Stable Organic Photovoltaic Devices

“…These reactions lead to the formation of hydroxyl radicals, which can cause decomposition of the organic molecules . While there has been several strategies to passivate such surface defects or suppress the photocatalytic activity of NFAs on ZnO to improve photostability, − a more elegant and also practical approach is to overcome this degradation by developing metal oxide ETLs that possess lower photocatalytic activity, such as SnO 2 . In this context, we have recently shown that tuning the surface oxygen content in sputter-deposited TiO x ETLs enhances the long-term stability of PBDB-T:ITIC-based OPV devices significantly, when compared to conventional solution-processed metal oxide ETLs, due to reduced photocatalytic decomposition of the NFA molecule ITIC at the metal oxide ETL .…”