Solution-Processed LiF for Tailoring the Work Function in Electrode Bilayers

RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required according to the journal that you are submitting your paper to) Although ambient processing is the key to low-cost organic solar cell production, high-vacuum thermal evaporation of LiF is often a limiting step, motivating the exploration of solution processing of LiF as an alternative electrode interlayer. Sub-monolayer films are realized with the assistance of polymeric micelle reactors that enable LiF particle deposition with controlled nanoscale surface coverage. Scanning Kelvin probe reveals a work function 2 tunable with nanoparticle coverage, with higher values than that of bare tin-doped indium oxide. One of the primary advantages of organic electronics, such as solar cells, is the potential for low-cost mass production of large-area devices. 1-5 While fully vacuum deposited OLEDs have already been introduced into the marketplace, solution-based polymer devices have not been able to effectively take advantage of ambient processing, due to the need for costly and time-consuming vacuum deposition of inorganic electrodes. 1-4 As the current state-of-the-art organic solar cells are based on solution-processed polymer blends, 6 introducing non-vacuum techniques for electrode fabrication remains an essential step in realizing fully ambient manufacturing of devices. Recently, an inverted device structure deposited entirely from solution was realized by Krebs and co-workers for roll-to-roll manufacturing. 1-4 This achievement demonstrates the feasibility of complete ambient processing, consequently inspiring the development of more suitable materials systems. Though a wide variety of interlayers have been attempted in organic devices, LiF has seen widespread use at both high work function 7-9 and low work function 10-12 electrodes, due to the dramatic enhancement of electrode properties. Despite the fact that the exact mechanism is still controversial, LiF is known to mainly affect the electrode surface work function (Φ), which plays a central role in determining the efficiency and performance of a device. While other solution processed interlayers have been realized, including most recently CsF 17 and ZnO nanoparticles, 1-4 the incorporation of LiF to date still necessitates high-vacuum techniques, due to the poor solubility of LiF. However, the versatility of LiF for use at both 3 electrodes makes a compelling case for the development of a solution-processed route for LiF, for the eventual use with an appropriate solution processed electrode at the top-side contact. Electrode work function () plays a major role in the performance of devices, as adjustment of Φ results in changes of the …