Ionic-liquid doping enables high transconductance, fast response time, and high ion sensitivity in organic electrochemical transistors

Organic electrochemical transistors (OECTs) are highly attractive for applications ranging from circuit elements and neuromorphic devices to transducers for biological sensing, and the archetypal channel material is poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS. The operation of OECTs involves the doping and dedoping of a conjugated polymer due to ion intercalation under the application of a gate voltage. However, the challenge is the trade-off in morphology for mixed conduction since good electronic charge transport requires a high degree of ordering among PEDOT chains, while efficient ion uptake and volumetric doping necessitates open and loose packing of the polymer chains. Ionic-liquid-doped PEDOT:PSS that overcomes this limitation is demonstrated. Ionic-liquid-doped OECTs show high transconductance, fast transient response, and high device stability over 3600 switching cycles. The OECTs are further capable of having good ion sensitivity and robust toward physical deformation. These findings pave the way for higher performance bioelectronics and flexible/wearable electronics.ASTAR (Agency for Sci., Tech. and Research, S’pore)Accepted versio

Enhancing moisture tolerance in efficient hybrid 3D/2D perovskite photovoltaics

Surface imperfections in perovskite films upon crystallization may trigger trap-assisted non-radiative recombination which is a dominant recombination mechanism that potentially restricts the performance of solar devices. In this work, 2D alkylammonium halide perovskites are formed on the 3D perovskite structure to passivate interfacial defects and vacancies and enhance moisture tolerance. The hybrid 3D/2D perovskite films possess longer photoluminescence lifetimes, as well as lower trap state densities, indicating the passivation of cationic and halide vacancies on the surface or grain boundaries, thereby reducing the non-radiative recombination pathways. More importantly, the hybrid 3D/2D perovskite exhibits higher ambient stability than a pure 3D perovskite where the hydrophobic nature of the long aliphatic carbon chains in the 2D perovskite provide an additional moisture repelling effect to the entire perovskite film. With this approach, the power conversion efficiency of perovskite solar cells was improved from 14.17% to 15.74% along with improved device stability. The hybrid 3D/2D perovskite solar cell retained 86% of its initial power conversion efficiency whereas the control device lost almost 40% of its overall efficiency. Thus, the hybrid 3D/2D perovskite structure is an alternative solution for modulating defects and trap-state densities in high efficiency perovskite solar cells with simultaneously enhanced moisture stability.NRF (Natl Research Foundation, S’pore)MOE (Min. of Education, S’pore)Accepted versio