Hybrid 3D/2D perovskites combine the high efficiency of 3D perovskites and the stability of 2D perovskites, and possess longer photoluminescence lifetimes, lower trap-state densities and enhanced moisture tolerance. The hybrid 3D/2D structure is a successful strategy to improve stability without sacrificing conversion efficiency.

The use of organic electrochemical transistors (OECTs) for various applications ranging from neuromorphic devices [1] to transducers for biological sensing, including detection of ions, [2,3] metabolites (such as glucose [4,5] ), DNA, [6] antibodyantigen interaction, [7] and cancer cells [8] has received significant attention in recent years. An OECT consists of a conjugated polymer channel in direct contact with an electrolyte, where the operation involves doping and dedoping of the conjugated polymer by reversible exchange of ions present in an electrolyte under the application of a very low gate voltage (V G < 1 V). The measured drain current (I D ) of the polymer channel between the source and drain contacts is therefore modulated through accumulation or depletion of charges throughout the bulk of the polymer. The corresponding transconductance (g m = ∂I D /∂V G ) is typically large (up to 2.0 mS for micrometer-scale devices [9] ), making OECTs an efficient ionto-electron transducers, capable of amplifying small chemical signals and with high signal-to-noise ratios. One important advantage of OECTs is that they can be fabricated from biocompatible organic materials, enabling an amiable interface with cells and tissues in aqueous environments (water-based electrolytes). [10] Also, their simple structure allows the potential for large-area and low-cost electronics through their facile fabrication processes such as printing and easy integration with microfluidic lab-on-a-chip applications. [11,12] The OECT transconductance, g m , is defined as follows: [13] µ ( )where d, W, and L are the thickness, width, and length of the channel respectively, µ is the carrier mobility, C* is the volumetric capacitance, and V th is the threshold voltage of the channel. In particular, the µC* figure of merit dictates the carrier and ionic transport and therefore affects the g m parameter. [14] In general, a good OECT channel material needs to have good electronic transport properties (high µ) and allows effective ion penetration from the electrolyte into active channel (high C*). The ability to have mixed ionic and electronic 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 ...

Aggregates -that is short-ranged ordered moieties in the solid-state of p-conjugated polymers -play an important role in the photophysics and performance of various optoelectronic devices. We have previously shown that many polymers change from a disordered to a more ordered conformation when cooling a solution below a characteristic critical temperature T c . Using in situ time-resolved absorption spectroscopy on the prototypical semiconducting polymers P3HT, PFO, PCPDTBT, and PCE11 (PffBT4T-2OD), we show that spincoating at a temperature below T c can enhance the formation of aggregates with strong intra-chain coupling. An analysis of their time-resolved spectra indicates that the formation of nuclei in the initial stages of film formation for substrates held below T c seems responsible for this. We observe that the growth rate of the aggregates is thermally activated with an energy of 310 meV, which is much more than that of the solvent viscosity (100 meV). From this we conclude that the rate controlling step is the planarization of a chain that is associated with its attachment to a nucleation center. The success of our approach for the rather dynamic deposition method of spin-coating holds promise for other solution-based deposition methods.So far, however, only limited approaches have been reported to induce aggregate formation in a controlled fashion, including slow solidification in marginal solvents, 26-29 control of entanglements and sonication, 30-34 and blending 35 -many using poly(3-hexyl thiophene) (P3HT) as model system and many relying on relatively time-consuming methodologies. Approaches to control the formation of aggregates during the solution deposition should ideally be based on considering thermodynamics of the solution as well as by taking the kinetics of film formation into account. 9 In particular with respect to the latter, several methods have been reported, such as varying the boiling point of the solvent, 9,21,36 varying Additional Supporting Information may be found in the online version of this article.

Additives are frequently used to enhance material properties. The addition of the processing additive 5‐aminovaleric acid iodide (5‐AVAI) into printed mesoscopic perovskite solar cells is shown to have a strong impact on the device performance and stability. Although it is difficult to understand the impact of 5‐AVAI as a processing additive by examining only the final thin films, the evolution of morphology with and without 5‐AVAI reveals that 5‐AVAI influences the crystallization behavior of the perovskite. In situ grazing incidence wide angle X‐ray scattering (GIWAXS) is performed to follow the perovskite formation within the printable all‐porous TiO2/ZrO2/carbon architecture and investigate the influence of 5‐AVAI on the perovskite crystallization within the scaffold. Using such time‐resolved measurements, the suppression of large crystalline perovskite grains is identified early in the fabrication process when 5‐AVAI is present, resulting in improved material backfilling. These observations highlight the importance of 5‐AVAI in the precursor solution for reliable fabrication of printed perovskite solar cells relying on the infiltration of a scaffold structure.

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