Poly(3,:poly(styrene sulfonate) (PEDOT:PSS) has been widely used as a hole-conducting polymer in many optoelectronic devices including perovskite solar cells. However, its electrical and surface properties are not well controlled during the conventional ambient annealing. Herein, we apply the solvent posttreatments, including toluene vapor annealing and ethylene glycol (EG) washing, to modify not only the electrical conductivity and work function but also, importantly, the surface composition and morphology of PEDOT:PSS thin films. We show that annealing PEDOT:PSS films in a nonpolar toluene vapor environment results in a slightly enhanced electrical conductivity and increased work function while maintaining the surface composition and morphology. The CH 3 NH 3 PbI 3 perovskite solar cells using the toluene vapor-annealed PEDOT:PSS hole transporting layers (HTLs) yield a 31.8% increase in power conversion efficiency (PCE) from the control devices with the ambient conditionannealed PEDOT:PSS HTLs. All photovoltaic parameters are increased because of reduced trap states at the perovskite/HTL interface, as well as efficient and balanced charge generation, transport, and extraction rates. In contrast, washing PEDOT:PSS films with the polar EG solvent removes the PSS on the surface, increases the surface roughness, and dramatically increases the electrical conductivity by 5 orders of magnitude but slightly decreases the work function. Consequently, the CH 3 NH 3 PbI 3 perovskite solar cells with EG-washed PEDOT:PSS HTLs result in a 28.6% decrease in PCE from the control devices because of the increased trap states at the perovskite/HTL interface, which leads to an inefficient hole extraction. The charge accumulation at the perovskite/HTL interface also reflects in a serious hysteresis of J−V curves in the reversed bias region. This work highlights the importance of controlling both electronic and surface properties of PEDOT:PSS HTLs for the improvement of perovskite solar cell performance.

Hybrid organic–inorganic perovskite is one of the most promising candidates to replace state-of-art silicon to fabricate low cost solar cells. However, its instability, including intrinsic and operational instability, strongly hinders its real-life applications. Methylammonium (MA)-free, formamidinium (FA)-based perovskite doped by small A-site inorganic cations was developed to tackle the intrinsic instability issue, but the operational instability, especially against the applied electric field, induced by defect mediated ion migration remains a problem. In this work, we fabricate two types of MA-free perovskites, Rb0.05Cs0.1FA0.85PbI3 and Cs0.15FA0.85PbI3, and investigate the effect of Rb+ on the device performance and long-term stability. We find that even with incomplete incorporation, Rb+ cation can significantly improve the device performance. We reveal the defect-mediated cation and anion migration under electric field using cross-sectional secondary electron microscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry, and identify that Rb+ is more vulnerable compared to Cs+. By simply mixing the precursor solution before spin coating, we significantly reduce the defect states in both types of perovskite and improve the device stability against an electric field. The modified precursor solution provides the devices with Rb0.05Cs0.1FA0.85PbI3 and Cs0.15FA0.85PbI3 active layers that retain 68% and 92% of their initial PCE, respectively, over 30 days under N2 protection.

Poly­(hydroxymethylated-3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT-MeOH:PSS) conducting polymers are synthesized and incorporated in inverted structured perovskite solar cells (PVSCs) as hole transport materials. The highest occupied molecular orbital of PEDOT-MeOH is lowered by adding a hydroxymethyl (−MeOH) functional group to ethylenedioxythiophene (EDOT), and thus, the work function of PEDOT-MeOH:PSS is increased. Additionally, hydrogen bonding can be formed among EDOT-MeOH monomers and between EDOT-MeOH monomers and sulfate groups on PSS, which promotes PEDOT-MeOH chain growth and enhances PSS doping. The electronic, microstructural, and surface morphological properties of PEDOT-MeOH:PSS are modified by changing the amounts of PSS and the ferric oxidizing agent used in the polymerization and by adding ethylene glycol in the postsynthesis treatment. The PVSCs based on ethylene-glycol-treated PEDOT-MeOH:PSS overperform the PVSCs based on commercial PEDOT:PSS because of the better energetic alignment and the enhancement of PEDOT-MeOH:PSS electrical conductivity. This work opens the way to develop new hole transport materials for highly efficient inverted PVSCs.

Poly­(3,4-ethylenedioxythiophene) (PEDOT) conducting polymer synthesized via oxidative chemical polymerization in the presence of polyelectrolyte poly­(styrenesulfonate) (PSS) can form water-dispersible conductive ink and has broad applications. However, the lack of functionality of PEDOT hinders the broader application of PEDOT:PSS. In this work, we introduced a hydroxymethyl (−MeOH) and a chloromethyl (−MeCl) functional group to the oxyethylene ring of EDOT to obtain hydroxymethylated 3,4-ethylene­dioxythiophene (EDOT–MeOH) and chlorylmethylated 3,4-ethylene­dioxythiophene (EDOT–MeCl) monomer, respectively. We applied oxidative chemical polymerization to synthesize PEDOT–MeCl:PSS and PEDOT–MeOH:PSS as well as PEDOT:PSS. For EDOT, we found that adding base to neutralize acidic PSS has a significant effect on the dispersibility, surface morphology, and electrical conductivity (9.06 × 10–4–1.17 × 10–1 S/cm) of PEDOT:PSS. For functionalized EDOT, the repulsive force between EDOT–MeCl monomer and PSS counterion strongly hinders the oxidation and doping process, resulting in a product with well-dispersed PSS-doped PEDOT–MeCl and nondispersible sulfate-doped PEDOT–MeCl clusters, rough thin film, and electrical conductivity of 1.68 × 10–3 S/cm. The hydrogen bonding between EDOT–MeOH monomer and PSS counterion as well as among EDOT–MeOH monomers makes the polymerization and doping processes easy, yielding a well-dispersed, homogeneous product, smooth thin film, and electrical conductivity of 1.17 × 10–3 S/cm. This study sheds light on the polymerization of PEDOT with functional groups and provides a guideline for the synthesis of functionalized PEDOT conducting polymers with polyelectrolyte counterions using oxidative chemical polymerization.

Zeolite crystallization occurs by complex processes involving a variety of possible mechanisms. The sol gel media used to prepare zeolites leads to heterogeneous mixtures of solution and solid states with diverse solute species. At later stages of zeolite synthesis when growth occurs predominantly from solution, classical two-dimensional nucleation and spreading of layers on crystal surfaces via the addition of soluble species is the dominant pathway. At earlier stages, these processes occur in parallel with nonclassical pathways involving crystallization by particle attachment (CPA). The relative roles of solution- and solid-state species in zeolite crystallization have been a subject of debate. Here, we investigate the growth mechanism of a commercially relevant zeolite, faujasite (FAU). In situ atomic force microscopy (AFM) measurements reveal that supernatant solutions extracted from a conventional FAU synthesis at various times do not result in growth, indicating that FAU growth predominantly occurs from the solid state through a disorder-to-order transition of amorphous precursors. Elemental analysis shows that supernatant solutions are significantly more siliceous than both the original growth mixture and the FAU zeolite product; however, in situ AFM studies using a dilute clear solution with a lower Si/Al ratio revealed three-dimensional growth of surfaces that is distinct from layer-by-layer and CPA pathways. This unique mechanism of growth differs from those observed in studies of other zeolites. Given that relatively few zeolite frameworks have been the subject of mechanistic investigation by in situ techniques, these observations of FAU crystallization raise the question whether its growth pathway is characteristic of other zeolite structures.