Organic and printed electronics technologies require conductors with a work function that is sufficiently low to facilitate the transport of electrons in and out of various optoelectronic devices. We show that surface modifiers based on polymers containing simple aliphatic amine groups substantially reduce the work function of conductors including metals, transparent conductive metal oxides, conducting polymers, and graphene. The reduction arises from physisorption of the neutral polymer, which turns the modified conductors into efficient electron-selective electrodes in organic optoelectronic devices. These polymer surface modifiers are processed in air from solution, providing an appealing alternative to chemically reactive low-work function metals. Their use can pave the way to simplified manufacturing of low-cost and large-area organic electronic technologies.

Silicon photodiodes are the foundation of light-detection technology; yet their rigid structure and limited area scaling at low cost hamper their use in several emerging applications. A detailed methodology for the characterization of organic photodiodes based on polymeric bulk heterojunctions reveals the influence that charge-collecting electrodes have on the electronic noise at low frequency. The performance of optimized organic photodiodes is found to rival that of low-noise silicon photodiodes in all metrics within the visible spectral range, except response time, which is still video-rate compatible. Solution-processed organic photodiodes offer several design opportunities exemplified in a biometric monitoring application that uses ring-shaped, large-area, flexible, organic photodiodes with silicon-level performance.

Solar energy is potentially the largest source of renewable energy at our disposal, but significant advances are required to make photovoltaic technologies economically viable and, from a life-cycle perspective, environmentally friendly, and consequently scalable. Cellulose nanomaterials are emerging high-value nanoparticles extracted from plants that are abundant, renewable, and sustainable. Here, we report on the first demonstration of efficient polymer solar cells fabricated on optically transparent cellulose nanocrystal (CNC) substrates. The solar cells fabricated on the CNC substrates display good rectification in the dark and reach a power conversion efficiency of 2.7%. In addition, we demonstrate that these solar cells can be easily separated and recycled into their major components using low-energy processes at room temperature, opening the door for a truly recyclable solar cell technology. Efficient and easily recyclable organic solar cells on CNC substrates are expected to be an attractive technology for sustainable, scalable, and environmentally-friendly energy production.

Over the past several years, great progress has been made in the development of organic fi eld-effect transistors (OFETs). Prototypes of electronic devices such as drivers for fl at-panel displays, [ 1 ] complementary circuits, [ 2 , 3 ] radio-frequency identifi cation tags, [ 4 ] and chemical or biological sensors [ 5 , 6 ] have already been demonstrated. While charge-carrier mobility values have improved [ 2 , 3 , 7-9 ] with comparable values for both nand p -channel transistors, long-term environmental and operational stability remain two major issues that need to be resolved before OFETs can realize their full commercial potential.Recently, much effort has been devoted to improve the stability of OFETs. [10][11][12][13][14][15][16][17][18] For instance, to improve the environmental stability of OFETs, air-stable organic semiconductors have been synthesized [ 10 , 11 ] or encapsulation layers have been developed. [ 12 , 13 ] On the other hand, achieving operational stability is still a major challenge faced by OFETs as well as other fi eld-effect transistor (FET) technologies, such as those based on a -Si:H, poly-Si, and metal-oxide semiconductors. The operational stability of a FET is in general related to dipolar orientation and charge trapping/de-trapping events at all its critical interfaces and in the bulk of the semiconductor and gate dielectric. [14][15][16][17][18] The degradation of the performance of a FET during operation is refl ected by changes of its current-voltage characteristics that result from changes of mobility ( μ ), of threshold voltage ( V th ), or variations of the capacitance density ( C in ) of the gate dielectric. The dynamics of the physical and/or chemical mechanisms producing these changes, intrinsic or extrinsic, affect the performance of a FET on different time scales. [ 14 ] The stability of a FET is determined by the total effects produced by several physical and/or chemical processes, but in general, one tends to dominate over the others. This has caused current approaches to improve the stability to focus on mitigating individual processes. [15][16][17][18] Furthermore, the stability of OFETs has been primarily evaluated in devices with a bottom-gate geometry. OFETs with a top-gate geometry are relatively rare because the choice of gate dielectric material is limited since its deposition can potentially damage the organic semiconductor layer underneath. The use of an amorphous fl uoropolymer, CYTOP, has provided an attractive strategy for the realization of top-gate OFETs. This is because CYTOP has an excellent chemical stability, is highly hydrophobic, and dissolves in fl uorinated solvents that are orthogonal to most organic semiconductor materials. [ 8 , 16 , 19-22 ] However, CYTOP-based OFETs usually operate at high voltages because of its low dielectric constant and it is diffi cult to reliably reduce its thickness while maintaining a high device yield. [ 23 ] Hence, there is a need for high capacitance density gate insulators that have good stability and simulta...

Solution-based electrical doping protocols may allow more versatility in the design of organic electronic devices; yet, controlling the diffusion of dopants in organic semiconductors and their stability has proven challenging. Here we present a solution-based approach for electrical p-doping of films of donor conjugated organic semiconductors and their blends with acceptors over a limited depth with a decay constant of 10-20 nm by post-process immersion into a polyoxometalate solution (phosphomolybdic acid, PMA) in nitromethane. PMA-doped films show increased electrical conductivity and work function, reduced solubility in the processing solvent, and improved photo-oxidative stability in air. This approach is applicable to a variety of organic semiconductors used in photovoltaics and field-effect transistors. PMA doping over a limited depth of bulk heterojunction polymeric films, in which amine-containing polymers were mixed in the solution used for film formation, enables single-layer organic photovoltaic devices, processed at room temperature, with power conversion efficiencies up to 5.9 ± 0.2% and stable performance on shelf-lifetime studies at 60 °C for at least 280 h.

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Organometal halide perovskites have shown excellent optoelectronic properties and have been used to demonstrate a variety of semiconductor devices. Colorful solar cells are desirable for photovoltaic integration in buildings and other aesthetically appealing applications. However, the realization of colorful perovskite solar cells is challenging because of their broad and large absorption coefficient that commonly leads to cells with dark-brown colors. Herein, for the first time, we report a simple and efficient strategy to achieve colorful perovskite solar cells by using the transparent conducting polymer (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS) as a top electrode and simultaneously as an spectrally selective antireflection coating. Vivid colors across the visible spectrum are attained by engineering optical interference effects among the transparent PEDOT:PSS polymer electrode, the hole-transporting layer and the perovskite layer. The colored perovskite solar cells display power conversion efficiency values from 12.8 to 15.1% (from red to blue) when illuminated from the FTO glass side and from 11.6 to 13.8% (from red to blue) when illuminated from the PEDOT:PSS side. The new approach provides an advanced solution for fabricating colorful perovskite solar cells with easy processing and high efficiency.

We report on a systematic study of solvent and polymer matrix effects on the phase segregation behavior of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) blends incorporated into two different amorphous polymer matrices, poly (a-methyl styrene) and poly (triarylamine), and using two solvents, chlorobenzene and tetralin. Optical microscopy, X-ray diffraction analyses, and optical absorption measurements are used to evaluate the film morphology, crystallinity, and optical density, respectively. These analyses are correlated with the extent of vertical segregation of TIPS-pentacene, as observed for the blended films by depth-profile XPS analyses. The microstructure and vertical phase segregation of TIPS-pentacene in blend films are found to be strongly influenced by the choice of solvent. Tetralin, a solvent with a high boiling temperature, was found to be more desirable for achieving distinct phase segregation/crystallization of TIPS-pentacene in blend films and best performance in OFETs with a dual-gate geometry. The electrical properties of top and bottom channels were consistent with the morphological characterization and OFETs processed from tetralin showed higher mobility values than those from chlorobenzene. Further modification of the annealing conditions in the TIPS-pentacene/PTAA/tetralin ternary system led to top-gate OFETs with mobility values up to 2.82 cm 2 /Vs.