No abstract

Transparent conductors (TCs) play a vital role in displays, solar cells, and emerging printed electronics. Here, we report a solution-processable n-doped organic conductor from copper-catalyzed cascade reactions in the air, which involves oxidative polymerization and reductive doping in one pot. The formed polymer ink is shelf-stable over 20 days and can endure storage temperatures from −20 to 65 °C. The optimized n-doped thin-film TC exhibits a low sheet resistance of 45 Ω/sq and a high transmittance (T 550 > 80%), which can rival indium tin oxide. The transparent organic conductor exhibits excellent durability under accelerated weathering tests (85 °C/85% RH). Furthermore, the n-doped polymer film can also function as an electrode material with a high volumetric capacity. When it is paired with p-doped PEDOT:PSS, a record-high coloration efficiency is obtained in a dual-polymer electrochromic device.

Solution-processed organic semiconductor layers on rough surfaces tend to vary widely in thickness, significantly hindering charge extraction in relevant optoelectronic devices. Herein, we report the photoactivated p-doping of hole-transporting material (HTM) to enhance hole extraction for (textured) perovskite/silicon tandem solar cells, making the device performance less sensitive to the variation of hole transport layer thickness. We used the ionic compound 4isopropyl-4′-methyldiphenyliodonium tetrakis(penta-fluorophenyl-borate) (DPI-TPFB) as a p-type dopant in poly(triaryl amine) (PTAA), which we used as the HTM. We observed that light soaking DPI-TPFB-doped PTAA shows approximately 22 times higher conductivity compared with an undoped PTAA film, which translated into an improved fill factor (FF) for tandem solar cells. Our tandem solar cells achieved an ∼80% FF and 27.8% efficiency and operated at their maximum power point for 200 h without loss of performance, in addition to retaining ∼83% of initial performance over a month of operation in an outdoor environment.

Chemical and electrochemical doping of π-conjugated polymers is an important aspect in determining the performance and enabling the operation of many organic electronic devices, from organic light emitting diodes and thermoelectrics to organic electrochemical transistors. In both chemical doping and electrochemical doping an ionized dopant or counterion is present along with the doped π-conjugated polymer. This dopant or counterion is not a benign spectator, rather, its presence can significantly impact the optical, electronic, and thermoelectric properties of the resulting material. Here, we investigate how counterion structure impacts the electrochemical doping ability, oxidation potential, ionization energy, and polaron absorbance of regioregular (rr) and regiorandom (rra) P3HT. We find that in most cases the anion has a small effect on the polymer oxidation potential, except for in the case of rr-P3HT with the large tetrakis[3,5-bis(trifluoromethyl)phenyl]borate anion. We propose that this large anion is excluded from the crystalline regions and thus the oxidation potential is similar to that of rra-P3HT. The anions also result in significant differences in polaron absorbance and ionization energies, thereby emphasizing the important role of the counterion in determining the optical and electronic properties of doped π-conjugated polymers.

will occur. Additionally, probing the DOS with high enough sensitivity to probe defect states is important, as these defect states often limit charge transport in semiconducting materials or serve as recombination centers in photovoltaics. [3,5,6] Recently, an electrochemical technique, energy-resolved electrochemical impedance spectroscopy (ER-EIS), was applied to measure the density of states of organic semiconductors (OSCs) with high sensitivity. [7][8][9][10][11] The detection of defect states using electrochemical methods is particularly relevant to understanding charge-carrier transport in organic electrochemical transistors (OECTs), which are of growing interest for neuromorphic computing, [12][13][14] biosensing, [15][16][17] and bioelectronics. [18][19][20] The IE and EA are typically measured using either photoemission spectroscopies, including ultraviolet and inverse photo emission spectroscopy (UPS and IPES, respectively), or extracted based on electrochemical methods, such as cyclic voltammetry, differential pulse voltammetry, or more recently ER-EIS. Here, we use IE and EA in place of the often-used highest occupied molecular orbital (HOMO) energy and lowest unoccupied molecular orbital (LUMO) energy, respectively, to be consistent with recommended terminology. [21] In photoemission spectroscopy, an electron is emitted into vacuum upon absorption of a photon with sufficient energy (UPS), and in inverse photoemission a photon is emitted upon acceptance Determining the relative energies of transport states in organic semiconductors is critical to understanding the properties of electronic devices and in designing device stacks. Futhermore, defect states are also highly important and can greatly impact material properties and device performance. Recently, energyresolved electrochemical impedance spectroscopy (ER-EIS) is developed to probe both the ionization energy (IE) and electron affinity (EA) as well as subbandgap defect states in organic semiconductors. Herein, ER-EIS is compared to cyclic voltammetry (CV) and photoemission spectroscopies for extracting IE and EA values, and to photothermal deflection spectroscopy (PDS) for probing defect states in both polymer and molecular organic semiconductors. The results show that ER-EIS determined IE and EA are in better agreement with photoemission spectroscopy measurements as compared to CV for both polymer and molecular materials. Furthermore, the defect states detected by ER-EIS agree with sub-bandgap features detected by PDS. Surprisingly, ER-EIS measurements of regiorandom and regioregular poly(3-hexylthiophene) (P3HT) show clear defect bands that occur at significantly different energies. In regioregular P3HT the defect band is near the edge of the occupied states while it is near the edge of the unoccupied states in regiorandom P3HT.