Jason Seifter

Inverted Polymer Solar Cells Integrated with a Low‐Temperature‐Annealed Sol‐Gel‐Derived ZnO Film as an Electron Transport Layer

BHJ solar cells are typically fabricated with a transparent conductive anode (e.g. indium tin oxide, ITO), a low-work-function metal cathode (e.g., Al, Ca), and an active layer (a mixture of conjugated polymer and fullerene derivative) sandwiched between the anode and cathode. The BHJ layer and cathode dramatically affect the stability. In particular, the cathode is susceptible to degradation by oxygen and water vapor. Poly(3,4ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is often used as an anode buffer layer. Long-term stability is a problem because PEDOT:PSS is hygroscopic and acidic. [ 17–21 ]

High‐Efficiency Polymer Solar Cells Enhanced by Solvent Treatment

A significant enhancement of efficiency in thieno[3,4-b]-thiophene/benzodithiophene:[6,6]-phenyl C71-butyric acid methyl ester (PTB7:PC70 BM) solar cells can be achieved by methanol treatment. The effects of methanol treatment are shown in an improvement of built-in voltage, a decrease in series resistance, an enhanced charge-transport property, an accelerated and enlarged charge extraction, and a reduced charge recombination, which induce a simultaneous enhancement in open-circuit voltage (Voc), short-circuit current (Jsc), and fill factor (FF) in the devices.

High Performance Weak Donor–Acceptor Polymers in Thin Film Transistors: Effect of the Acceptor on Electronic Properties, Ambipolar Conductivity, Mobility, and Thermal Stability

We have studied the electronic, physical, and transistor properties of a family of donor-acceptor polymers consisting of diketopyrrolopyrrole (DPP) coupled with different accepting companion units in order to determine the effects of donor-acceptor interaction. Using the electronically neutral benzene (B), the weakly accepting benzothiadiazole (BT), and the strongly accepting benzobisthiadiazole (BBT), the accepting strength of the companion unit was systematically modulated. All polymers exhibited excellent transistor performance, with mobilities above 0.1 cm(2)V(-1)s(-1), even exceeding 1 cm(2)V(-1)s(-1) for one of the BBT-containing polymers. We find that the BBT is the strongest acceptor, enabling the BBT-containing polymers to be strongly ambipolar. The BBT moiety also strengthens interchain interactions, which provides higher thermal stability and performance for transistors with BBT-containing polymers as the active layer.

High‐Performance Ambipolar Transistors and Inverters from an Ultralow Bandgap Polymer

High mobility ambipolor organic thin-film transistors based on an ultralow bandgap polymer are presented together with their morphological and optical properties. Hole and electron mobilities of this polymer are of 1.0 cm(2) V(-1) s(-1) and 0.7 cm(2) V(-1) s(-1), respectively. The inverter based on two identical ambipolar transistors exhibits a gain around 35.

Molecular doping enhances photoconductivity in polymer bulk heterojunction solar cells

Addition of low concentrations (<1:100, dopant:donor) of a fluorinated p-type dopant, F4-TCNQ leads to a considerable enhancement of the photocurrent in PCDTBT:PC70 BM bulk heterojunction solar cells. As a result, the power conversion efficiency increases from 6.41% to 7.94 %.

Ambipolarity in Benzobisthiadiazole‐Based Donor–Acceptor Conjugated Polymers

A family of four new DA polymers, in which the acceptor moiety benzobisthiadiazole was paired with four different donor moieties, has been synthesized. Surpri-singly, all members of the family exhibit balanced ambipolar behavior, despite polymer to polymer mobilities varying from 10(-4) cm(2) V(-1) s(-1) to 10(-1) cm(2) V(-1) s(-1). Applications in single component CMOS integrated circuits are envisioned.

Ordered Polymer Nanofibers Enhance Output Brightness in Bilayer Light-Emitting Field-Effect Transistors

Polymer light emitting field effect transistors are a class of light emitting devices that reveal interesting device physics. Device performance can be directly correlated to the most fundamental polymer science. Control over surface properties of the transistor dielectric can dramatically change the polymer morphology, introducing ordered phase. Electronic properties such as carrier mobility and injection efficiency on the interface can be promoted by ordered nanofibers in the polymer. Moreover, by controlling space charge in the polymer interface, the recombination zone can be spatially extended and thereby enhance the optical output.

Transient Photocurrent Response of Small‐Molecule Bulk Heterojunction Solar Cells

Transient photocurrent measurements are used to investigate the effects of processing additives on charge transport in small molecule bulk heterojunction solar cells. The additive decreased carrier recombination rates and improved carrier mobility, both of which are beneficial to carrier extraction. Geminate recombination of charge transfer excitons is ruled out by the data.

Solution-processed pH-neutral conjugated polyelectrolyte improves interfacial contact in organic solar cells.

The intrinsic acidic nature of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole-transporting layer (HTL) induces interfacial protonation and limits the device performance in organic solar cells based on basic pyridylthiadiazole units. By utilizing a pH neutral, water/alcohol soluble conjugated polyelectrolyte CPE-K as the HTL in p-DTS(PTTh2)2:PC71BM solar cells, a 60% enhancement in PCE has been obtained with an increased V(bi), reduced R(s), and improved charge extraction. These effects originate from the elimination of interfacial protonation and energy barrier compared with the PEDOT:PSS HTL.

Observations of PDDTT subject to thermal treatment: correlation between performance and order.

We show that polybis(thienyl)thienodia-thiazolethiophene (PDDTT), a high-performance semiconducting polymer for photodetectors and field-effect transistors, has strong performance dependence on annealing temperature. An unprecedented increase of 3 orders of magnitude is observed in both transistor and photoconductive properties. XRD and AFM evidence points to increased ordering in PDDTT films with annealing. This correlation highlights the importance that order has in determining performance in PDDTT and has possible implications in the design of polymers.