Mgr Mathieu Turbiez

Poly(diketopyrrolopyrrole-terthiophene) for ambipolar logic and photovoltaics.

A new semiconducting polymer, PDPP3T, with alternating diketopyrrolopyrrole and terthiophene units is presented. PDPP3T has a small band gap of 1.3 eV and exhibits nearly balanced hole and electron mobilities of 0.04 and 0.01 cm(2) V(-1) s(-1), respectively, in field-effect transistors (FETs). By the combination of two identical ambipolar transistors, an inverter was constructed that exhibits a gain of approximately 30. When PDPP3T was combined with [60]PCBM or [70]PCBM in a 1:2 weight ratio, photovoltaic cells were made that provide a photoresponse up to 900 nm and an AM1.5 power conversion efficiency of 3.8 or 4.7%, respectively. In contrast to the almost constant FET mobility, the efficiency of the photovoltaic cells was found to be strongly dependent on the molecular weight of PDPP3T and the use of diiodooctane as a processing agent.

Efficient Solar Cells Based on an Easily Accessible Diketopyrrolopyrrole Polymer

A new easily accessible, high molecular weight, alternating dithieno-diketopyrrolopyrrolophenylene copolymer provides high electron and hole mobilities exceeding 0.02 cm2 V-1 s-1 in FETs and AM1.5 power conversion efficiencies of 4.6% and 5.5% in solar cells when combined with [60]PCBM and [70]PCBM. The performance of the solar cells strongly depends on the use of a processing agent.

Solution Processed Polymer Tandem Solar Cell Using Efficient Small and Wide bandgap Polymer:Fullerene Blends

Solution processed polymer tandem solar cells that combine wide and small bandgap absorber layers reach a power conversion efficiency of 7% in a series configuration. This represents a 20% increase compared to the best single junction cells made with the individual active layers and shows that the tandem configuration reduces transmission and thermalization losses in converting sunlight.

Small band gap polymers based on diketopyrrolopyrrole

New small band gap polymers incorporating diketopyrrolopyrrole units have been synthesized using Suzuki and Yamamoto polymerization. By alternating the electron-deficient diketopyrrolopyrrole units with different electron-rich aromatic segments, polymers were obtained with band gaps ranging from 1.24 to 1.77 eV in thin films. In field-effect transistors these polymers exhibit ambipolar charge transport with hole and electron mobilities up to 2.1 × 10−3 cm2/Vs and 1.6 × 10−4 cm2/Vs, respectively. The polymers were applied as electron donor in bulk heterojunction solar cells with [60]PCBM as electron acceptor to give a maximum power conversion efficiency of 1.7% under simulated standard solar light (AM1.5G, 100 mW/cm2). The morphology of the bulk heterojunction blend seems to limit the photovoltaic performance.

Predicting morphologies of solution processed polymer : fullerene blends

The performance of solution processed polymer:fullerene thin film photovoltaic cells is largely determined by the nanoscopic and mesoscopic morphology of these blends that is formed during the drying of the layer. Although blend morphologies have been studied in detail using a variety of microscopic, spectroscopic, and scattering techniques and a large degree of control has been obtained, the current understanding of the processes involved is limited. Hence, predicting the optimized processing conditions and the corresponding device performance remains a challenge. We present an experimental and modeling study on blends of a small band gap diketopyrrolopyrrole-quinquethiophene alternating copolymer (PDPP5T) and [6,6]-phenyl-C71-butyric acid methyl ester ([70]PCBM) cast from chloroform solution. The model uses the homogeneous Flory-Huggins free energy of the multicomponent blend and accounts for interfacial interactions between (locally) separated phases, based on physical properties of the polymer, fullerene, and solvent. We show that the spinodal liquid-liquid demixing that occurs during drying is responsible for the observed morphologies. The model predicts an increasing feature size and decreasing fullerene concentration in the polymer matrix with increasing drying time in accordance with experimental observations and device performance. The results represent a first step toward a predictive model for morphology formation.