Solution processed polymer tandem solar cell using efficient small and wide band gap 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

Diketopyrrolopyrrole polymers as organic semiconductors and optical materials

The present invention relates to polymers comprising diketopyrrolopyrrole repeating units and their use as org. semiconductor in org. devices, esp. a diode, an org. field effect transistor and/or a solar cell, or a device contg. a diode and/or an org. field effect transistor, and/or a solar cell. The polymers according to the invention have excellent soly. in org. solvents and excellent film-forming properties. In addn., high efficiency of energy conversion, excellent field-effect mobility, good on/off current ratios and/or excellent stability can be obsd., when the polymers according to the invention are used in semiconductor devices or org. photovoltaic (PV) devices (solar cells). [on SciFinder (R)

A real-time study of the benefits of co-solvents in polymer solar cell processing

The photoactive layer of organic solar cells consists of a nanoscale blend of electron-donating and electron-accepting organic semiconductors. Controlling the degree of phase separation between these components is crucial to reach efficient solar cells. In solution-processed polymer–fullerene solar cells, small amounts of co-solvents are commonly used to avoid the formation of undesired large fullerene domains that reduce performance. There is an ongoing discussion about the origin of this effect. To clarify the role of co-solvents, we combine three optical measurements to investigate layer thickness, phase separation and polymer aggregation in real time during solvent evaporation under realistic processing conditions. Without co-solvent, large ¿fullerene-rich domains form via liquid–liquid phase separation at ~20 vol% solid content. Under such supersaturated conditions, co-solvents induce polymer aggregation below 20 vol% solids and prevent the formation of large domains. This rationalizes the formation of intimately mixed films that give high-efficient solar cells for the materials studie

Depositing fullerenes in swollen polymer layers via sequential processing of organic solar cells

Polymer solar cells are conventionally processed by coating a multicomponent mixture containing polymer, fullerene, solvent, and cosolvent. The photovoltaic performance strongly depends on the nanoscale morphology of the blend, which is largely determined by the precise nature of the solvent composition and drying conditions. Here, an alternative processing route is investigated in which the two active layer components are deposited sequentially via spin coating or doctor blading. Spin coating the fullerene from o-dichlorobenzene on top of the polymer provides virtually identical morphologies and photovoltaic performance. Using blade coating, the influence of the second-layer solvent for the fullerene derivative is investigated in further detail. Different aromatic solvents are compared regarding swelling of the polymer layer, fullerene solubility, and evaporation rate. It is found that while swelling of the polymer by the second-layer solvent is a necessity for sequential processing, the solubility of the fullerene derivative in this solvent has the strongest influence on solar cell performance. Homogeneous layers in which a sufficient amount of fullerene can infiltrate the polymer film can only be achieved when solvents are used that have a very high solubility for the fullerene and swell the polymer layer.\u3cbr/\u3

Poly(diketopyrrolopyrrole-terthiophene) for ambipolar logic and photovoltaics

(Chemical Equation Presented) 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 cm2 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 ~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