High-Performing Polycarbazole Derivatives for Efficient Solution-Processing of Organic Solar Cells in Air

The application of conjugated materials in organic photovoltaics (OPVs) is usually demonstrated in lab-scale spin-coated devices that are processed under controlled inert conditions. Although this is a necessary step to prove high efficiency, testing of promising materials in air should be done in the early stages of research to validate their real potential for low-cost, solution-processed, and large-scale OPVs. Also relevant for approaching commercialization needs is the use of printing techniques that are compatible with upscaling. Here, solution processing of organic solar cells based on three new poly(2,7-carbazole) derivatives is efficiently transferred, without significant losses, to air conditions and to several deposition methods using a simple device architecture. High efficiencies in the range between 5.0 % and 6.3 % are obtained in (rigid) spin-coated, doctor-bladed, and (flexible) slot-die-coated devices, which surpass the reference devices based on poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT). In contrast, inkjet printing does not provide reliable results with the presented polymers, which is attributed to their high molecular weight. When the device area in the best-performing system is increased from 9 mm2 to 0.7 cm2, the efficiency drops from 6.2 % to 5.0 %. Photocurrent mapping reveals inhomogeneous current generation derived from changes in the thickness of the active layer

ITO Modification for Efficient Inverted Organic Solar Cells

We demonstrate a facile approach to designing transparent electron-collecting electrodes by depositing thin layers of medium and low work function metals on top of transparent conductive metal oxides (TCOs) such as ITO and FTO. The modified electrodes were fairly stable for months under ambient conditions and maintained their electrical characteristics. XPS spectroscopy data strongly suggested integration of the deposited metal in the TCO structure resulting in additional doping of the conducting oxide at the interface. Kelvin probe microscopy measurements revealed a significant decrease in the ITO work function after modification. Organic solar cells based on three different conjugated polymers have demonstrated state of the art performances in inverted device geometry using Mg- or Yb-modified ITO as electron collecting electrode. The simplicity of the proposed approach and the excellent ambient stability of the modified ITO electrodes allows one to expect their wide utilization in research laboratories and electronic industry

Nanostructured Organosilicon Luminophores for Effective Light Conversion in Organic Light Emitting Diodes

Full characterization of nanostructured organosilicon luminophores NOL4 and NOL5 based on the donor 2,2’-bithiophene and acceptor 1,4-bis(2,2′- bithiophene-5-yl)benzene units in dilute solutions and thin films by UV-Vis spectroscopy, DSC, TGA and X-ray techniques was reported. It was found that usage of these molecules as dopants (10–20 wt%) to the electroactive polyfluorene host in organic light-emitting devices (OLEDs) leads to the efficient spectral long wavelength shifting of the electroluminescence and an increase of the OLED performance as compared to the devices based on pristine polyfluorene, NOL4 and NOL5

Design of (X-DADAD)(n) Type Copolymers for Efficient Bulk Heterojunction Organic Solar Cells

We show that extended TBTBT structure (T = thiophene, B = benzothiadiazole) can be used as an electron-deficient building block for designing conjugated polymers with deeply lying HOMO energy levels and narrow band gaps. The first carbazole-TBTBT copolymer P2 demonstrated power conversion efficiencies exceeding 6% in bulk heterojunction solar cells in combination with advanced operational stability, unlike conventional donor polymers such as PTB7, PBDTTT-CF, etc

Design of (X-DADAD)_<i>n</i> Type Copolymers for Efficient Bulk Heterojunction Organic Solar Cells

We show that extended TBTBT structure (T = thiophene, B = benzothiadiazole) can be used as an electron-deficient building block for designing conjugated polymers with deeply lying HOMO energy levels and narrow band gaps. The first carbazole–TBTBT copolymer <b>P2</b> demonstrated power conversion efficiencies exceeding 6% in bulk heterojunction solar cells in combination with advanced operational stability, unlike conventional donor polymers such as PTB7, PBDTTT-CF, etc