Fully printed origami thermoelectric generators for energy-harvesting

Energy-harvesting from low-temperature environmental heat via thermoelectric generators (TEG) is a versatile and maintenance-free solution for large-scale waste heat recovery and supplying renewable energy to a growing number of devices in the Internet of Things (IoT) that require an independent wireless power supply. A prerequisite for market competitiveness, however, is the cost-effective and scalable manufacturing of these TEGs. Our approach is to print the devices using printable thermoelectric polymers and composite materials. We present a mass-producible potentially low-cost fully screen printed flexible origami TEG. Through a unique two-step folding technique, we produce a mechanically stable 3D cuboidal device from a 2D layout printed on a thin flexible substrate using thermoelectric inks based on PEDOT nanowires and a TiS2:Hexylamine-complex material. We realize a device architecture with a high thermocouple density of 190 per cm² by using the thin substrate as electrical insulation between the thermoelectric elements resulting in a high-power output of 47.8 µWcm−² from a 30 K temperature difference. The device properties are adjustable via the print layout, specifically, the thermal impedance of the TEGs can be tuned over several orders of magnitudes allowing thermal impedance matching to any given heat source. We demonstrate a wireless energy-harvesting application by powering an autonomous weather sensor comprising a Bluetooth module and a power management system

Understanding the angle-independent photon harvesting in organic homo-tandem solar cells

The effective device photo current of organic tandem solar cells is independent of the angle of light incidence up to 65°. This feature renders these devices particularly suitable for stationary applications where they receive mainly indirect light. In a combined experimental and simulative study, we develop a fundamental understanding of the causal absorption and charge generation mechanisms in organic homo-tandem solar cells. A 3-terminal tandem device architecture is used to measure the optoelectronic properties of both subcells individually. The analysis of the angle dependent external quantum efficiencies of the subcells and the tandem device reveal an internal balancing of the wavelength dependent subcell currents elucidating the low sensitivity of the tandem device properties on the angle of incidence

Enhanced thermal stability of organic solar cells comprising ternary D-D-A bulk-heterojunctions

Organic solar cells: Polymer mixtures enhance the thermal stability Organic solar cells increase their lifetime by adding another polymer component, paving the way towards commercialization. A team led by Alexander Colsmann at Karlsruhe Institute of Technology, Germany conducted systematic spectroscopic investigations and device characterizations to demonstrate that the degradation of PTB7-Th: PC61BM solar cell can be efficiently suppressed by incorporating the near infrared-absorbing polymer PDTP-DFBT. Upon harsh thermal stress at 120 °C for 2 h, the ternary solar cells show only a minor relative deterioration of 10% with a high power conversion efficiency of 6%. This work reveals the importance of a third component to lock the phase conformation of the polymer and fullerene domains. This is a key step for the thermally stable power output thus the commercialization of the organic solar cells

Manuel Sacristán at the Onset of Ecological Marxism after Stalinism

Thirty-one years ago, in 1985, Manuel Sacristán died in Barcelona at the age of 59. After the publication in 2014 of a volume with some of his writings translated into English (Llorente 2014), it is time to help non-Spanish-speaking readers to know more about him. Yet it is not easy to explain to generations born after the fall of the Berlin Wall in 1989 that Manuel Sacristán was a most important Marxist philosopher and at the same time one of the few pioneers introducing political ecology and antinuclear peace movement during the last quarter of the 20th century in Spain. Many people believe that Marxism, environmentalism and pacifism are views that exclude each other. Most of what has been said and done on behalf of Marxism since Stalin took over the leadership of the Communist Party of the USSR in the 1930s, up to its dissolution in 1991, contributes to sustaining this belief. The fast industrialization of the Old Russian Empire undertaken by the Soviet State was nowhere near taking into account ecological sustainability. Its socio-environmental impact turned out to be comparable or even worse than the ones caused by capitalist industrialization