Polymer/fullerene solar cells are printed on paper using a combination of gravure and flexographic printing techniques. The printed paper photovoltaic cells are free from expensive electrodes made with indium–tin oxide, silver, or gold. Oxidized zinc film is used as the electron‐collecting layer.

No abstract

Lightweight, biodegradable, and inexpensive materials are desirable to enable low-cost photovoltaics. Paper fulfills these requirements and is compatible with standard roll-to-roll printing processes. Here we report 4% efficient organic solar cells fabricated on paper substrates with a zinc-coating acting as the back contact and evaporated MoO3/Ag/MoO3 semitransparent top electrodes. We demonstrate that the rough surface of paper does not preclude its use in high-efficiency organic photovoltaics.

No abstract

Mechanical strain energies in the form of movements/vibrations caused by human, machine or wind are available all around us in large quantities. A substantial amount of this renewable energy can be harvested by using piezoelectric devices. [ 1 ] Various piezoelectric energy harvesting devices (PEHDs) have been reported, mainly targeting small area applications. For example, small area PEHDs are effi cient enough to harvest substantial quantity of biological energy by human movement or by body bending. [ 2 ] According to a recent report, a mixture of BaTiO 3 nanoparticles and carbon nanotubes dispersed in a polymer matrix can generate up to 3.2 V. [ 3 ] BaTiO 3 thin fi lm based nanogenerators have been reported with an output voltage of 1.0 V and a current density of 0.19 μ A cm -2 . [ 4 ] A hybrid nanogenerator based on ZnO nanowire/poly(vinylidene fl uoride-trifl uorethylene) has been reported with output voltage, current density and power density of 0.1 V, 10 nA cm -2 and 16 μ W cm -3 , respectively. [ 5 ] Piezoelectric power generation from ZnO fi lm can be enhanced 18-fold by an addition of a p-type semiconducting polymer on top of it. [ 6 ] All these PEHDs are developed to harvest mechanical strain energy only from small areas. However, PEHDs can be used to harvest mechanical strain energy available on larger areas too. For example, PEHDs placed on a fl oor can generate energy when people walk over it. A large area sheet of PEHD in the form of a fl ag can be hung outside to harvest energy from wind. Production of large area PEHDs requires a method that can produce them in a cost effective manner with a high production speed. Roll-to-roll printing techniques, i.e., gravure, fl exography, offset and screen, can be effectively used to produce PEHDs for large area applications. These are wellestablished production techniques, available all over the world for printing applications. An advantage of fl exography printing is that it is a relatively inexpensive printing process, used mostly for package printing. For a larger area printing, which does not require a high resolution, it is a suitable production technique. In the last decade many innovative electronic components have been developed by using roll-to-roll printing methods. [7][8][9] Recently, our group has reported printed organic solar cells on a roll of paper by using gravure and fl exographic printing methods. [ 10 ] We also have reported piezoelectric loudspeakers printed by fl exography on a paper substrate. [ 11 ] Here, we report on a PEHD that is fully printed by the fl exographic printing method in ambient conditions. Although lead zirconate titanate (PZT) is one of the best piezoelectric materials, its application in energy harvesting is limited because of its mechanical rigidity. Recently, many approaches have been made to develop fl exible PZT based PEHDs, i.e., PZT ribbons and PZT fi ber composite. [ 12,13 ] As PEHDs generate alternating currents (AC), they can not be used directly to run most of the electronic devices, which require DC current...