Material makes it possible to create ultra-thin solar cells(2)

To prevent recombination of electrons and holes, metallic electrodes can be used, through which the charge is sucked awayor a second material is added. “The holes move inside the tungsten diselenide layer, the electrons, on the other hand, migrate into the molybednium disulphide”, says Mueller. Thus, recombination is suppressed.

This is only possible if the energies of the electrons in both layers are tuned exactly the right way. In the experiment, this can be done using electrostatic fields. Florian Libisch and Professor Joachim Burgd?rfer provided computer simulations to calculate how the energy of the electrons changes in both materials and which voltage leads to an optimum yield of electrical power.

“One of the greatest challenges was to stack the two materials, creating an atomically flat structure,” says Mueller. “If there are any molecules between the two layers so that there is no direct contact, the solar cell will not work.” Eventually, this feat was accomplished by heating both layers in vacuum and stacking it in ambient atmosphere. Water between the two layers was removed by heating the layer structure once again.

Part of the incoming light passes right through the material. The rest is absorbed and converted into electric energy. The material could be used for glass fronts, letting most of the light in, but still creating electricity. As it only consists of a few atomic layers, it is extremely lightweight (300m² weigh only one gram), and very flexible. Now the team is working on stacking more than two layers; this will reduce transparency, but increase the electrical power.