Solar cell
A solar cell also called photovoltaic cell or photoelectric cell is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect. Improvements were slow but the only widespread use was in space applications where their power-to-weight ratio was higher than any competing technology.
Photovoltaic cells are made of semiconductors such as silicon. Basically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material and transferred to the semiconductor. The energy knocks electrons loose, allowing them to flow freely creating electricity.
Conventional crystalline silicon solar panels are expensive and inefficient. One way to increase the efficiency of solar cells is to use semiconductor nanoparticles, or quantum dots.
Semiconductor quantum dots
Researchers so far had only succeeded in creating such photo excited electron-hole pairs inside quantum dots. This is not very useful for real solar cells in which electron and holes need to be able to move freely throughout the entire sample. Only then can they create an electrical current that can be collected at an electrode.
Researchers at the Delft University of Technology in the Netherlands have shown for the first time that photo excited electrons can move freely in layers of linked semiconductor quantum dots. The new finding will be important for making cheap and efficient solar cells from these materials.
Due to avalanche effect a single photon can excite several electrons at the same time in a sample compared to conventional solar cells which can excites only one electron on incidence of light particle. In theory, the efficiency of cells made from these materials can reach 44%.
Free electron transport
Researchers have shown that electron-hole pairs can move as free charges between dots when these semiconductor nanoparticles are very densely clustered together while remaining separate using small spacer molecules. The arrangement means that the dots. The nanoparticles are so close to each other that in this arrangement every single light particle that is absorbed by the solar cell results in the generation of mobile electrons and holes. Since there are many of these electrons and holes, solar cells made of semiconductor nanoparticles could be very efficient.
The semiconductor nanoparticles behave like atomic crystals when the crystals are brought very close together that the electronic properties of nano crystals films are as good as those of conventional semiconductors. Also the electronic properties can be controlled by controlling the distance between the nano crystals. The researchers say that all the photo excited electrons produced can move freely through the material and that they can be collected in a solar cell. These solar cells can thus be made very simply and have a large photo voltage since energy is not wasted.