In a solar cell, light generates opposite charges in the active layer. Opposite charges attract each other. So, the charges must then be separated as quickly as possible to keep them from recombining. Positive charges are driven by a built-in electric field to one metallic contact, while negative charges migrate in the opposite direction to another electrode.
Now, using a unique ultra-fast spectroscopic technique, scientists including researchers from Saudi Arabia have tracked the fate of charged pairs in an advanced type of solar cells. This technique allows real-time measurements of the separation distance of charges generated by light in the active layer of a solar cell.
The technique relies on the optical probing of the effective electric field experienced by a material. An external field is applied to the device and affects the absorption spectrum of materials that make up its photoactive layer.
An ultrashort laser pulse then generates charges. These charges begin to separate, inducing a counter electrical field that opposes the externally applied one. As a result, a decrease of the amplitude of the electroabsorption signal can be detected in real time with pico- to femto-second resolution.
The study creates a better understanding of the mechanisms of light-induced charge separation in this type of solar cells, which is necessary for designing more efficient solar cells, the researchers report in the 2 September 2016 online issue of Nature Communications.