MEPhI scientists studied the features of photogeneration (the formation of mobile electrons and holes when absorbing light quanta) in organic semiconductors and described how its efficiency varies with temperature. In their opinion, this will help create more advanced organic photovoltaic devices, including solar panels. The research results were published in The Journal of Physical Chemistry Letters.

Disordered organic semiconductors are widely used today in electronics as LEDs. Scientists are actively exploring the possibilities of their use in thin-film transistors, photovoltaics, sensors, etc. The advantages of disordered organic semiconductors over other materials are flexibility, lightness, variety of properties, and the possibility of production using low-cost mass technology.

In disordered organic semiconductors, due to the small value of the dielectric constant, the absorption of a photon leads to the formation of pairs in which the electron and hole are separated in space, but are connected by the Coulomb interaction (the so-called “geminal pairs”). The probability of complete separation of such pairs determines the efficiency of photogeneration of free charge carriers - electrons and holes. Increasing the efficiency of photogeneration, in turn, is very important for the development of organic photovoltaic devices, for example, solar cells.

MEPhI scientists have developed an analytical model that explains the weak dependence of the probability of separation of geminate pairs on temperature, in agreement with experiment and Monte Carlo simulation data.

“The fact is that the diffusion of highly nonequilibrium (“hot”) charge carriers is anomalously strong and weakly depends on temperature in the initial time interval after pair formation due to energy disorder. We were able to estimate a key parameter of the model - the initial separation of the pair - which depends on the properties of the material. Previously, scientists determined it only by fitting it to experimental data,” said Vladimir Nikitenko, a professor at the Institute of Nanotechnologies in Electronics, Spintronics and Photonics at MEPhI.

According to the researchers, the results of the work will help simulate the photogeneration of charge carriers in organic semiconductors in order to increase its efficiency.

The work was supported by a grant from the Russian Science Foundation.