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Tunable quantum dots for future solar cells

Researchers from the National Research Nuclear University «MEPhI» (Moscow Engineering Physics Institute) have derived the general principles of functioning photocells of a new type, the «solid» quantum dots. The new data will facilitate the creation of solar batteries based on this type of materials.
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Solar cells based on quantum dots is a cutting edge of modern solar energetics while the new study of Russian scientists may notably put forward the situation in this field.

Quantum dots are micro- and nanofragments of compounds with semiconductive properties. Their sizes are very small and typically given in nanometers implying that quantum effects play an essential role. As a result of these effects, a quantum dot can «grasp» a photon of solar light even if the dot material itself at normal conditions (in a larger particle) is not capable of capturing light. To ensure this property, the size of quantum dot should be close to the wavelength of the light which should be absorbed.

The main problem in the calculation of efficiency of such solar cells is that one can relatively easy estimate the probability of photon capture, but the evaluation of the efficiency of electron transfer (which are formed when photons enter a semiconductor) between quantum dots is a challenging task.

The authors of the new study have found out the working principles of a new type of photocells based on «solid» quantum dots obtained by deposition of colloid solutions. The new calculations have demonstrated that the probability of electron transfer and photon capture can be relatively easy estimated for assembled and non-assembled solid quantum dots.

The peculiarity of photocells based on quantum dots is the binding of separate dots by organic molecules, the ligands, which is essential to merge a photoelement plate into a single unit. The correct calculation of parameters of quantum dots based on any materials influences the choice of ligands and, consequently, the coefficient of efficiency of such solar cells. If the ligands provide a too wide gap, the output of a battery will be too low. By thoroughly choosing the ligands using calculations, one could avoid such problems. This implies that the new study may play a significant role in the broad application of the new class of materials.

The respective scholar article is published in the Journal of Physical Chemistry Letters.

Previously, the scientists from Switzerland and Germany have elaborated a technique of creating perovskite solar cells with a record-breaking efficiency of 20%.

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