Including selenium atoms to the electron-accepting molecules in natural photo voltaic cells can both assist or hinder them, relying on precisely the place within the molecule the selenium sits, based on a computational research by researchers at China’s Nationwide Middle for Nanoscience and Know-how.
The crew’s calculations discovered that selenium positioned within the interior or outer components of the molecule’s fused-ring core lowered a amount referred to as reorganization power, which is linked to wasted power. Selenium positioned on the molecule’s central benzothiadiazole unit raised it as an alternative. The work, printed in Science China Chemistry and described in a launch from Science China Press on 4 November 2026, is totally theoretical. No photo voltaic cells had been constructed or examined, and no system effectivity is reported.
Why selenium is used in any respect
Natural photo voltaic cells use carbon-based molecules to show mild into electrical energy. The research focuses on the acceptor, the molecule that takes up electrons, and particularly on a category often known as non-fullerene acceptors.
In accordance with the discharge, swapping selenium atoms into these acceptors is a vital technique for bettering natural photo voltaic cell efficiency and slicing power loss, as a result of selenium modifications the molecules’ power ranges and the way in which they pack collectively. Selenium can also be a heavy atom, and that brings a second impact. It modifications how strongly the motion of electrons is tied to the vibrations of the molecule’s atoms, often known as electron-vibration coupling.
That coupling feeds into reorganization power. When a molecule good points, loses or passes on power or cost, its atoms shift into a brand new association, and reorganization power is the price of that shift. Below Marcus-Levich-Jortner concept, a framework for describing how briskly cost and power transfer between molecules, a smaller reorganization power helps preserve power losses down. The discharge says the impact of including selenium on reorganization power had not been studied systematically.
How the research labored
The researchers modelled acceptors based mostly on a molecule referred to as Y6. They positioned a single selenium atom in certainly one of three sorts of place: the central benzothiadiazole unit, or interior or outer positions of the fused-ring core. Additionally they modelled variations with two and 4 selenium atoms.
Reorganization energies had been calculated with density useful concept, a quantum-chemistry methodology for understanding the behaviour of electrons in molecules. The crew then estimated how briskly key processes would run utilizing a semiclassical model of the Marcus-Levich-Jortner framework, which accounts for the quantum nature of high-frequency molecular vibrations.
The calculations adopted three steps that matter inside a photo voltaic cell. In exciton power switch, the packet of power created when mild is absorbed strikes between molecules. In electron switch, that power is transformed into separated prices. In cost recombination, these separated prices come again collectively and their power is misplaced earlier than it may be collected as present.
What the calculations present
Place was decisive. Selenium on the central benzothiadiazole unit elevated reorganization energies for all three steps. Selenium at interior or outer core positions considerably diminished them, which within the mannequin suppresses exciton decay, helps electron switch and minimises non-radiative cost recombination, during which the power is misplaced with out being given off as mild.
The interior and outer positions did equally nicely at serving to excitons cut up into prices, however every had a special power. Outer substitution favoured step one, exciton power switch. Internal substitution was higher for the next electron switch step and for suppressing recombination.
Including extra selenium elevated the advantages, slicing the calculated cost recombination price by as much as 20%. The crew noticed comparable results in a second household of acceptors, the Qx sequence, which the authors say confirms the method applies broadly.
What it does and doesn’t imply
The discharge says the work establishes a rational design precept for high-performance natural photo voltaic cell supplies. In sensible phrases, it affords chemists a information on the place selenium ought to and mustn’t go when designing new acceptor molecules.
The bounds are essential. Each outcome comes from laptop fashions of particular person molecules. The 20% determine is a calculated discount in a recombination price, not a measured achieve within the effectivity of a working photo voltaic cell. Whether or not the expected results survive in actual supplies, and whether or not they would result in higher gadgets, must be examined by making and measuring these supplies.
