Cambridge Team Uncovers Unexpected Quantum Behaviour in Non-Metal Organic Molecule

In a feat of organic-meets-electronic chemistry, scientists at the University of Cambridge have observed this quantum effect in an organic molecule that had long been considered incapable of such behaviour, a feature only special to metals. They found that a carefully engineered small-molecule organic semiconductor can deliver almost all of the photons above the device work function as useful current, as nearly 98 per cent of photo-generated carriers are transported out of the active layer and eventually result in photocurrent response.

Quantum Behaviour in Organics

As per Science Daily, organic molecules don't follow metal-like rules of electron interaction. In the majority of organic materials, electrons come in pairs, and the members of a pair don't “talk” to one another's buddies. But in P3TTM, there is an unpaired electron on each molecule that can interact with electrons on neighbouring molecules.

At high density, the molecules downshift to Mott-Hubbard behaviour, a behaviour familiar from inorganic materials. This enables electrons to hop from one molecule to another, generating charge separation in one material.

Implications for Solar Devices

To see if the idea works in practice, the researchers constructed a simple solar cell using P3TTM. The device was nearly ideal under light, gathering about the charges — most were converted to electricity.
By comparison, standard organic solar cells use two different materials, which, between them, limit the efficiency of the device. Apart from this simplification, there is one more exciting reason to celebrate these results of ours: They have, in fact, been around all along! On a more speculative note, the senior author, Sir Richard Friend, tied the discovery to pioneering ideas from Sir Nevill Mott, who theorised about how electrons would interact in solids.