Friday, September 22, 2023

Researchers achieve breakthrough efficiency with organic solar cells

Organic solar cells (OSCs), also known as polymer solar cells, have attracted widespread attention and are considered one of the most promising clean and renewable energy candidates due to their unique merits of lightweight, flexible, and cost-efficient manufacturing with roll-to-roll processing techniques. Recently, with the emergence of non-fullerene acceptors (NFAs), OSCs’ power conversion efficiencies (PCEs) have exceeded 18%.

A team of researchers from The Hong Kong Polytechnic University (PolyU) has invented a new technique to achieve a breakthrough power-conversion efficiency of 19.31% with organic solar cells. The improved efficiency of over 19% constitutes a record for binary OSCs with one donor and one acceptor in the photoactive layer.

This remarkable binary OSC efficiency will help enhance the applications of these advanced solar energy devices.

To achieve this, researchers developed a non-monotonic intermediate state manipulation (ISM) strategy for state-of-the-art organic solar cells by employing 1,3,5-trichlorobenzene as a crystallization regulator. The new strategy manipulates the bulk-heterojunction (BHJ) OSC morphology and simultaneously optimizes the crystallization dynamics and energy loss of non-fullerene OSCs.

It promotes the formation of more ordered molecular stacking and favorable molecular aggregation. As a result, the excessive aggregation of non-fullerene acceptors is avoided, and researchers achieved efficient organic solar cells with reduced undesirable non-radiative recombination loss. The non-radiative recombination lowers the light generation efficiency and increases the heat loss.

“Challenges in research came from the existing additive-based benchmark morphology control methods, which suffer from non-radiative recombination loss, thus lowering the open-circuit voltage due to excessive aggregation,” said lead researcher Prof. Li Gang.

The research team took about two years to devise a non-monotonic ISM strategy for increasing the OSC efficiency and lowering the non-radiative recombination loss. “The new finding will make OSC research an exciting field, and this will likely create tremendous opportunities in applications like portable electronics and building-integrated PVs,” Li said.

They say a new door will open when low-cost single-junction OSCs can achieve a PCE of over 20%, along with more stable performance and other unique advantages such as flexibility, transparency, stretchability, low weight, and tuneable color.

“The latest study shows a record low non-radiative recombination loss of 0.168 eV in a binary OSC with a PCE of over 19%. This is a very encouraging result for the long-standing research on OSCs that I have conducted over the past two decades. We have already achieved better OSC efficiency, and this will subsequently help accelerate the applications of solar energy,” Li said.

Journal reference:

  1. Jiehao Fu, Patrick W. K. Fong, Heng Liu, Chieh-Szu Huang, Xinhui Lu, Shirong Lu, Maged Abdelsamie, Tim Kodalle, Carolin M. Sutter-Fella, Yang Yang, and Gang Li. 19.31% binary organic solar cell and low non-radiative recombination enabled by a non-monotonic intermediate state transition. Nature Communications, 2023; DOI: 10.1038/s41467-023-37526-5