New electrode coating boosts performance of a photovoltaic cell

A KAUST led study has revealed that a single-molecule layer electrode coating can boost the performance of an organic photovoltaic cell.

The investigation has identified that the layer enhances the organic photovoltaic cell by boosting the electrical charge into an electrode – far exceeding the best traditional material, with this innovation potentially helping to advance devices designed around organic molecules, such as light-emitting diodes and photodetectors.

Organic photovoltaic cells work by employing a light-absorbing layer of carbon-based molecules, whereas conventional photovoltaic cells use crystalline silicon to harvest light. Currently, organic photovoltaic cells are surpassed in performance by silicon ones; however, novel printing techniques may make them a more economically viable alternative.

As light enters a photovoltaic cell, a negative electron is released by the energy creating a positive gap in its place – known as a hole; various materials then gather the holes and electrons, transporting them to an array of electrodes to produce an electrical current. To make the transportation of holes into an electrode more efficient in an organic photovoltaic cell, a material called PEDOT:PSS is utilised; however, this can harm the cell over time due to its acidity and being expensive.

To combat this issue, the researchers have developed a more efficient alternative to PEDOT:PSS, utilising a considerably thinner coating of Br-2PACz, a hole-transporting molecule that binds to an indium tin oxide (ITO) electrode, constructing a single-molecule layer. Br-2PACz achieves an impressive power conversion efficiency of 18.4%, surpassing the equivalent cell using  PEDOT:PSS, which displayed only 17.5%.

Yuanbao Lin, a PhD student and member of the study, said: “We were very surprised indeed by the performance enhancement. We believe Br-2PACz has the potential to replace PEDOT:PSS due to its low cost and high performance.”

Br-2PACz demonstrated a far superior increase to the efficiency of the cell in multiple facets, producing reduced electrical resistance, improved hole transport, and proficiency in allowing more light to permeate through the absorbing layer – with it also enhancing the light-absorbing layer itself due to the coating process.

The novel coating may even improve photovoltaic cell recyclability, with the team demonstrating that the ITO electrode could successfully be removed from the cell, stripped of its coating, and reused, whereas PEDOT:PSS makes the ITO surface much rougher, making its performance in another cell poor.

“We anticipate this will have a dramatic impact on both the economics of OPVs and the environment,” says Thomas Anthopoulos, who led the research.

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