An international team of materials scientists from France, Russia and Kazakhstan found a way to boost the efficiency of organic solar cells. Organic solar cells are a third-generation photovoltaic technology using organic materials to harvest energy from light, outdoor as well as indoor. The solar cells are comprised of several layers including a photo-active layer and two electrode layers. The organic photovoltaic cells (OPVCs) are the form of polymer solar cells that produce electricity from sunlight using flexible polymers. Due to their higher band gaps, OPVCs have lower efficiencies when compared to inorganic photovoltaic cells.


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This process, known as fluorination, was previously shown to enhance polymer photovoltaic properties, but the mechanism was poorly understood. The new study clarifies the effect of fluorination on cell efficiency.


By experimenting with various polymer modifications, the team increased cell efficiency from 3. While this still falls short of the commercial silicon photovoltaics, organic solar cells massive gain in efficiency suggests that polymer-based cells organic solar cells a technology to be reckoned with.

Perhaps with further tweaks organic solar cells could outperform their polysilicon-based counterparts. It consists of a chain of repeating units shown in the left part of figure 1.

Organic solar cell

Each of them includes sulfur heterocycles—rings made of one sulfur and four carbon atoms—and hydrocarbon side chains with a branched structure.

The researchers produced a number of organic solar cells of this polymer to find which one has better photovoltaic properties.


They changed the structure organic solar cells adding fluorine atoms figure 1, right and varying the length of the side chains.

One polymer configuration proved to result in vastly superior properties. Namely, the cell efficiency and current output were several times higher.


The team then investigated the microscopic structure of the best-performing compound. X-ray analysis revealed polymer stacking to be more ordered.

Organic solar cells set 'remarkable' energy record - BBC News

Also, the molecules were characterized by higher charge carrier mobility, which means the material conducts electricity better. Mitigating the hole mobility bottleneck is key to further enhancing organic solar cells performance of OHJ's.

Single layer[ edit ] Fig organic solar cells Sketch of a single layer organic photovoltaic cell Single layer organic photovoltaic cells are the simplest form.

These cells are made by sandwiching a layer of organic electronic materials between two metallic conductors, typically a layer of indium tin oxide ITO with high work function and a layer of low work function metal such as Aluminum, Magnesium or Calcium.

The basic structure of such a cell is illustrated in Fig 2.

The difference of work function between the two conductors sets up an electric field in the organic layer. The potential created by the different work functions helps to split the exciton pairs, pulling electrons to the positive electrode an electrical conductor used to make contact with a non-metallic part of a circuit and holes to the negative electrode.

One device used polyacetylene Fig 1 as the organic layer, with Al and graphiteproducing an open circuit voltage of 0. A major problem with them is that the electric field resulting from the difference between the two conductive electrodes is organic solar cells sufficient to organic solar cells the excitons.

Often the electrons recombine with the holes without reaching the electrode. Bilayer[ edit ] Fig 3: Sketch of a multilayer organic photovoltaic cell.

Organic solar cells set 'remarkable' energy record

Bilayer cells contain two layers in between organic solar cells conductive electrodes Fig 3. The two layers have different electron affinity and ionization energiestherefore electrostatic forces are generated at the interface between the two layers.

Light must create excitons in organic solar cells small charged region for an efficient charge separation and collecting. The materials are chosen to make the differences large enough that these organic solar cells electric fields are strong, which splits excitons much more efficiently than single layer photovoltaic cells.

The layer with higher electron affinity and ionization potential is the electron acceptor, and the other layer is the electron donor. This structure is also called a planar donor-acceptor heterojunction. A layer of copper phthalocyanine CuPc as electron donor and perylene tetracarboxylic derivative as electron acceptor, fabricating a cell with a fill factor as high as 0.

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