Frameworks with metal nodes improve organic solar cell power conversion efficiency

The lightweight design and relatively cheap, easy manufacturing of organic photovoltaic cells are highly advantageous features. However, current organic frameworks have low power conversion efficiency (PCE). Researchers have sought to overcome organic material shortcomings by combining a 2-D organic material with metal nodes, reporting their findings in Applied Physics Letters.

The heterojunction solar cell analyzed here consists of secondary organic phthalocyanine (Pc) building blocks linked through zinc (Zn-Pc). Pc was a good candidate because it has ideal semiconductor properties and forms flat and rigid 2-D conformations by supramolecular self-assembly. The computational analysis employed density functional theory calculations to assess the physical and optoelectronic properties of the network. To tailor the performance, possible combination options were screened. This included assessing insertion of a benzene ring, heteroatom doping and interlayer stacking.

Some of the combinations had donor and accepter absorber gap and interface band alignments that met the requirements for an organic solar cell. The highest PCE achieved (14 percent) is the best recorded PCE for an organic photovoltaic cell, calculated from a blended bilayer solar cell. The researchers also simulated the feasibility of Zn-Pc framework chemical preparation and encourage experimentalists to attempt synthesis of the system.

“With a 2-D organic semiconductor you have a continuous framework, which gives you almost infinite possibility to tune the physical properties by chemical engineering,” said co-author Jijun Zhao. He explained that they are using this strategy to examine other 2-D organic materials for solar cells and other applications. For instance, a similar system can be used to optimize the magnetic and anisotropic energies of materials for magnetic storage at room temperature.

Source: “Self-assembly 2-D zinc-phthalocyanine heterojunction: An ideal platform for high efficiency solar cell,” by Xue Jiang, Zhou Jiang, and Jijun Zhao, Applied Physics Letters (2017). The article can be accessed at https://doi.org/10.1063/1.5005119 .