Optoelectronics

Bulk-heterojunction polymer solar cells (BHJ-PSCs) 

Polymer solar cells (PSCs) are flexible, lightweight, and highly customizable, but their efficiency and stability is still lower than that of silicon-based cells. For this aim, our group describe molecular engineering strategies using Ir(III) complexes for enhancement of efficiency and stability of PSCs.

First, we developed customized energy transfer system by color-tuning of Ir(III) complexes, and then applied them to triplet-singlet energy transfer for enhanced performance of PSCs. Furthermore, to secure the molecular compatibility of the energy transfer system, we introduced amphiphilic nature in the Ir(III) complex, thereby allow them to perform the role of a surfactant at the donor/acceptor interface in active layer. As a result, our customized energy transfer system can be applied in various photo-active materials like as crystalline and amorphous polymers.

Second, we described electrical double layers (EDLs) system by incorporating ionic Ir(III) complexes for highly efficient and durable PSCs. Using the ionic Ir(III) complexes as charge transport layer, EDLs is formed in electrode surface, thereby enabling an improvement in charge extraction. In addition, strong absorption property for ultraviolet (UV) region protect the active layer from the intensive light, resulting in developing stable and durable PSC performance.

Finally, we developed a hydrogen bonding based molecular locking system using Ir(III) complexes, to overcome poor stability of PSC in outdoor environment. Formation of hydrogen bonding freezes the crystal structure of blended active layer, and enhances the durability of the devices as a result. Furthermore, optimized hydrogen bonding condition enhances the pi-pi stacking of active materials, resulting in enhanced charge transport.

We expected that these molecular engineering strategies open up a new avenue for the developments of highly stable and efficient polymer solar cells.

 

Keywords: polymer solar cell, Ir(III) complex, energy transfer, electrical double layer, molecular locking

 

1) H.T. Kim et al. ACS Energy Lett, 1, 991 (2016)

2) H.T. Kim et al. Scientific Reports,8, 16974 (2018)

 

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