Creating new, transparent conductive electrodes as an alternative to indium tin oxide is essential for implementing flexible solar cells on low-cost, opaque substrates such as steel foils. Such integration will also lead to the added value of steel foils for roofing applications.
IIT Kanpur scientists have developed organic solar cell gadgets that combine the organic polymer PTB7 as a donor and PCBM as an acceptor. Solar cells can convert a steel roof into an energy-producing device more efficiently than now. The MoO3/Au/MoO3 top electrode was used to fabricate the devices on opaque steel substrates. The study conducted in Prof. Ashish Garg’s lab at IIT Kanpur showed how multi-layer electrodes with MoO3/Au/MoO3 configuration can be integrated with organic solar cells.
MoO3 is an excellent choice as a capping layer for improved light coupling throughout the visible region, resulting in up to two times better transparency than an Au-only film. This improvement in the optical transmittance of MoO3/Au/MoO3 films, as studied by optical ellipsometry, suggests that higher refractive indices and lower extinction coefficients of MoO3 films compared to Au films make MoO3 films an excellent choice for capping layers.
In addition, as shown by XPS studies, the metal Mo+4 cations at the Au/MoO3 interface enhance the metallic character of the MoO3 film close to the interface, reducing the resistivity of the three-layer MoO3/Au/MoO3, which is nearly twice that of ITO.
Scientists noted, “Organic solar cell devices fabricated on opaque steel substrates with a MoO3/Au/MoO3 top electrode clearly showed an improvement in photovoltaic performance by 1.5 times, compared to that obtained with single-layer metal top electrodes.”
- L. Sowjanya Pali et al. Development of MoO3/Au/MoO3 Top transparent conductive electrode for organic solar cells on opaque substrates. Energy Technology. DOI: 10.1002/ente.202100689