Research

Functional Optoelectronic Materials for Energy

Monica Morales-Masis

The research focusses on the development, discovery and understanding of novel materials and thin films with functional optical and electrical properties. These materials and thin films find application in state of the art optoelectronic devices such as solar cells, OLEDs and transparent electronics.

 

 

Current research projects

High-Performance Transparent Conductive Oxides for Solar Cells

Transparent conductive oxides (TCOs) are essential in solar cells with resistive absorbers, such as the case of the silicon heterojunction solar cells and perovskite-based solar cells (1). To allow the maximum amount of sunlight into the cells, the front TCO should be transparent from the UV to the NIR; and to guarantee unhindered carrier extraction, the TCO should have high lateral conductivity and low contact resistance with the adjacent layers of the device. This is a challenge, as there is always a trade-off between transparency and conductivity.

Another challenge is the deposition of the TCO without damaging the exposed layers of the solar cells during growth. This motivates the search for gentle, soft-landing TCO deposition techniques that will ensure the formation of high-quality films without damaging the devices.  In this context, we are exploring pulsed-laser deposition (PLD) for low-damage fabrication of high-mobility TCOs for solar cells. The materials we are currently studying are zirconium-doped indium oxide (In2O3:Zr) and barium-stannate  (BaSnO3), both wide band-gap and high-mobility materials.

Novel p- and n-type Selective Contacts for Solar Cells

This research concerns the materials discovery of transparent p-type contacts.

Most TCOs and oxides known to date are n-type. The challenge for p-type conductivity in oxides originates from a highly-localized oxygen 2p valence band (low hole mobilities) and the positioning of the valence band well below the vacuum level (high ionization potentials) (1). Recent computational predictions indicate that a transition from a metal oxide to a metal oxychalcogenide or chalcogenide could solve the challenge of valence band delocalization, lowering the hole effective mass and increasing hole mobility. We are exploring this hypothesis by synthesizing the materials and characterizing the optoelectronic and compositional properties to determine the most promising compositions and optimize them for application as p-type contacts in solar cells.


Ref. (1) M. Morales-Masis et al. Adv. Electron. Mater. Vol. 3 (2017)