In order to battle climate change and continue increasing quality of life worldwide, huge amounts of renewable energy will be necessary. The world consumed 15 TW of energy in 2004, of which 7% was supplied by renewable sources. If current carbon levels and our increasing quality of life were to be sustained, approximately 15 TW would need to be supplied by renewable sources by 2030. Solar energy has the largest potential of all renewable energy sources to meet this need. Enough energy falls on the earth’s surface every hour to meet the entire world energy demand for a year. Therefore, our group is focused on improving the methods of harnessing solar power in order to meet the energy challenges of the 21st century.
The Solar Energy Group focuses on the fabrication of high efficiency solution processed solar cells. Using colloidal nanoparticle inks or molecular precursors, solar cells can be fabricated from solution based methods such as spin-coating, doctor blading, inkjet printing, or spray coating. The solution based method forgoes the typical high vacuum processing needed for semiconductor manufacturing, potentially leading to significantly reduced manufacturing costs.
In the pursuit of driving down the cost of manufacturing photovoltaic devices, we have developed a solution based route to fabricate high efficiency solar cells.
- The process starts by one of two methods: Colloidal Inks/Solutions, or Molecular Precursors. Colloidal solutions are made by synthesizing nanocrystals of the absorber layer for a given materials system. The nanocrystals are washed and suspended in a solvent. The molecular solution route bypasses the need for nanocrystal synthesis, where precursor materials are directly dissolved in solutions and are later dried and reacted directly on the substrate.
- Next, a film is deposited by a number of methods including doctor blading, spin coating, inkjet printing, and spray coating. Remaining solvent is typically removed by a heating step.
- The precursor film is now complete. At this stage the absorber layer material is typically formed into a film, however the size and density of grains is usually insufficient to make a device.
- The precursor films are subjected to a high temperature annealing step using a furnace. This heat treatment aids in grain growth and densification of the film.
- With the absorber layer complete, the remaining layer of the device can be deposited, typically CdS, ZnO and/or ITO. Finally grids are deposited on the top face and the device is now complete.
- In the last step, we are able to fully characterize our device using a number of electrical characterization techniques available in our labs.