Improvements to the efficiency of photovoltaics lowers the cost of solar electricity, as higher efficiency causes overhead costs to decrease. In this talk, I will discuss how optical design considerations, such as surface texturing and back mirror design, are crucial to achieving efficiencies that come close to thermodynamic limits. 

In a solar cell at open circuit voltage, ideally, all absorbed photons are re-emitted out the front surface. A back reflector is important to obtaining high efficiency, as it suppresses photon emission out the back surface. I will show how the back mirror concept can be extended to the sub-cells of a multijunction cell, with the use of air gaps as “intermediate” reflectors. The implementation of intermediate reflectors in a 4-junction cell has led to a record-breaking efficiency of 38.8%.

Surface texturing of solar cells also helps photon emission out the front surface. Inverse optical design is used to find optimal 3D surface textures for sub-wavelength thick solar cells. To conclude the talk, I will explore how inverse optical design can help us create imaging systems for maximum information collection in biomedical applications.