Have you ever thought about how a solar cell functions and operates? Its function is quite simple: converting sunlight to electricity. Its operation is quite rudimentary. Solar cell is a semiconductor. The primary characteristic of a semiconductor is the presence of a band-gap. This band-gap has a finite energy. In a simplistic view, when sunlight is incident on the solar cell, the carriers which are electrons and holes jump across the band-gap and when connected to a load causes a flow of current.
With such a simple concept, why is then this technology still at a mature startup stage? It turns out that silicon, the most abundant semiconductor has a band-gap which is not the best suited for converting the energy from the sun to electricity. Due to its nature of its band-gap, the physics of the carriers jumping across the band-gap results in a lot of wasted energy in the form of heat or thermal energy.
For photovoltaics, a class semiconductors favored is the one where there is no thermal wastage. The resolution is to then find the right material with the optimal band-gap with high collection efficiency. Semiconductors that fit in this class are called complex semiconductors. Complex semiconductors are inorganic in nature, which are made up of more than one element. Finding the right stoichiometry (proportion of the elements) of this complex poses a big challenge since it modulates the band-gap and it’s characteristic. End result is that the desired material has been achieved through years of trial and error, however the stoichoimetry is proprietary. In parallel, developing a technique to manufacture this material that is reliable over time has been a topic that is gaining a lot of attention with some recent success.
Recently, energy harvesting, an area where very low/ultra power is needed to harness power for device functionality such as sensors and actuators, has opened a new chapter in developing new solar cell materials and applications, namely tunable band-gap semiconductors. These are organic solar cells that are gaining a lot of attention for applications that abound across the light spectrum from IR to ultra-violet in the sensor market. Through this class of semiconductors, this area has morphed solar cells to become a key player in the consumer and industrial market, while the complex inorganic semiconductors, are being developed to achieve efficiencies at a manufacturing cost targeted to be equal to or better than grid parity for utility applications.
TI’s vision on low power devices such as energy harvesters and its expertise in both design and materials development could fuel this activity for the next technology frontier one of which is energy related.
Nagarajan Sridhar
