Ultra-Efficient Flexible Silicon Solar Cell Technology

Motivation Energy transition from fossil fuels to renewables is underway, with renewables comprising ~9% (7% hydro, 2% other) of the global energy consumption. Researchers’ have reported on the potential of renewables to markedly if not completely replace fossil fuels by 2050 through wind, water and sunlight based energy generation for the 50 United States. These and other studies suggest that the benefits of complete electrification are far-reaching in that it: helps mitigate climate change, eliminates air pollution mortality, creates jobs, and reduces power demand by ~40%, principally due to far better electrical energy to work conversion efficiencies over combustion processes.

Transitioning the energy infrastructure to renewables can be met by ~50% wind (~30% on-shore and ~20% off-shore) and ~40% photovoltaics (~30% utility and ~10% roof-top). Crystalline silicon photovoltaics (PV), with demonstrated efficiency exceeding 26%, has and continues to dominate the global PV market share at greater than 90%. While photovoltaics is poised to provide the lowest cost electricity, it does require further reduction in costs (cell, module and installation) to propel the above transition. Moreover, a further increase in photovoltaic conversion efficiency would directly drive down these costs and hence the levelized cost of electricity.

Motivated by the vision of a renewably powered world, this project aims to further advance silicon photovoltaic technology whereby economic flexible silicon solar cells become ubiquitous.

Science and Technology Since the first demonstration of 6% efficient diffused silicon solar cell at Bell Labs in 1954, enormous scientific and technological strides have been made culminating in greater than 26% photovoltaic conversion efficiency for single junction crystalline silicon – this happened in 2016, some 62 years after the first demonstration. Concurrently, and in particular over the last decade, the total installation capacity has increased 40-fold with module prices dropping from US$4 per watt to less than US$0.40 per watt. These achievements are clearly a function of sustained steadfast research and development of a range of technology elements that include improvements in the electronic quality of the silicon absorber, enhancement of passivation quality of device surfaces, implementation of front and rear surface fields, minimization of contact and series resistances, and optimization of optical absorption.

Scientifically, the common view today is that silicon photovoltaics has largely reached its maximal conversion efficiency and that silicon wafer thickness may drop a little but will hover for the most part in the150 micron to 100 micron range. Hence, the prevailing outlook is to drive photovoltaic conversion efficiencies toward 30%-plus by integrating silicon with various novel solar cell material technologies (such as perovskites, quantum dots, organics) and thus create dual/multi-junction silicon based solar cells.

However, a new emerging view on silicon is that there is still potential for making further gains. In particular, silicon can be thinned substantially and through integration of novel photonic structuring and device constructs it is deemed possible to achieve and exceed state-of-the-art silicon photovoltaic conversion efficiency.

The successful realization of this new silicon paradigm can potentially result in disruptive implications in the renewable energy space which are:

· Driving silicon to new performance levels – toward photovoltaic conversion efficiency of 29% on ultra-thin silicon;

· Advancing silicon economically toward 1 cent US per kWh; and

· Re-inventing silicon by making it flexible and ultra-efficient, and thus rendering it truly ubiquitous (for example, applications that would include building integrated PV, automotive/transportation integrated PV, consumer/electronic product integrated PV).