Optical absorption driven by efficient refraction and light concentration for photovoltaic applications

Broadband absorption of the solar spectrum is a prerequisite to any photovoltaic technology. Subwavelength arrays are known to provide various mechanisms for broadband and omnidirectional absorption of the solar spectrum. In the current work we examine optical absorption in NP arrays decorated with SiO2 quasi-nanolenses (qNL arrays), which numerically exhibit 10-15 % increase in broadband absorption. Specifically, near-field scanning optical microscopy (NSOM) is employed to probe the underlying optical absorption mechanisms. Two NSOM methods are employed for the investigation: 1) far-field imaging using near-field excitation which allows the determination as to the origin of the reflected far-field photons, and 2) far-field excitation and nearfield scanning to measure the lateral optical propagations in the arrays. We show that the enhanced optical absorption in qNL arrays is due to combination of three mechanisms: 1) each qNL serves as an effective antireflection coating, 2) the presence of qNLs increases the optical interactions between the adjacent dielectrics to conclude elevated levels of light trapping, and 3) the presence of qNL induces strong light concentration of the incoming radiation into the dielectric structures.

Automated summary

This study found that decorating subwavelength arrays with SiO2 quasi-nanolenses (qNL arrays) can enhance the absorption of the solar spectrum. Optical absorption mechanisms in qNL arrays were investigated using near-field scanning optical microscopy (NSOM), revealing that the enhancement is a result of the combination of effective antireflection coating, increased optical interactions between adjacent dielectrics for elevated light trapping, and strong light concentration due to the presence of qNLs.