Stepped metal gratings as an efficient way to design a broadband absorption efficiency and overcome recombination degradation in an organic solar cell

Abstract

The Stepped stopped Groove Metal nano-grating (SSGMG) and Stepped Through Groove Metal nano-grating (STGMG) with a stepped hole transport layer (HTL) and a coating layer, is investigated as a novel method to obtain high absorption efficiency in a thin film organic solar cell. Enhancement of the electric field inside the gratings due to the near field and far-field coupling of wedge plasmon polaritons would lead to the improvement of the absorption efficiency of the solar cell. The proposed SSGMG model, with a 40 nm thickness of the photoactive layer, shows an absorption efficiency of 73.73% of the incident light in a wavelength range from 350 nm to 800 nm. the results show that the SSGMG model with an effective thickness of 40 nm has improved the absorption efficiency of the thickness-equivalent planar model (without coating layer) up to 133% of its initial value. Moreover, the effect of the incident angle (θ) and polarization angle (α) on the absorption efficiency was evaluated. We have found that SSGMG would lead to better absorption efficiency than STGMG because of its advantages over unpolarized light absorption. Excitation of surface plasmon polaritons inside the photo-active layer would help to reduce the recombination degradation as a result of the reduced thickness of the active layer as well as the enhanced mobility of charge. The designed structures can be used to overcome recombination degradation which is the intrinsic limitation of organic materials.