A novel stress design for the type-II hetero-junction solar cell with superior performance

Abstract

High efficient surface textured SiGe-based solar cell is proposed by the designed top nano-level surface trench structure and the optimized SiGe/Si type-II substrate hetero-junction design. The surface reflectance rate of solar cell can be successfully reduced about 3 times (totally from 32% to ∼10%) by the nano-surface textured structure with obvious photonic crystal effect, simulated by finite differential time domain simulation. With different top surface trench spacing (d) structure design on the nanometer level, broadband antireflection and total absorption rate can be realized and enhanced greatly, respectively. Moreover, SiGe/Si hetero-structure substrate is also implemented to enhance an additional solar cell efficiency about 3% in this work, not only due to the originally higher absorption rate in SiGe-based material but also due to optimized SiGe/Si type-II hetero-structure substrate design. The offset and discontinuousness of the energy band between n+-Si and grown fully strained Si0.9Ge0.1 type-II hetero-junction structure can prevent hole diffusion into the n+-Si layer and have the larger Voc. With the integration of these two key technologies including nano-level surface trench structure design and SiGe/Si type-II hetero-structure optimization, the high efficient (∼18% for the stable production and 21% for the peak record) nano-surface textured SiGe-based solar cell can be achieved and demonstrated in this work.