The optical performance of random and periodic textured mono crystalline silicon surfaces for photovoltaic applications

Abstract

Surface textures that result in high optical yields are crucial for high efficiency photovoltaic (PV) devices. In this work three different texturing approaches are presented that result in smooth concave structures devoid of sharp features. Such features can sustain the crack-free growth of device quality nano- to poly-crystalline materials such as nano-crystalline silicon, perovskites or C(I)GS, facilitating routes towards hybrid multijunction PV devices. A sacrificial implanted poly-c-Si layer is used to develop a random surface texture for the first texturing approach (Tsac). The influence of the processing conditions, such as layer thickness, implantation energy, dose and ion type, annealing time and temperature, of the sacrificial layer on the developed surface features is investigated. Additionally, a photolithographically developed honeycomb texture (Thoney) is presented. The influence of mask design on the honeycomb features is discussed and a relation is established between the honeycomb period and crack formation in nano-crystalline silicon layers. The reflective properties (spectral reflection, haze in reflection and angular intensity distribution) of these approaches are characterized and compared to a third texturing approach, Tsp, the result of chemically smoothened pyramidal <111> features. It was demonstrated that high optical scattering yields can be achieved for both Thoney and Tsp. Additionally, the performance of a-Si/nc-Si tandem devices processed onto the different textures is compared using both optical device simulations and real device measurements. Simulations demonstrate strong improvements in Jsc-sum (≈45%), in reference to a flat surface, and high Voc*FF of over 1 V are demonstrated for Tsp.