Excellent omnidirectional light trapping properties of inverted micro-pyramid structured silicon by copper catalyzed chemical etching

Nano/micro structuring of silicon (Si) attracts a lot of research interests for minimizing the reflective losses (>30%) of Si surface limiting the solar cell performance majorly. Here, arrays of inverted micro-pyramids Si (IP–Si) have been fabricated on large area of the solar-grade, as-cut Si wafers by a simple, one-step copper (Cu) catalyzed chemical etching (CuCCE) in aqueous etch bath of 5 mM-Cu(NO3)2/4.6M-HF/0.55M − H2O2 at 50 °C. Influence of etching time is investigated under constant etch bath parameters and starting surface properties of the Si wafers. The CuCCE mechanism is compared with the standard alkali (aq. KOH) texturing of Si(100) wafers. The formation of inverted structure is attributed to Cu nanoparticles catalyzed localized anisotropic as well as isotropic etching of Si(100) as compared to only anisotropic etching in the KOH texturing. The IP-Si surface offers a superior light trapping ability in broad spectral range compared to the conventional KOH based random upright micro-pyramids (UP–Si). The IP-Si surface could achieve solar weighted reflectance (SWR) as low as <7% in 400–1000 nm spectral range as compared to ∼14% of the UP-Si surfaces. This has been attributed to higher percentage of triple bounce interaction of the incident light with Si surface offered by the IP-Si. Further, the IP-Si offers enhanced omnidirectional light trapping for wide angle of incidence (AOI) of light (−40° to +40°) as compared to that in UP-Si. The enhanced omnidirectional light trapping of the IP-Si and its mechanism has further been explained by finite difference time domain (FDTD) simulation. Further, potential of IP-Si for enhanced solar cell performance is proposed on the basis of theoretical calculation of total photocurrent for planar, UP-Si and IP-Si surfaces. A simple, economic yet effective process for large area fabrication of the inverted micro/nano-pyramid arrays of Si with enhanced and broad band omnidirectional light trapping properties has been shown which has potential for efficient Si solar cell application.