Surface Passivation of Nanostructured Silicon Surfaces to Reduce Optical and Recombination Losses

Project Support

• U.S. Department of Energy Office of Science User Facility
• Brookhaven National Laboratory for Functional Nanomaterials
• Dates: 2019-2021

Key Investigators and Collaborators

• Kristopher O. Davis - Principal Investigator, DPV Group Leader
• M Jobayer Hossain - Graduate Student in DPV Group, now Assistant Professor at the University of North Dakota
• Gregory Doerk - Brookhaven National Laboratory

The Challenge

While dielectric nanostructures effectively enhance optical absorption in semiconductors by trapping light and reducing front-surface reflection, surfaces often introduce competing losses. A major culprit is charge carrier recombination due to surface defect states. Our research aims to address both optical and electrical losses simultaneously.

Our Approach

In collaboration with Brookhaven National Laboratory, we demonstrated that strategically designed nanomaterials can serve a dual purpose: photon management and surface passivation. Utilizing directed self-assembly, we engineered ordered arrays of aluminum oxide (Al₂O₃) nanostructures in various tunable geometries, including lamellae, nanoholes, and nanopillars.

Scanning electron microscopy (SEM) images of aluminum oxide nanostructures formed on silicon wafers via directed self-assembly.

Findings

We validated this multifunctional capability experimentally through injection-level dependent photoconductance measurements and reflectance spectroscopy. Complementary finite element simulations on technologically relevant rear contact architectures confirmed that thicker nanostructures with larger coverage areas maximize rear internal reflectance.

Our models predict significant performance boosts for silicon photovoltaic (PV) cells:

• ≈0.9–1.0 mA/cm² increase in short-circuit current density for aluminum rear contacts (on 170 μm and 50 μm thick absorbers, respectively).
• 2.1–2.9 mA/cm² increase for Ni–Cu rear contacts.