Impact of Nanoscale Elemental Distribution in High-Performance Kesterite Solar Cells

The effort to develop earth-abundant kesterite solar cells has led to an approximate doubling of the power conversion efficiency over the past five years to 12.6%, primarily due to increases in short-circuit current and fill factor; open-circuit voltage has resisted similar change, limiting further efficiency improvement. In the present investigation, Auger nanoprobe spectroscopy, X-ray/ultraviolet photoelectron spectroscopy, and device characterization are used to provide a comprehensive understanding of the role of grain boundaries and interfaces in limiting performance in kesterite-based devices. High photovoltaic performance is found to correlate with grain boundaries that are Cu-depleted and enriched with SnOx. The formation of this bulk-like oxide at grain boundaries with type I band offset provides a unique effective passivation that limits electron-hole recombination. Building on these new insights, photovoltaic device simulations are performed that show optimized electrostatic designs can compensate for bulk defects, allowing efficiencies closer to the theoretical limit.