One-Step Lithography Nanostructured Au Encapsulation for Light Management in Ultrathin ACIGS Solar Cells

Abstract

Ultrathin (Ag,Cu)(In,Ga)Se₂ (ACIGS) solar cells enable material savings, high manufacturing throughput, and application versatility. Moreover, the reduced absorber thickness relieves European concerns about critical raw material shortages. However, ultrathin device performance does not yet compete with their thicker counterparts due to increased rear contact recombination and incomplete light absorption. This work proposes a rear contact architecture that encapsulates a 25 nm Au patterned layer with 20 nm of Al₂O₃, increasing the rear contact reflectance while passivating the rear interface defects. However, one of several challenges with nanofabrication is aligning two nanopatterns. Therefore, the nanofabrication of the rear architecture is optimized to encompass one-step nanoimprint lithography without requiring alignment. Two ACIGS absorber growth temperature values of 550 and 450 °C are evaluated, with attention to their effect on rear architecture integrity. The rear contact remains intact when the absorber growth temperature is 450 °C. In such conditions, the proposed architecture increases the solar cell conversion efficiency by 1.5% abs. compared to a reference cell with Mo, resulting from a short-circuit current density gain of 3.7 mA cm⁻². Therefore, this rear contact architecture may greatly benefit the performance of ultrathin solar cells deposited at low temperatures.