Speaker
Description
Transparent p–n junctions are essential for the next advancement in transparent electronics (displays, sensors, or solar cells). The challenges arise from the lack of high-quality p-type transparent conducting oxides. A promising candidate is CuCrO2, a wide-bandgap delafossite, which offers both p-type conductivity and strong transparency.
In this P4F project, pulsed laser deposition (PLD) was employed to systematically optimize p-type CuCrO₂ thin films. Using the third harmonic of a pulsed nanosecond Nd:YAG laser for target ablation, key deposition parameters, including oxygen partial pressure, substrate temperature and Cu/Cr ratio, were optimized. The optimized film, deposited at 700 °C and 2.3 mPa O₂, exhibited 64% average visible transmittance and an electrical conductivity of 62.5 S cm-1. These values correspond to a record Gordon figure of merit of 6150 µS and a Haacke figure of merit of 1.2 × 10-5 S, demonstrating substantial progress toward high-performance p-type transparent conducting films. XPS analysis revealed a high Cu/Cr ratio in the optimized film, suggesting Cu antisite defects as the origin of the enhanced conductivity.
Alternatively, to control the Cu concentration in the coatings, two KrF excimer laser beams simultaneously ablated CuO and Cr2O3 ceramics. This strategy enabled single-step deposition of films with Cu/Cr ratios from 0.6 to 1.4 across Cu-poor and Cu-rich regimes, without requiring separate targets for each composition. Structural and optoelectronic analyses showed polycrystalline, multiphase films containing CuCrO2, Cu2O, Cr2O3, Cu, and Cr, with CuCrO2 as the dominant phase. The films retained approximately 60% visible transparency and an optical bandgap of about 3.2 eV. Notably, the Cu-deficient film with Cu/Cr = 0.6 exhibited improved conductivity and a higher figure of merit, among synthesized samples, confirming Cu deficiency as an effective route to enhance conductivity while maintaining transparency.
Current efforts focus on fabricating high-performance plasmonic p-Cu1+xCr1-xO₂/n-AZO transparent p–n junctions. Based on the progress achieved, the project is on track to meet its planned milestones by the end of this year. Overall, this work establishes a clear pathway for developing high-performance p-type CuCrO2-based TCOs and integrating them into transparent p–n junctions for energy-efficient next-generation transparent electronics.