Ligand Engineering Enhances Fluorescence Properties of Eu‐Based Complexes for Efficiency Enhancement and UV Stability in Silicon Heterojunction Solar Cells

Abstract The development of silicon heterojunction (SHJ) solar cells is substantially constrained by two UV‐related limitations: insufficient photon utilization in UV spectrum and pronounced UV‐induced degradation. Downshifting luminescent materials address this by absorbing harmful UV photons and converting them into visible light that matches the spectral response range of SHJ solar cells. Herein, a high‐performance europium (Eu)‐based complex is demonstrated, Eu(TTA)₃Bath, synthesized using a π‐extended diphenyl‐conjugated ligand, achieving a record‐high quantum yield of 92.79%. Compared to Eu(TTA)₃Phen, the Eu(TTA)₃Bath complex exhibits superior and more stable luminescent properties due to optimized energy transfer. More importantly, the complex demonstrates excellent compatibility with polyvinyl butyral (PVB) matrix. To validate, Eu(TTA)₃Bath@PVB composite films are fabricated by blending the Eu(TTA)₃Bath complex with PVB powder and thermally cured on glass substrates, enhancing UV absorption while maintaining comparable visible transmittance. The optimized composite film demonstrates a 0.26%abs increase in the power conversion efficiency (PCE) when applied to SHJ solar cells, compared to the pristine PVB counterpart. Furthermore, it exhibits a 1.13%abs reduction in the PCE degradation under cumulative UV irradiation of 30 kWh m⁻² compared to the control group. The materials synthesized by this strategy offer potential to address efficiency limitations and UV instability in SHJ technology.