Semitransparent PbS/BiFeO ₃ Composite Photovoltaics With Selective UV–NIR Absorption Enabled by Size‐Modulated Quantum Dots

To address the dual requirements of high efficiency and high transparency for building‐integrated photovoltaics (BIPV), this study designed and fabricated a composite thin film with selective ultraviolet–near‐infrared (UV–NIR) absorption, based on a calcium/chromium‐codoped bismuth ferrite (BCFCO) ferroelectric layer and lead sulfide (PbS) quantum dots (QDs). Using a spin‐coating‐assisted successive ionic layer adsorption and reaction (SILAR) method, PbS QDs of different sizes (12, 14, and 16 nm) were grown in situ on TiO 2 /BCFCO substrates. The influence of QD size on the semitransparent photovoltaic properties and carrier behavior of the composite film was systematically investigated. The results show that increasing the QD size reduces the bandgap and enhances near‐infrared absorption, thereby improving the short‐circuit current density ( J sc ) and power conversion efficiency (PCE). However, this comes at the cost of reduced average visible transmittance (AVT). Ultimately, the device with 14 nm PbS QDs achieved excellent performance with a PCE of 4.63% and an AVT of 24.31%, yielding a high light utilization efficiency (LUE) of 112.56% 00 . These results demonstrate that precise size control of PbS QDs enables an optimal balance between photovoltaic performance and optical transparency, validating the effectiveness of the PbS QD integration approach for semitransparent applications.