A Selenium‐Substituted Low‐Bandgap Polymer with Versatile Photovoltaic Applications

A reduction of the bandgap and an enhancement of the charge transport properties of a LBG polymer (PBDTT-DPP) can be achieved simultaneously by changing the sulfur atoms on the DPP unit to selenium atoms. The newly designed polymer, PBDTT-SeDPP (Eg = 1.38 eV), shows excellent photovoltaic performance in single junction devices with power conversion efficiencies (PCEs) over 7% and photo-response up to 900 nm. A tandem polymer solar cell and a visibly transparent solar cell based on PBDTT-SeDPP show 9.5% and 4.5% PCEs, which are superior to those based on PBDTT-DPP.