A tetracyclic-bislactone-based copolymer donor for efficient semitransparent organic photovoltaics

A copolymer donor PBDTTPTP based on a tetracyclic bislactone unit, thieno[2 & PRIME;,3 & PRIME;:5,6]pyrano[3,4-d]thieno[3,2-b]pyran-4,9-dione (TPTP), was developed. The single crystal structure of a TPTP derivative indicates the & pi;-extended planar geometry of TPTP and its good coplanarity with the adjacent thiophene units. Thanks to the strong electron-withdrawing properties and good coplanarity of TPTP, the copolymer PBDTTPTP shows a deep HOMO level of -5.60 eV, a small optical bandgap of 1.65 eV and a good hole mobility of 6.57 x 10(-4) cm(2) V-1 s(-1). These features make PBDTTPTP an efficient donor material for semitransparent organic photovoltaics (STOPVs). STOPVs based on PBDTTPTP and N3 gave a high light utilization efficiency of 4.38%, with a power conversion efficiency of 12.26% and an average visible light transmittance of 35.7%.