High Efficiency (>10%) AgBiS₂ Colloidal Nanocrystal Solar Cells with Diketopyrrolopyrrole-Based Polymer Hole Transport Layer

Silver bismuth disulfide (AgBiS₂) colloidal nanocrystals (CNCs) have emerged as ecofriendly photoactive materials with excellent photoconductivity and high absorption coefficients, in compliance with the restriction of hazardous substances (RoHS) guidelines. To maximize the theoretical potential of AgBiS₂ CNC solar cells, a new diketopyrrolopyrrole (DPP)-based polymer, BD2FCT, optimized as a hole transport layer (HTL), is developed. This asymmetric thiophene-rich polymer HTL effectively complements the optical absorption spectrum of CNCs and forms a homogeneous layer atop the CNCs, facilitating favorable vertical charge transfer through intrinsic molecular packing. Furthermore, the BD2FCT HTL aligns energetically with AgBiS₂, significantly reducing charge recombination at the CNC/HTL interfaces and enhancing charge extraction and photocurrent generation across the entire optical absorption spectrum. These characteristics are further optimized through precise molecular engineering. Additionally, a low-bandgap acceptor, IEICO-4F, is structurally incorporated with the BD2FCT polymer to further improve charge funneling and complementary absorption. Transient absorption spectroscopy reveals enhanced hole transfer from CNC to BD2FCT-29DPP:IEICO-4F, resulting in reduced charge recombination and efficient charge extraction. Consequently, a BD2FCT-based AgBiS₂ CNC solar cell achieves a power conversion efficiency (PCE) of 10.1%, demonstrating significant improvements in short-circuit current density (J_SC) and fill factor (FF).