Medium Bandgap Nonfullerene Acceptor for Efficient Ternary Polymer Solar Cells with High Open-Circuit Voltage

Abstract

We have designed a new medium bandgap non-fullerene small-molecule acceptor consisting of an IDT donor core flanked with 2-(6-oxo-5,6-dihydro-4H-cyclopenta[c]-thiophene-4-ylidene) malononitrile (TC) acceptor terminal groups (IDT-TC) and compared its optical and electrochemical properties with the IDT-IC acceptor. IDT-TC showed an absorption profile from 300 to 760 nm, and it has an optical bandgap of 1.65 eV and HOMO and LUMO energy levels of −5.55 and −3.83 eV, respectively. In contrast to IDT-IC, IDT-TC has an upshifted LUMO energy level, which is advantageous for achieving high open-circuit voltage. Moreover, IDT-TC showed higher crystallinity and high electron mobility than IDT-IC. Using a wide bandgap D–A copolymer P as the donor, we compared the photovoltaic performance of IDT-TC, IDT-IC, and IDT-IC-Cl nonfullerene acceptors (NFAs). Polymer solar cells (PSCs) using P: IDT-TC, P: IDT-IC, and P:IDT-IC-Cl active layers achieved a power conversion efficiency (PCE) of 14.26, 11.56, and 13.34%, respectively. As the absorption profiles of IDT-IC-Cl and IDT-TC are complementary to each other, we have incorporated IDT-TC as the guest acceptor in the P: IDT-IC-Cl active layer to fabricate the ternary (P:IDT-TC: IDT-IC-Cl) PSC, demonstrating a PCE of 16.44%, which is significantly higher than that of the binary BHJ devices. The improvement in PCE for ternary PSCs is attributed to the efficient exploitation of excitons via energy transfer from IDT-TC to IDT-IC-Cl, suitable nanoscale phase separation, compact stacking distance, and more evenly distributed charge transport.

Small molecular donor materials based on β–β-bridged BODIPY dimers with a triphenylamine or carbazole unit for efficient organic solar cells

“…Their optical, thermal, and electrochemical properties were investigated. We have used these BODIPY-based small molecules as the donor and fullerene derivatives (PC 71 BM) and non-fullerene small molecule acceptor (IDT-TC) 43 as the acceptor for the fabrication of all small molecule OSCs. A comparison with the PCEs of BHJ solar cells based on reported BODIPY compounds is given in Table 1.…”