Ultrafast Dynamics Group
Frédéric Laquai's Group

Negligible Energy Loss

Negligible Energy Loss During Charge Generation in Small-Molecule/Fullerene Bulk-Heterojunction Solar Cells Leads to Open-Circuit Voltage over 1.10 V

Negligible Energy Loss During Charge Generation in Small-Molecule/Fullerene Bulk-Heterojunction Solar Cells Leads 

to Open-Circuit Voltage over 1.10 V


M. Babics, T. Duan, A. H. Balawi, R.-Z. Liang, F. Cruciani, I.-D. Carja, D. Gottlieb, I. McCulloch, K. Vandewal, F. Laquai and P. M. Beaujuge ACS Appl. Energy Mater., 2019, DOI: 10.1021/acsaem.8b02020​

M. Babics, T. Duan, A. H. Balawi, R.-Z. Liang, F. Cruciani, I.-D. Carja, D. Gottlieb, I. McCulloch, K. Vandewal, F. Laquai and P. M. Beaujuge
organic photovoltaics, small-molecule donor, oligothiophene, fluorination, high open-circuit voltage, low energy loss
2019
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Solution-processable small molecules (SMs) that can serve as donors in bulk-heterojunction (BHJ) solar cells are practical alternatives to their polymer counterparts. However, SM–fullerene blends commonly suffer severe voltage losses. In general, devices that reach open-circuit voltages (VOC) > 1 V yield low photocurrents in BHJ solar cells with fullerene acceptors (e.g., PC71BM) and modest power conversion efficiencies (PCEs). In this contribution, we report on the design, synthesis, and BHJ device characteristics of a new SM donor, 2F-DRCN5T, yielding a VOC of up to 1.10 V with PC71BM as the fullerene acceptor, while maintaining PCEs > 7% (over 8% achieved upon solvent-vapor-annealing (SVA) treatment). The negligible energy loss during charge generation (ΔECT), the deep-lying HOMO of 2F-DRCN5T inferred from its large ionization potential (IP), the high charge-transfer-state energy (ECT) of the blend, and a reduced nonradiative voltage loss account for the high VOC achieved in BHJ solar cells.