Over 16% efficiency organic photovoltaic cells enabled by a chlorinated acceptor with increased open-circuit voltages

Abstract

Broadening the optical absorption of organic photovoltaic (OPV) materials by enhancing the intramolecular push-pull effect is a general and effective method to improve the power conversion efficiencies of OPV cells. However, in terms of the electron acceptors, the most common molecular design strategy of halogenation usually results in down-shifted molecular energy levels, thereby leading to decreased open-circuit voltages in the devices. Herein, we report a chlorinated non-fullerene acceptor, which exhibits an extended optical absorption and meanwhile displays a higher voltage than its fluorinated counterpart in the devices. This unexpected phenomenon can be ascribed to the reduced non-radiative energy loss (0.206 eV). Due to the simultaneously improved short-circuit current density and open-circuit voltage, a high efficiency of 16.5% is achieved. This study demonstrates that finely tuning the OPV materials to reduce the bandgap-voltage offset has great potential for boosting the efficiency.

Watching Space Charge Build Up in an Organic Solar Cell

“…The efficiency of organic photovoltaics (OPVs) has increased from about 10% to over 16% within only a few years . The main driver of this rapid progress is the emergence of nonfullerene acceptors.…”

Barrierless Free Charge Generation in the High‐Performance PM6:Y6 Bulk Heterojunction Non‐Fullerene Solar Cell

“…Organic solar cells (OSCs) have gained renewed interest with the emergence of non‐fullerene acceptors (NFAs). Small molecule NFAs blended with donor polymers have rapidly advanced, reaching state‐of‐the‐art power conversion efficiencies above 16% for single junctions and 17.3% for all‐organic solution‐processed tandem cells . These NFA‐based blends benefit from a strong and redshifted absorption of the acceptor (A), complementary to the donor (D) absorption range, and small ionization energy offsets at the D/A heterojunction.…”

Accurate Determination of the Minimum HOMO Offset for Efficient Charge Generation using Organic Semiconducting Alloys

“…[4,5] For OSCs utilizing fullerene derivatives as electron acceptors, a lowest unoccupied molecular orbital (LUMO) offset [ΔE LUMO = E LUMO(D) − E LUMO(A) ] of no less than 0.30 eV was generally proposed to guarantee efficient electron transfer. [15][16][17][18][19][20][21] To form a complementary absorption, current popular NFA OSCs are based on the combination of a widebandgap donor and a narrow-bandgap acceptor. Thus far, the development of donor (D)-acceptor (A)-type nonfullerene molecular acceptors (NFAs) with well-tunable electronic structures has opened up a great opportunity in this active topic because these NFAs have realized high PCEs over 15%.…”