Compared with other all-inorganic/organic–inorganic
hybrid
solar cells, the large voltage loss (V
loss) of organic photovoltaic (OPV) cells, especially the nonradiative
voltage loss (ΔV
nonrad), limited
the further improvement of performance. Although A-DA′D-A-type
Y-series nonfullerene acceptors (NFAs) largely improve the power conversion
efficiencies (PCEs) to 18%, the open-circuit voltage (V
OC) of this kind of material was still restricted to below
1.0 V. Herein, we designed and synthesized a narrow bandgap (E
g = 1.41 eV) acceptor BTA77 with
an A-DA′D-A-type backbone containing a nonhalogenated terminal
group to achieve high electroluminescence efficiency and high V
OC. Combined with the nonhalogenated polymer PBDB-T with a conjugated thiophene side chain, BTA77 realized a V
OC of 0.944 V, a V
loss of 0.552 V, and a PCE of 13.75%, which
is one of the highest PCEs based on nonhalogenated A-DA′D-A-type
acceptors with V
OC > 0.9 V. After further
blending with the nonhalogenated donor polymer PBT1-C with a conjugated phenyl side chain, the V
OC increases to 1.021 V with a super low ΔV
nonrad of 0.14 V owing to the greatly improved electroluminescence
external quantum efficiency (EQEEL) of 4.42 × 10–3. Our results indicate that there is still a large
room to decrease the ΔV
nonrad and
increase V
OC by synergistic molecular
engineering of p-type polymers and n-type small molecules.