The
correlated donor/acceptor (D/A) molecular orientation plays a crucial
role in solution-processed all-polymer solar cells in term of photovoltaic
performance. For the conjugated polymers PTB7-th and P(NDI2OD-T2),
the preferential molecular orientation of neat PTB7-th films kept
face-on regardless of the properties of processing solvents. However,
an increasing content of face-on molecular orientation in the neat
P(NDI2OD-T2) films could be found by changing processing solvents
from chloronaphthalene (CN) and <i>o</i>-dichlorobenzene
(oDCB) to chlorobenzene (CB). Besides, the neat P(NDI2OD-T2) films
also exhibited a transformation of preferential molecular orientation
from face-on to edge-on when extending film drying time by casting
in the same solution. Consequently, a distribution diagram of molecular
orientation for P(NDI2OD-T2) films was depicted and the same trend
could be observed for the PTB7-th/P(NDI2OD-T2) blend films. By manufacture
of photovoltaic devices with blend films, the relationship between
the correlated D/A molecular orientation and device performance was
established. The short-circuit current (<i>J</i><sub>sc</sub>) of devices processed by CN, oDCB, and CB enhanced gradually from
1.24 to 8.86 mA/cm<sup>2</sup> with the correlated D/A molecular orientation
changing from face-on/edge-on to face-on/face-on, which could be attributed
to facile exciton dissociation at D/A interface with the same molecular
orientation. Therefore, the power conversion efficiency (PCE) of devices
processed by CN, oDCB, and CB improved from 0.53% to 3.52% ultimately
