2-Alkyl(1)alkyl(2)-type aliphatic side chains with a branching point position at the C2-position (such as 2-ethylhexyl or 2-octayldodecyl) have been widely implanted into numerous donor-acceptor conjugated copolymers for solution processable transistors or organic solar cells. However, the tertiary branching site located at the second carbon inevitably imposes steric hindrance that twists the main-chain coplanarity and attenuates interchain interactions. In this research, we developed a new two-dimensonal thiophene-vinylene-thiophene (TVT) derivative where a carbon-carbon triple bond is inserted between the thiophene unit and the 2-octyldodecyl group. This acetylene-incorporated TVT (aTVT) was copolymerized with 5,10-di(thiophen-2-yl)naphtho[1,2-c:5,6-c′]bis([1,2,5]thiadiazole) (DTNT) and 5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (DTFBT) to form the polymers PaTVT-NT and PaTVT-FBT, respectively. PTVT-FBT, without the triple bond, was also prepared for comparison. The insertion of a linear triple bond moves the tertiary carbon away from the main chain to reduce the steric hindrance, thereby improving the main-chain coplanarity and facilitating the interchain interactions. The acetylene-incorporated copolymers show better thermal stability, red-shifted absorption spectra, stronger intermolecular aggregation, lower-lying electron affinity, and much higher solid-state crystallinity. Due to the linear and coplanar polymeric backbone supported by theoretical calculation, PaTVT-NT exhibits high crystallinity and adopts strong stacking with an edge-on orientation in the thin film evidenced by 2D-GIXRD, leading to a high p-type OFET mobility up to 1.27 cm2 V-1 s-1 with an on-off ratio of 9.22 × 105. This value represents the highest value among the NT-based polymers. PaTVT-FBT also achieved a high mobility of 0.78 cm2 V-1 s-1, which greatly outperforms the corresponding nonacetylene PTVT-FBT counterpart. Most importantly, the preparation of 2-alkyl(1)alkyl(2)-acetylenyl side chain is synthetically feasible, which can be easily applied to create new conjugated polymers for high-performance solution-processable optoelectronics.