We replace the side-chains from tri(n-propyl)silylthienyl to tri(n-propyl)silylethynyl and report two alkynyl-decorated 2D conjugated narrow-bandgap (~1.4 eV) nonfullerene acceptors, named ISI-4F and ISI-4Cl. The two 2D conjugated nonfullerene acceptors featured the conjugation of π-electrons of ethynyl side-chain and backbone, leading to enhanced absorptivity and downshifted energy levels, and showed around 16% efficiencies when employed as acceptor guests of PM6:Y6.