Platinum(II) polyyne polymers containing thiophene-acceptor-thiophene units are synthesized, and their main chain alkynes are functionalized by the formal cycloaddition–retro-electrocyclization reaction with tetracyanoethylene (TCNE). The polymer energy levels are significantly decreased by the TCNE addition. Bulk-heterojunction solar cells are fabricated using the TCNE-adducted platinum(II) polyyne polymers. The use of these polymers as p-type semiconductors in combination with n-type fullerene derivatives indicates that the p-type semiconducting ability decreases by approximately five to ten times after the TCNE addition. On the contrary, when the TCNE-adducted polymers are employed as a substitute for the fullerene derivatives, the all-polymer solar cells are initially fabricated.