This work describes the utilization of D-A-D type organic semiconductor, 4,4’-(benzo[c] [1,2,5]selenadiazole-4,7-diyl)bis(N,N-diphenylaniline), denoted as Se-2TPA, containing benzoselenadiazole (BSe) as acceptor core and end-capped with triphenylamine (TPA) donor units as donor materials in solar cells. Superlatively, the attachment of TPA donor moiety in BSe acceptor unit enlarged the conjugated system by extending the π-bonding which effectively tuned the optical and electrochemical properties of Se-2TPA. The bulk heterojunction organic solar cell (BHJ-OSCs) with configuration of ITO/cp-TiO2/Se-2TPA:PC61BM/Au showed power conversion efficiency (PCE) of ∼4.12% with short circuit current (Jsc) value of ∼11.28 mA/cm2, open circuit voltage (Voc) of ∼0.775 V and fill factor (FF) of ∼0.48. PCE significantly increased from ∼4.12% to ∼5.29% when 1,8-diiodooctane (DIO) was added as an additive in Se-2TPA:PC61BM blend which associated with less phase separation and improved the charge extraction. The fabricated BHJ-OSCs processed with 3% DIO, ITO/cp-TiO2/Se-2TPA:PC61BM/Au configuration displayed a long-term stability under air condition at an ambient temperature by maintaining ∼80% PCE for the duration of 30 days. The advantages of easy synthesis, low cost and promising cell performance supported Se-2TPA as successful organic semiconductor for BHJ-OSCs.