A new non-fullerene acceptor, IDTBR, has been developed to enhance the performance of P3HT-based polymer solar cells. This acceptor, designed with an indacenodithiophene core and benzothiadiazole and rhodanine flanking groups, offers improved optoelectronic and morphological properties compared to previous acceptors like FBR. The IDTBR acceptor, when combined with P3HT, achieves a power conversion efficiency (PCE) of 6.4%, the highest reported for fullerene-free P3HT devices. This efficiency is attributed to the well-matched optoelectronic and morphological properties of the materials, which enable efficient charge separation and transport. Additionally, IDTBR demonstrates significantly improved air stability compared to other high-efficiency OPV, making it a promising candidate for future technological applications. The IDTBR acceptor was synthesized using a Stille coupling reaction followed by a Knoevenagel condensation. The acceptor's structure was optimized through side-chain engineering, with linear (n-octyl) alkyl chains yielding a more crystalline material with a further red-shifted absorption onset relative to branched (2-ethylhexyl) chains. This results in higher short-circuit current (Jsc) and PCE. The acceptor's planar structure enhances conjugation, which, when combined with the more electron-rich thiophene-based core, raises the highest occupied molecular orbital (HOMO). This leads to a significantly red-shifted UV-visible (UV-vis) absorption spectrum relative to that of FBR. The IDTBR acceptor also demonstrates improved charge-carrier mobilities and reduced recombination dynamics, contributing to higher fill factors (FF) and overall PCE. The acceptor's improved morphological stability, as evidenced by grazing incidence XRD (GIXRD) and differential scanning calorimetry (DSC) studies, allows for the formation of pure acceptor domains, which is crucial for efficient charge transport. The IDTBR acceptor's enhanced stability and performance make it a promising candidate for scalable and stable OPV devices. The study also highlights the potential of IDTBR in improving the efficiency and stability of OPV devices, particularly in ambient conditions.A new non-fullerene acceptor, IDTBR, has been developed to enhance the performance of P3HT-based polymer solar cells. This acceptor, designed with an indacenodithiophene core and benzothiadiazole and rhodanine flanking groups, offers improved optoelectronic and morphological properties compared to previous acceptors like FBR. The IDTBR acceptor, when combined with P3HT, achieves a power conversion efficiency (PCE) of 6.4%, the highest reported for fullerene-free P3HT devices. This efficiency is attributed to the well-matched optoelectronic and morphological properties of the materials, which enable efficient charge separation and transport. Additionally, IDTBR demonstrates significantly improved air stability compared to other high-efficiency OPV, making it a promising candidate for future technological applications. The IDTBR acceptor was synthesized using a Stille coupling reaction followed by a Knoevenagel condensation. The acceptor's structure was optimized through side-chain engineering, with linear (n-octyl) alkyl chains yielding a more crystalline material with a further red-shifted absorption onset relative to branched (2-ethylhexyl) chains. This results in higher short-circuit current (Jsc) and PCE. The acceptor's planar structure enhances conjugation, which, when combined with the more electron-rich thiophene-based core, raises the highest occupied molecular orbital (HOMO). This leads to a significantly red-shifted UV-visible (UV-vis) absorption spectrum relative to that of FBR. The IDTBR acceptor also demonstrates improved charge-carrier mobilities and reduced recombination dynamics, contributing to higher fill factors (FF) and overall PCE. The acceptor's improved morphological stability, as evidenced by grazing incidence XRD (GIXRD) and differential scanning calorimetry (DSC) studies, allows for the formation of pure acceptor domains, which is crucial for efficient charge transport. The IDTBR acceptor's enhanced stability and performance make it a promising candidate for scalable and stable OPV devices. The study also highlights the potential of IDTBR in improving the efficiency and stability of OPV devices, particularly in ambient conditions.