A low band-gap poly-yne, Poly[1,4-dioctyloxyphenylene-2,5-diylethynylene-2,3-diphenylthieno[3,4-b]pyrazine-5,7-diyl)ethynylene] (P) comprising of alternative units of 2,3-diethynyl-5,7-diphenylthieno[3,4-b]pyrazine and 2,5-dioctyloxyphenylene has been synthesized and characterized. The p-type poly-yne P was then mechanically blended with n-type acceptor material N,N'-bis(1-ethylpropyl)-3,4:9,10-perylene bis(tetracarboxyldiimide) (PTCDI) for solar cell (SC) studies. A series of SCs were fabricated with varying blend ratio of P and PTCDI, and their SC performance has been evaluated. Effect of thermal annealing on a blend of P and PTCDI has also been tested. A fullerene-free SC with external quantum efficiency (EQE) of 5.5% has been achieved successfully for the blend of 10 P: 90 PTCDI. The structures of P and PTCDI have been optimized, and their HOMO and LUMO energy levels have been determined by the DFT calculation to complement the observed SC performance of the materials. The poly(platina-ynes) (M1) incorporating 2-amino-1,4-phenylene spacer has been synthesized, and this p-type donor material M1 was then covalently linked to an n-type acceptor material, 4-fluoro-3,5-dinitrobenzoyl-o-quinodimethane[60] fullerene derivative (C60-DNF) to synthesize M2, where both D and A are present within the same material. The SC performance of the device made of M2 has been evaluated. In addition, SC performance of a mechanical blend of M1 and M2 with another fullerene derivative, C60-Me have been evaluated separately. To understand the energy transfer efficiency in SC performance of these materials, model dimeric complexes M3 and M4 were designed, and their structures have been optimized, and HOMO and LUMO energy levels have been determined by DFT calculation, which was then compared with M1 and M2. New acetylide-functionalized non-fused and fused heteroarylethynylpyridine-based ligands (L = L1-L6) incorporated CuI clusters (C1-C6) have been synthesized via coordination driven self-assembly of CuI, L, and PPh3 (R1) in dichloromethane and completely characterized. The rhomboid dimeric structure (for C1, C2, C4, and C5) and polymeric structure (for C6) have been determined by single crystal X-ray crystallography. A series of related CuI clusters (C7-C13) bearing carboxylic acid (R2)/sulfonic acid anchored PPh3 (R3) have also been synthesized and employed as sensitizers for the DSSC application. Complexes C7-C13 displayed a moderate PCE in the range of 0.07% to 1.56%, and the highest performance has been obtained for C13 bearing ethynylterthienylpyridnyl ligand and PPh3-SO3H co-ligand. The structures of all complexes have been optimized, and their HOMO and LUMO energy levels have been determined by DFT calculation to complement the observed SC performance.