The present study aims at understanding the role of incorporating Cu _(2) S nanocrystals (NCs) as a third component in ternary organic solar cells. Ternary photoactive blends consisting of conjugated polymer poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2- b ;4,5- b ′]dithiophene-2,6-diyl- alt -(4-(2-ethylhexyl)-3-fluorothieno[3,4- b ]thiophene-)-(2-carboxylate-2-6-diyl)] (PTB7-Th), fullerene derivative phenyl-C _(71) -butyric acid methyl ester (PCBM) and different wt% of Cu _(2) S NCs were formulated and were employed to fabricate ternary OSCs having a device architecture of ITO/ZnO/PTB7-Th:Cu _(2) S NCs:PCBM/MoO _(3) /Ag. It has been observed that with the addition of 3 wt% of Cu _(2) S NCs, an improved power conversion efficiency (PCE) of 8.20% is obtained against the PCE of 6.96% for reference devices. EIS measurements and AFM studies suggests that the presence of Cu _(2) S NCs facilitates formation of cascading energy levels, provides smoother surfaces and helps in suppressing trap-assisted recombination.
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