Enhanced performance of layer-evolved bulk-heterojunction solar cells with Ag nanoparticles by sequential deposition

Organic photovoltaic devices based on layer-evolved bulk-heterojunction (LE-BHJ) from poly{[4,4′-bis(2-ethylhexyl) dithieno(3,2-b:2′,3′-d)silole]-2,6-diyl-alt-[4,7-bis(2-thienyl)-2,1,3-benzothiadiazole]-5,5′-diyl} (Si-PCPDTBT)/[6,6]-phenyl C₇₁ butyric acid methyl ester (PC₇₁BM) are successfully fabricated by a sequential solution deposition process. During the process of a top layer being deposited from an appropriate cosolvent ratio control, the top layer of PC₇₁BM vertically penetrates a pre-coated layer of Si-PCPDTBT, resulting in an inter-diffused nanostructure with an LE-BHJ surface morphology. The LE-BHJ cells exhibit improved nanoscale phase separation and comparable performance, in comparison with the conventional BHJ device. Furthermore, Ag nanoparticles (NPs) with optimized ratio embedded LE-BHJ exhibit significant enhanced efficiency in comparison with the conventional BHJ and pristine LE-BHJ devices, because the multiple scattering from the Ag NPs leads to longer optical paths, which give rise to effective absorptivity and reduced leakage current within the BHJ active film.