Fabrication of silver sulfide thin films for efficient organic solar cells with high short-circuit currents based on double heterojunctions

Efficient solar cells based on Ag2S/P3HT and PCBM/P3HT heterojunctions are fabricated, in which the Ag2S nanoparticles are deposited on ITO glass via a newly developed high-speed rotating thermal decomposition method as an electron selective layer and a light absorption material. The ITO/Ag2S(n)/P3HT:PCBM films have a complementary effect in the light absorption due to the narrow band gap of Ag2S. The Ag2S nanoparticles in the upper layer of Ag2S film form a vertical nanotree-structure after many cycles of Ag2S deposition and lead to the formation of Ag2S/P3HT bulk heterojunction, which facilitates exciton dissociation at the P3HT/Ag2S interfaces and made Ag2S nanocrystals electron-transport materials in the active layers. Moreover, the Ag2S make a contribution to the photocurrent as a light absorber. The maximum power conversion efficiency of 3.21% is achieved for the fabricated ITO/Ag2S(50)/P3HT:PCBM/MoO3/Au solar cell with high short-circuit current, which is 1.13 times the best efficiency (2.84%) of the ITO/dense-TiO2/P3HT:PCBM/MoO3/Au cell made by the high-temperature process and is also much higher than that of reported similar hybrid solar cells based on Ag2S/conjugated polymer heterojunction. The improvement of the efficiency may result from the reduced charge recombination and increased light absorption due to the formation of Ag2S. (C) 2015 Elsevier B.V. All rights reserved.