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

Abstract

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.