Determining the internal quantum efficiency of organic Bulk Heterojunctions based on mono and bis–adduct fullerenes as acceptor

With the aid of optical modeling, the internal quantum efficiencies of organic Bulk Heterojunction (oBHJ) photovoltaic devices based on low band gap polymer of 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) blended with the acceptors of 1-(3-Methoxycarbonyl) propyl-1-phenyl [6,6] C61 (PCBM) and bis–adduct (bis–PCBM) are determined. The Si-PCPDTBT:bis–PCBM devices show considerably lower short circuit current density (Jsc) as compared to the Si-PCPDTBT:PCBM devices. The results show that 30% of this smaller Jsc is due to the lower optical absorption of bis–PCBM, while the major losses originate from the electrical losses. It is found that for the best Si-PCPDTBT:bis–PCBM devices with an active layer thickness in the range of 70–100 nm, the inefficient charge generation within the bis–PCBM domains is the major contribution to the whole losses. Increasing the active layer thickness of Si-PCPDTBT:bis–PCBM device significantly enhances recombination losses in polymer/bis–fullerene matrix.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Organic solar cells based on mono and bis–adduct fullerenes were investigated. ► IQE of solar cells was determined using optical modeling and EQE measurements. ► Polymer/bis–PCBM devices suffer from low short circuit current density. ► Thin bis–fullerene devices show inefficient charge generation within the bis–PCBM domains. ► Charge recombination is enhanced for the thick bis-fullerene devices.