Parallel bulk heterojunction photovoltaics based on all-conjugated block copolymer additivesElectronic supplementary information (ESI) available: Experimental details, average values for device characteristics, 1H NMR spectra of polymers, TEM images of ternary blends, and GIWAXS data for ternary blends. See DOI: 10.1039/c6ta06502c

• Main Authors: Mok, Jorge W, Kipp, Dylan, Hasbun, Luis R, Dolocan, Andrei, Strzalka, Joseph, Ganesan, Venkat, Verduzco, Rafael
• Format: Journal Article
• Published: 27.09.2016
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c6ta06502c

In recent studies, we demonstrated that the addition of block copolymers to binary donor-acceptor blends represents an effective approach to target equilibrium, co-continuous morphologies of interpenetrating donors and acceptors. Here, we report a study of the impact of all-conjugated poly(thieno[3,4- b ]-thiophene- co -benzodithiophene)- b -polynaphthalene diimide (PTB7- b -PNDI) block copolymer additives on the electronic properties and photovoltaic performance of bulk heterojunction organic photovoltaic active layers comprised of a PTB7 donor and a phenyl-C 61 -butyric acid methyl ester (PCBM 61 ) acceptor. We find that small amounts of BCP additives lead to improved performance due to a large increase in the device open-circuit voltage ( V OC ), and the V OC is pinned to this higher value for higher BCP additive loadings. Such results contrast prior studies of ternary blend OPVs where either a continuous change in V OC or a value of V OC pinned to the lowest value is observed. We hypothesize and provide evidence in the form of device and morphology analyses that the impact of V OC is likely due to the formation of a parallel bulk heterojunction made up of isolated PCBM and PNDI acceptor domains separated by intermediate PTB7 donor domains. Altogether, this work demonstrates that all-conjugated block copolymers can be utilized as additives to both dictate morphology and modulate the electronic properties of the active layer. All-conjugated block copolymer additives enhance open circuit voltage through formation of parallel-type bulk heterojunction photovoltaics.