Toward High‐Temperature Stability of PTB7‐Based Bulk Heterojunction Solar Cells: Impact of Fullerene Size and Solvent Additive. Issue 4 (7th November 2016)

• Record Type: Journal Article
• Authors: Dkhil, Sadok Ben; Pfannmöller, Martin; Saba, Maria Ilenia; Gaceur, Meriem; Heidari, Hamed; Videlot‐Ackermann, Christine; Margeat, Olivier; Guerrero, Antonio; Bisquert, Juan; Garcia‐Belmonte, Germa; Mattoni, Alessandro; Bals, Sara; Ackermann, Jörg
• Is Part Of: Advanced energy materials. Volume 7:Issue 4(2017)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2016-11-07
• Subjects: additive -- bulk heterojunction -- polymer solar cells -- PTB7 -- stability; Energy harvesting -- Materials -- Periodicals; Energy conversion -- Materials -- Periodicals; Energy storage -- Materials -- Periodicals; Photovoltaics -- Periodicals; Fuel cells -- Periodicals; Thermoelectric materials -- Periodicals; 621.31
• DOI: 10.1002/aenm.201601486
• Languages: English
• ISSNs: 1614-6832

Abstract

Abstract : The use of fullerene as acceptor limits the thermal stability of organic solar cells at high temperatures as their diffusion inside the donor leads to phase separation via Ostwald ripening. Here it is reported that fullerene diffusion is fully suppressed at temperatures up to 140 °C in bulk heterojunctions based on the benzodithiophene‐based polymer (the poly[[4, 8‐bis[(2‐ethylhexyl)oxy]‐benzo[1, 2‐b:4, 5‐b′]dithiophene‐2, 6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]‐thieno[3, 4‐b]thiophenediyl]], (PTB7) in combination with the fullerene derivative [6, 6]‐phenyl‐C71‐butyric acid methyl ester (PC70 BM). The blend stability is found independently of the presence of diiodooctane (DIO) used to optimize nanostructuration and in contrast to PTB7 blends using the smaller fullerene derivative PC70 BM. The unprecedented thermal stability of PTB7:PC70 BM layers is addressed to local minima in the mixing enthalpy of the blend forming stable phases that inhibit fullerene diffusion. Importantly, although the nanoscale morphology of DIO processed blends is thermally stable, corresponding devices show strong performance losses under thermal stress. Only by the use of a high temperature annealing step removing residual DIO from the device, remarkably stable high efficiency solar cells with performance losses less than 10% after a continuous annealing at 140 °C over 3 days are obtained. These results pave the way toward high temperature stable polymer solar cells using fullerene acceptors. Abstract : Thermal stability of poly[[4, 8‐bis[(2‐ethylhexyl)oxy]benzo[1, 2‐b:4, 5‐b′]dithiophene‐2, 6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)‐carbonyl]thieno[3, 4‐b]thiophenediyl]]‐based solar cells is found to depend on fullerene size and solvent additive. While [6, 6]‐phenyl‐C71‐butyric acid methyl ester diffusion is suppressed inside blends independently of the solvent additive, only removing residual additive by 140 °C annealing leads to solar cells resisting 140 °C over days with performance losses less than 10%.