Using lateral bulk heterojunctions to study the effects of additives on PTB7:PC61BM space charge regions

• A method for directly probing the active layer of photovoltaic devices.
• Visualization of the spatial extent of space charge regions within the device.
• Visualization of the spatial extent of the recombination zone.
• Effects of the additive DIO on these regions in PTB7 under working conditions.

Lateral bulk heterojunctions (LBHJ) provide a tool to directly probe the active area of photovoltaic devices using microscopy techniques. Here, we use scanning photocurrent microscopy (SPCM) to probe an organic photovoltaic (OPV) device with 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):[6,6]phenyl-C61-butyric acid methyl ester (PC61BM). The effects of the additive 1,8-diiodooctane (DIO) on the recombination dynamics and morphology are probed in real space in a LBHJ structure. By using SPCM, we can see a larger increase in the space charge region for samples with DIO when compared to those without DIO. This indicates that the additive improves film morphology leading to increased charge extraction efficiency and decreased recombination.