Polymer surface modification to optimize inverted organic photovoltaic devices under indoor light conditions

The objective of this study is to determine the photovoltaic properties of inverted organic photovoltaic devices (OPVs) that employ indium–tin oxide (ITO) modified by ethoxylated polyethylenimine (PEIE) as an electron-collecting electrode under indoor lighting conditions. Owing to the reduced current generation at low light intensity, possessing a sufficiently large shunt resistance (RP) associated with a low leakage current is of utmost importance for performance maximization. The photovoltaic properties under this lighting condition were optimized by controlling the thickness of the PEIE layers, and the electrical, optical, and surface properties of the PEIE-modified ITO were determined. Inverted OPVs based on poly(3-hexylthiophene)–indene-C60 bisadduct (P3HT–ICBA) with an 8.5-nm-thick PEIE layer yielded a maximum power-conversion efficiency (PCE) of 13.9% under an LED light with a luminance of 500 lx. Meanwhile, the same device showed poor performance with a PCE of 3.1% under 1 sun illumination owing to the insulating nature of PEIE. [Display omitted] •Insulating PEIE-modified ITO was used as an electron-collecting electrode of inverted OPVs.•The spectrum and intensity of indoor light are different from those of 1 sun illumination.•The irradiance of 1 sun is 100 mW/cm2 while that of a 500 lx LED is 0.17 mW/cm2.•The performance under indoor lighting was optimized by controlling the PEIE thickness.•OPVs with 8.5 nm PEIE layer had the highest PCE (13.4%) under 500 lx LED light.