Effect of fullerene substituent on low-light characteristics of polymer: fullerene bulk heterojunction solar cells

Abstract

A halogen-free solvent 1,2,4-trimethylbenzene dissolves both unmodified fullerenes and conjugated polymers such as PTB7-Th. This unique feature enables the study on the effect of the substituent of fullerene in polymer:fullerene bulk heterojunction solar cells under low-light illumination. Although the power conversion efficiency (PCE) of the PTB7-Th:C₇₀ solar cell was higher than that of the PTB7-Th:C₇₀-PCBM solar cell under one sun illumination, the latter showed higher PCE than the former under 10⁻³ sun illumination. This result comes from the fact that C₇₀-PCBM yields higher open-circuit voltage (V_OC) at one sun and smaller dependence of V_OC on illumination light intensity than C₇₀.

Keywords:

• Bulk heterojunction composite
• fullerene substituent
• indoor light energy harvesting
• organic solar cell

Additional information

Funding

This work was partially supported by the Iwatani Naoji Foundation’s Research Grant and JSPS KAKENHI Grant Number JP18K04241.