Photovoltaic performance improvement of inverted type organic solar cell by co-introducing isopropanol and carbon quantum dots in photoactive layer

The photovoltaic performance of organic solar cells has been improved previously by the introduction of solvent additive and carbon quantum dots (CQDs) in the photoactive layer. In this study, the photoactive layer consisted of poly (3-hexylthiophene) (P3HT) as donor and (6,6)-phenyl-C₆₁-butyric acid methyl ester (PCBM) as acceptor was used. The CQDs were first dispersed in isopropanol (IPA) before being incorporated into the photoactive layer solution. The structure of the organic solar cell was fluorine-doped tin oxide (FTO)/ZnO/P3HT:PCBM:CQDs:IPA/Ag. Under 1-sun illumination, the device with 2 wt% CQDs/40 vol.% IPA exhibited the highest power conversion efficiency, an increment of almost 100% relative to that of pristine device. It is believed that the introduction of isopropanol additive mainly improves the phase separation and P3HT crystallinity, whereas the CQDs contributes to the enhancement of optical absorption, exciton dissociation and charge transport of the solar cell. However, under indoor white LED illumination, it is worth noting that the device with a pristine photoactive layer exhibited the best photovoltaic performance compared to the devices with IPA and CQDs, possibly due to the less dominant effect of charge recombination under weak illumination intensity.