Over 23% Efficiency Under Indoor Light in Gallium-Doped Zinc Oxide Electron-Transport-Layer-Based Inverted Organic Solar Cell to Power IoT Devices

Inverted structured organic solar cells (OSCs) have recently attracted attention due to their greater stability and performance above conventional structured OSCs. Consequently, under indoor lighting, OSCs have excellent power conversion efficiency (PCE). Indoor OSC may be a useful power source for a variety of electrical devices connected to the Internet of Things network. An inverted structured OSC, the electron transport layer (ETL) is crucial. Inverted OSCs have been constructed with variety of metal oxides-based ETL. Zinc oxide (ZnO) is one of the best options among them because of its high transparency and stability, but its lower electron mobility is the key reason for the ZnO ETL-based inverted OSCs' lower PCE. Moreover, very few studies have been conducted on the application of inverted structured OSCs for indoor light harvesting. We fabricate ZnO and gallium (Ga)-doped ZnO (GZO) ETL-based inverted structured OSCs with an poly [(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo]1,2-b:4,5-b']dithiophene))-alt-(5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl)benzo[1',2'-c:4',5'-c']dithiophene-4,8-dione)]: [6], [6]-phenyl-C71-butyric acid methyl ester (PBDB-T:PC70BM) active layer and evaluate them using a light-emitting diode (LED) (1000 lx). To optimize the doping concentration, we have varied the concentration of Ga in the GZO. The findings demonstrate that only by doping the ETL of the inverted structured OSC, the PCE may be significantly enhanced. Under a 1000-lx LED illumination, the device using undoped ZnO as the ETL shows a maximum of 15.56% PCE. The OSC with GZO as the ETL with an optimized concentration of Ga (2 at.%) exhibits a maximum of 23.42% PCE under a 1000-lx LED.