Highly Efficient Inverted Polymer Solar Cells Using an Indium Gallium Zinc Oxide Interfacial Layer

Organic polymer semiconductor-based polymer solar cells (PSCs) are drawing tremendous research interest for their superior electrical, structural, optical, mechanical, and chemical properties. During the last two decades, immense efforts have been made toward the development of PSCs. Generally, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is used as hole transport layer (HTL) of PSCs to improve hole extraction efficiency, but highly acidic PEDOT:PSS reduces device lifetime by destroying indium tin oxide (ITO) electrodes and active layers. To avoid this, some have attempted to develop inverted structured PSCs with different electron transport layers (ETLs); however, the power conversion efficiency (PCE) of these devices is limited owing to low electron mobility of their ETLs. Therefore, an attempt is made to improve the PCE of an inverted-structured PSC by using indium gallium zinc oxide (IGZO) with optimized amount of indium (In), gallium (Ga), and zinc (Zn). Inverted PSCs with ZnO or IGZO (having various molar ratios of In, Ga, and Zn) as ETL with the structure ITO/ETL/PTB7:PC₇₁BM/MoO₃/Al are constructed. The PCE of the inverted PSC can be increased from 6.22% to 8.72% by using IGZO with an optimized weight ratio of In, Ga, and Zn as an ETL.