Influence of interfacial modification by conjugated small molecules in large-scale spray-coated inverted organic solar cells

Incorporating conjugated small molecules comprising electron-withdrawing and -donating moieties as interfacial modifiers (IMs) between the electron transporting layer (ETL) and photoactive layer offers a promising strategy for fabrication of high-performance inverted organic solar cells (iOSCs). This approach effectively reduces charge trapping and recombination at the interface between the ETL and the photoactive layer, leading to improved device performance and stability. The introduction of IMs resulted in the transformation of the hydrophilic ZnO ETL surface to a hydrophobic state. When employed as the ETL in small-area iOSCs, IM/ZnO demonstrated a remarkable maximum power conversion efficiency (PCE) of 3.8% accompanied by enhanced open-circuit voltage (V_OC) and fill factor (FF) values. The significant contribution of the IM was evident in achieving a uniform film deposition and complete coverage of the spray-coated photoactive P3HT:PCBM layer in large-area applications. Despite an observed decrease in average performance of iOSC devices as the photoactive area increased, inclusion of IM/ZnO ETL in these iOSCs led to average PCE values that were 1.3–2.9 times higher with reduced variability compared to iOSCs utilizing a pristine ZnO ETL. This highlighted the potential for conjugated small-molecule IM-modified ZnO as a promising ETL candidate for achieving high-performance and scalable organic electronics.