Organic Solar Cells Based on WO2.72 Nanowire Anode Buffer Layer with Enhanced Power Conversion Efficiency and Ambient Stability

Tungsten oxide as an alternative to conventional acidic PEDOT:PSS has attracted much attention in organic solar cells (OSCs). However, the vacuum-processed WO₃ layer and high-temperature sol-gel hydrolyzed WO_X are incompatible with large-scale manufacturing of OSCs. Here, we report for the first time that a specific tungsten oxide WO_2.72 (W₁₈O₄₉) nanowire can function well as the anode buffer layer. The nw-WO_2.72 film exhibits a high optical transparency. The power conversion efficiency (PCE) of OSCs based on three typical polymer active layers PTB7:PC₇₁BM, PTB7-Th:PC₇₁BM, and PDBT-T1:PC₇₁BM with nw-WO_2.72 layer were improved significantly from 7.27 to 8.23%, from 8.44 to 9.30%, and from 8.45 to 9.09%, respectively compared to devices with PEDOT:PSS. Moreover, the photovoltaic performance of OSCs based on small molecule p-DTS(FBTTh₂)₂:PC₇₁BM active layer was also enhanced with the incorporation of nw-WO_2.72. The enhanced performance is mainly attributed to the improved short-circuit current density (J_sc), which benefits from the oxygen vacancies and the surface apophyses for better charge extraction. Furthermore, OSCs based on nw-WO_2.72 show obviously improved ambient stability compared to devices with PEDOT:PSS layer. The results suggest that nw-WO_2.72 is a promising candidate for the anode buffer layer materials in organic solar cells.