Exceeding 2.2 V Open-Circuit Voltage in Perovskite/Organic Tandem Solar Cells via Multi-Functional Hole-Selective Layer

Abstract

Perovskite/organic tandem solar cells (POTSCs) are gaining attention due to their potential to surpass the Shockley-Queisser limit through the reduction of thermalization losses. However, wide bandgap perovskite solar cells (WBG PSCs), which function as top cells of POTSCs, still suffer from significant open-circuit voltage (VOC) loss, which limits the efficiency improvement of POTSCs. Here, we report a multi-functional hole-selective layer (mHSL) via blending two functionalized molecules (4-(3,6-diiodo-9H-carbazol-9-yl)butyl)phosphonic acid (36ICzC4PA) and (4-(3,6-dimethoxy-9H-carbazol-9-yl)butyl)phosphonic acid (36MeOCzC4PA). The blending of the two highly aggregating molecules demicellizes to form a uniform and high-coverage mHSL, which plays multiple roles of (i) providing the homogeneous surface potential of the HSL, (ii) extracting hole efficiently, (iii) enhancing the crystallinity of the perovskite on mHSL, and (iv) suppressing both lattice strain and phase segregation. Thus, it maximizes the VOC in POTSCs. Implementing mHSL on WBG PSCs enables a power conversion efficiency (PCE) of 18.85% with a notable VOC of 1.366 V. When applied to fabricated POTSCs, the PCE reached 24.73% (certified 24.19%) with a record-high VOC and fill factor (FF) of 2.216 V and 84.07%, respectively. Furthermore, encapsulated POTSCs exhibit excellent photostability, retaining 80% of their initial PCEs after maximum power point (MPP) tracking under 1-sun illumination in ambient conditions for 305 hours. In addition, unencapsulated POTSCs demonstrate notable thermal stability, retaining 82% of their initial PCEs after exposure to 65℃ in N2 conditions for 500 hours.