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

A multi-functional hole-selective layer (mHSL) is proposed to yield potential homogenization of the HSL and crystallinity of an atop wide bandgap (WBG) perovskite. This enhances hole extraction and suppresses lattice strain and phase segregation. A resulting perovskite/organic tandem solar cell (POTSC) exhibits an impressive power conversion efficiency of 24.73%, demonstrating excellent stability during maximum power point (MPP) tracking or thermal-stress conditions.

Abstract

Perovskite/organic tandem solar cells (POTSCs) are promising candidates for surpassing the Shockley-Queisser limit through 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 (V _OC) losses, limiting efficiency improvement of POTSCs. Here, a multi-functional hole-selective layer (mHSL) is reported via blending two functionalized self-assembled monolayer (SAM) 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 molecules plays multiple roles: i) Suppressing micelle formation of SAM molecules, ii) optimizing energy level alignment with homogeneous and highly covered SAMs, iii) enhancing crystallinity and orientation of perovskite through interaction with SAM materials, and iv) suppressing both lattice strain and phase segregation. Implementing mHSL on WBG PSCs enables a power conversion efficiency (PCE) of 18.85% with a notable V _OC of 1.366 V. When integrated into POTSCs, the PCE reached 24.73% (certified 24.19%) with record-high V _OC and fill factor (FF) of 2.216 V and 84.07%, respectively. Furthermore, POTSCs exhibit excellent photo- and thermal stabilities, retaining ≈80% of their initial PCEs after maximum power point (MPP) tracking under 1-sun illumination in ambient conditions for 305 h or exposure to 65 °C in N₂ conditions for 500 h.