Bandgap Tunable Transparent Perovskite Solar Cells for 4T Si/perovskite Tandem Photovoltaics with PCE > 30% via Rational Interface Management

Abstract

Silicon/perovskite tandem solar cells are predominantly recognized as a promising next-generation photovoltaic technology. The precise control of interfacial defects with appropriate energy level alignment between charge transport layers (CTLs) and the perovskite absorber is a crucial factor influencing the overall photovoltaic performance of perovskite solar cells (PSCs). This study investigates the substitution of conventional Lithium bis(trifluoromethane)sulfonimide (LiTFSI)- and 4-tert-butylpyridine (t-BP)-doped Spiro-MeOTAD with a post-oxidation-free, ion-modulated Spiro-MeOTAD hole transport layer (HTL) for tunable bandgap transparent PSCs. The incorporation of 4-tert-butyl-1-methylpyridinium bis(trifluoromethanesulfonyl)imide (TBMP⁺TFSI⁻) enables reduced Shockley-Read Hall recombination with controlled work function tuning, leading to enhanced quasi-Fermi level splitting (QFLS). Three different perovskite compositions are employed, with perovskite 2 (1.61 eV) demonstrating optimal performance with both control and ion-modulated Spiro-MeOTAD, resulting in minimal photovoltaic performance deviations. In contrast, perovskite 1 (1.52 eV) and perovskite 3 (1.72 eV) exhibit suboptimal opto-electronic properties with the control HTL. The TBMP⁺TFSI⁻-doped Spiro-MeOTAD HTL enhances photoluminescence quantum efficiency and carrier lifetime by reducing interfacial defects, improving V_OC, and fill factor (FF). Integrating the optimized PSCs with an n-type tunnel oxide passivated contact (n-TOPCon) silicon (Si) solar cell in a 4-terminal (4T) tandem configuration achieves a power conversion efficiency (PCE) of 30.2%, highlighting the potential of ion-modulated Spiro-MeOTAD for efficient and stable tandem solar cells.