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 (SRH) recombination and 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 optoelectronic properties with the control HTL. The TBMP⁺TFSI⁻-doped spiro-MeOTAD HTL enhances the photoluminescence quantum efficiency (PLQY) and carrier lifetime by reducing interfacial defects, improving the open circuit voltage (V_OC) and fill factor (FF), in agreement with our detailed simulation results. 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.