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The stability of perovskite‐based tandem solar cells (TSCs) is the last major scientific/technical challenge to be overcome before commercialization. Understanding the impact of mobile ions on the TSC performance is key to minimizing degradation. Here, a comprehensive study that combines an experimental analysis of ionic losses in Si/perovskite and all‐perovskite TSCs using scan‐rate‐dependent current–voltage (J–V) measurements with drift‐diffusion simulations is presented. The findings demonstrate that mobile ions have a significant influence on the tandem cell performance lowering the ion‐freeze power conversion efficiency from >31% for Si/perovskite and >30% for all‐perovskite tandems to ≈28% in steady‐state. Moreover, the ions cause a substantial hysteresis in Si/perovskite TSCs at high scan speeds (400 s−1), and significantly influence the performance degradation of both devices through internal field screening. Additionally, for all‐perovskite tandems, subcell‐dominated J–V characterization reveals more pronounced ionic losses in the wide‐bandgap subcell during aging, which is attributed to its tendency for halide segregation. This work provides valuable insights into ionic losses in perovskite‐based TSCs which helps to separate ion migration‐related degradation modes from other degradation mechanisms and guides targeted interventions for enhanced subcell efficiency and stability. [ABSTRACT FROM AUTHOR]

Three‐terminal tandem solar cells (3 T TSCs) have recently sparked increasing interest as they feature a lean monolithic device architecture similar to two‐terminal TSCs and, like four‐terminal TSCs, do not require current matching for optimal operation. In this contribution, detailed balance limit calculations for different combinations of top and bottom cell bandgaps are conducted to determine the optimum bandgap pairing and limiting efficiency of 3T TSCs. An experimental realization of a 3T TSC with perovskite and silicon sub‐cells and a combined efficiency of 28.9% is presented and used to derive a realistic parameterization for non‐radiative recombination. Herein, the optimum bandgap pairing and resulting maximum efficiency under voltage‐matched conditions for voltage‐matching ratios of 1:2 and 2:3, which is relevant for stringing and module integration of 3T TSCs, are further determined. To this end, non‐radiative recombination is incorporated in the model and quantified by matching theoretical open‐circuit voltages and those of real‐world high‐efficiency solar cells based on different absorber materials (and thus bandgaps), including the perovskite top cell of the best in‐house 3T TSC. [ABSTRACT FROM AUTHOR]

Improved stability and efficiency of two-terminal monolithic perovskite-silicon tandem solar cells will require reductions in recombination losses. By combining a triple-halide perovskite (1.68 electron volt bandgap) with a piperazinium iodide interfacial modification, we improved the band alignment, reduced nonradiative recombination losses, and enhanced charge extraction at the electron-selective contact. Solar cells showed open-circuit voltages of up to 1.28 volts in p-i-n single junctions and 2.00 volts in perovskite-silicon tandem solar cells. The tandem cells achieve certified power conversion efficiencies of up to 32.5%. [ABSTRACT FROM AUTHOR]

In monolithic tandem solar cells, current−voltage (J−V) characteristics of subcells provide invaluable information about their quality and tandem operation. However, accessing the subcell J−Vs is challenging and requires sophisticated spectral methods. Herein, a customized, bichromatic light emitting diode setup (BCLED) for in‐depth analysis of tandem solar cells, suitable for subcell operation analysis, and long‐term stability testing is presented. For this, two spectrally independent LED arrays are used to selectively bias the two subcells. The power of the developed setup is demonstrated by successfully disentangling the tandem J−V curve into subcell J−V curves. The method is based on a one‐diode model for each subcell and is validated by electrical simulations. Afterward, it is used on a fabricated 27.6% efficient perovskite/silicon tandem device, resulting in great agreement with the measured J−V curve. Therefore, the BCLED setup is a versatile tool, suitable for subcell characteristics and long‐term stability analysis of tandem solar cells. [ABSTRACT FROM AUTHOR]

Tandem solar cells that pair silicon with a metal halide perovskite are a promising option for surpassing the single-cell efficiency limit. We report a monolithic perovskite/silicon tandem with a certified power conversion efficiency of 29.15%. The perovskite absorber, with a bandgap of 1.68 electron volts, remained phase-stable under illumination through a combination of fast hole extraction and minimized nonradiative recombination at the hole-selective interface. These features were made possible by a self-assembled, methyl-substituted carbazole monolayer as the hole-selective layer in the perovskite cell. The accelerated hole extraction was linked to a low ideality factor of 1.26 and single-junction fill factors of up to 84%, while enabling a tandem open-circuit voltage of as high as 1.92 volts. In air, without encapsulation, a tandem retained 95% of its initial efficiency after 300 hours of operation. [ABSTRACT FROM AUTHOR]