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Tandem solar cells (TSCs) comprising stacked narrow‐bandgap and wide‐bandgap subcells are regarded as the most promising approach to break the Shockley–Queisser limit of single‐junction solar cells. As the game‐changer in the photovoltaic community, organic–inorganic hybrid perovskites became the front‐runner candidate for mating with other efficient photovoltaic technologies in the tandem configuration for higher power conversion efficiency, by virtue of their tunable and complementary bandgaps, excellent photoelectric properties, and solution processability. In this review, a perspective that critically dilates the progress of perovskite material selection and device design for perovskite‐based TSCs, including perovskite/silicon, perovskite/copper indium gallium selenide, perovskite/perovskite, perovskite/CdTe, and perovskite/GaAs are presented. Besides, all‐inorganic perovskite CsPbI3 with high thermal stability is proposed as the top subcell in TSCs due to its suitable bandgap of ≈1.73 eV and rapidly increasing efficiency. To minimize the optical and electrical losses for high‐efficiency TSCs, the optimization of transparent electrodes, recombination layers, and the current‐matching principles are highlighted. Through big data analysis, wide‐bandgap perovskite solar cells with high open‐circuit voltage (Voc) are in dire need in further study. In the end, opportunities and challenges to realize the commercialization of TSCs, including long‐term stability, area upscaling, and mitigation of toxicity, are also envisioned.

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In this work, hafnium oxide (HfO 2 ) thin films are deposited on p-type Si substrates by remote plasma atomic layer deposition on p-type Si at 250 °C, followed by a rapid thermal annealing in nitrogen. Effect of post-annealing temperature on the crystallization of HfO 2 films and HfO 2 /Si interfaces is investigated. The crystallization of the HfO 2 films and HfO 2 /Si interface is studied by field emission transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and atomic force microscopy. The experimental results show that during annealing, the oxygen diffuse from HfO 2 to Si interface. For annealing temperature below 400 °C, the HfO 2 film and interfacial layer are amorphous, and the latter consists of HfO 2 and silicon dioxide (SiO 2 ). At annealing temperature of 450-550 °C, the HfO 2 film become multiphase polycrystalline, and a crystalline SiO 2 is found at the interface. Finally, at annealing temperature beyond 550 °C, the HfO 2 film is dominated by single-phase polycrystalline, and the interfacial layer is completely transformed to crystalline SiO 2 .

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This study prepared aluminum and gallium co-doped zinc oxide (AGZO) thin films using pulsed direct current magnetron sputtering, and studied the electrical properties, transmittance, effects of texturing, and applicability as the front contact for a-Si:H solar cells. Textured ZnO:Al (AZO) and ZnO:Ga (GZO) thin films were also compared with AGZO thin film to evaluate their performance as front contacts. Experimental results show that AGZO films with the highest figure of merit φ TC value (24.64 × 10 −3 −1) were obtained at Al and Ga doping concentrations of 0.54 wt% and 1.165 wt%, respectively. The textured AGZO films used as the front contact in a-Si:H solar cells achieved the following results: V OC = 0.77 V, J SC = 16.5 mA/cm 2 , FF = 59%, and conversion efficiency of 7.53%. AZO and GZO films have better electrical properties than AGZO film; however, AGZO film has superior transmittance in the near-infrared (NIR) region and higher J SC , conversion efficiency and external quantum efficiency (EQE) than AZO and GZO films under a similar haze value.

In this study, aluminum oxide (Al 2 O 3 ) films were prepared by a spatial atomic layer deposition using deionized water and trimethylaluminum, followed by oxygen (O 2 ), forming gas (FG), or two-step annealing. Minority carrier lifetime of the samples was measured by Sinton WCT-120. Field-effect passivation and chemical passivation were evaluated by fixed oxide charge ( Q f ) and interface defect density ( D it ), respectively, using capacitance-voltage measurement. The results show that O 2 annealing gives a high Q f of − 3.9 × 10 12 cm −2 , whereas FG annealing leads to excellent Si interface hydrogenation with a low D it of 3.7 × 10 11 eV −1 cm −2 . Based on the consideration of the best field-effect passivation brought by oxygen annealing and the best chemical passivation brought by forming gas, the two-step annealing process was optimized. It is verified that the Al 2 O 3 film annealed sequentially in oxygen and then in forming gas exhibits a high Q f (2.4 × 10 12 cm −2 ) and a low D it (3.1 × 10 11 eV −1 cm −2 ), yielding the best minority carrier lifetime of 1097 μs. The SiN x /Al 2 O 3 passivation stack with two-step annealing has a lifetime of 2072 μs, close to the intrinsic lifetime limit. Finally, the passivated emitter and rear cell conversion efficiency was improved from 21.61% by using an industry annealing process to 21.97% by using the two-step annealing process.