High‐Performance 3 µm‐Thick Bifacial All‐Inorganic Perovskite Photovoltaics with Fick‐Diffusion‐Engineered Linearly Graded Junction

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Bifacial perovskite solar cells present a promising strategy to enhance power output by capturing light from both sides. A micrometer‐thick perovskite film is highly desired for extending the light absorption path under bifacial illumination conditions, thereby improving overall efficiency. However, this route intensifies the notorious “thick‐thin dilemma,” a challenge posed by the reciprocal constraints between photon coupling and carrier dynamics. While thicker films excel at photon absorption, thinner films are more suitable for long‐range electron transport. Here, these limitations s are addressed by engineering a novel “linear‐graded‐junction” to enhance carrier drift within the perovskite depletion region, avoiding the introduction of additional interface imperfections. A self‐doping effect is initiated through Fick‐diffusion engineering, which generates a strong built‐in electric field and establishes a cascade‐like energy band profile. This results in a remarkable 116% enhancement in carrier mobility and a 195% increase in diffusion length. Consequently, the resulting bifacial PSCs yield a power generation density of 26.03 mW cm −2 in all‐inorganic perovskite on a scale of 3 µm without adding any organic additives, setting a new benchmark in thick‐film PSCs. This approach holds promise for overcoming the long‐standing thick‐thin trade‐off, significantly advancing the industrial viability of high‐performance PSCs.