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

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.