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Boosted Responsivity and Tunable Spectral Response in B‐Site Substituted 2D Ca2Nb3−xTaxO10 Perovskite Photodetectors

2D Dion‐Jacobson perovskite oxides, featuring fascinating optical and electric properties, exhibit great potential in optoelectronic devices. However, the device sensitivity and spectral selectivity are limited. Herein, B‐site substituted calcium niobate Ca2Nb3−xTaxO10 (x = 0, 0.5, 1, 1.5) nanosheets are prepared by liquid exfoliation. The photodetectors (PDs) based on these nanosheets exhibit tunable spectral response by tailoring the band gap of the nanosheets. All the Ta‐substituted PDs show increased photocurrent and enhanced responsivity, among which the Ca2Nb2.5Ta0.5O10 PD exhibits the optimal performance with a photocurrent of 31.4 µA, a high on–off ratio of 5.6 × 104 and a boosted responsivity of 469.5 A W−1 at 1.0 V toward 295 nm, which is over 7000‐fold higher than that of pristine Ca2Nb3O10 PD. It is proposed that the significantly optimized responsivity is ascribed to the enhanced photoconductive gain that mainly originates from the introduction of the trap states by the B‐site substitution. Nevertheless, excess substitution is detrimental to the responsivity and the response speed. This work demonstrates that the rational control of B‐site substitution tailors the band gap and modulates the charge‐carrier behaviors in 2D perovskite oxides, which provides an effective avenue for achieving high‐performance PDs with tunable spectral response and excellent responsivity.