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The energy conversion efficiency (ECE) (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>η</mi></semantics></math></inline-formula>), current density (<i>J_sc</i>), open-circuit voltage (<i>V_oc</i>), and fill factor (<i>ff</i>) of perovskite solar cells were studied by using the transmittance of a nanopatterned mesoporous TiO₂ (mp-TiO₂) thin-film layer. To improve the ECE of perovskite solar cells, a mp-TiO₂ thin-film layer was prepared to be used as an electron transport layer (ETL) via the nanoimprinting method for nanopatterning, which was controlled by the aspect ratio. The nanopatterned mp-TiO₂ thin-film layer had a uniform and well-designed structure, and the diameter of nanopatterning was 280 nm. The aspect ratio was controlled at the depths of 75, 97, 127, and 167 nm, and the perovskite solar cell was fabricated with different depths. The ECE of the perovskite solar cells with the nanopatterned mp-TiO₂ thin-film layer was 14.50%, 15.30%, 15.83%, or 14.24%, which is higher than that of a non-nanopatterned mp-TiO₂ thin-film layer (14.07%). The enhancement of ECE was attributed to the transmittance of the nanopatterned mp-TiO₂ thin-film layer that is due to the improvement of the electron generation. As a result, better electron generation affected the electron density, and <i>J_sc</i> increased the <i>V_oc</i>, and <i>ff</i> of perovskite solar cells.