Introduction As an important part of perovskite solar cells, the electron transport layer plays a role in transporting electrons and blocking holes, having an impact on the performance of perovskite cells. ZnO is a promising electron transport layer (ETL) material because of its high electron mobility, easy synthesis, low-temperature preparation and low cost. However, the chemical properties of ZnO are unstable, and the surface defects are easy to form recombination centers, leading to the decline of electron extraction and transfer efficiency, and surface residual groups destroy the perovskite structure and reduce the stability of perovskite materials, resulting in the deterioration of device performance. Therefore, selecting a suitable modification layer to improve the stability of ZnO plays an important role in improving the performance of ZnO and perovskite batteries.Methods ZnO/Zn2SnO4 NAs was prepared on ZnO NAs surface by a spin-coating method to passivate ZnO surface defects and residual groups. ZnO/Zn2SnO4/SnO2 NAs was formed via in-situ growth of a layer of SnO2 by a hydrothermal method to improve the stability of ZnO. The phase and morphology of the heterojunction were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photoelectric performance was measured in electrochemical workstation, in which the photoelectric response ability of the nanoarray was characterized by linear sweep voltammetry. The separation performance of photogenerated electrons and holes in nanoarrays was analyzed via the change of photocurrent. The charge transfer resistance was determined by electrochemical impedance spectroscopy. The conductive type of the semiconductor was determined via the Mott-Schottky test, and the passivation effect of Zn2SnO4 and SnO2 on the ZnO surface defects was reflected by the carrier concentration.Results and discussion The results by XRD, SEM and TEM show that Zn2SnO4 and SnO2 are coated on ZnO nanoarrays. Zn2SnO4 as a protective layer has a superior chemical stability in alkaline environment to prevent direct contact between ZnO and OH- produced by urea hydrolysis, avoiding the corrosion of ZnO. This is beneficial to improving the stability and photoelectric properties of ZnO. The linear scanning voltammetry curves of ZnO, ZnO/SnO2, ZnO/Zn2SnO4 and ZnO/Zn2SnO4/SnO2 NAs at 0-0.6 V vs. RHE under light conditions indicate that ZnO/Zn2SnO4/SnO2 NAs have the maximum photocurrent density. These results demonstrate that the photoelectric response of nanoarrays can be improved via the modification of Zn2SnO4. ZnO/Zn2SnO4 and ZnO/Zn2SnO4/SnO2 NAs modified with Zn2SnO4 exhibit a higher photocurrent. The ZnO/Zn2SnO4/SnO2 NAs photocurrent (i.e., 140 μA·cm-2) is 1.75 times greater than that of ZnO NAs photocurrent (i.e., 80 μA·cm-2). This indicates that the addition of Zn2SnO4 and the construction of double heterojunction have a positive effect on reducing the electron-hole pair recombination phenomenon and improving the photoelectric performance of nanoarray. The charge transfer resistances of ZnO, ZnO/SnO2, ZnO/Zn2SnO4, ZnO/Zn2SnO4/SnO2 NAs measured by electrochemical impedance spectroscopy are 22 403 Ω, 16 854 Ω, 7 018 Ω and 3 131 Ω, respectively. The Zn2SnO4 modified layer reduces a charge transfer resistance via passivating the ZnO surface defects and reducing the scattering effect of the defects on the carriers. The ZnO/Zn2SnO4/SnO2 co-constructed heterojunction structure promotes the separation of electron-hole pairs and electron transport at the interface, further reducing the resistance of photogenerated electrons to transfer at the interface. In the Mott-Schottky test, the carrier concentrations of ZnO, ZnO/Zn2SnO4, ZnO/SnO2, ZnO/Zn2SnO4/SnO2 NAs are 1.22×1019, 2.34×1018, 2.41×1018 and 1.18×1018 cm-3, respectively. ZnO defects are passivated by Zn2SnO4 modification, and the carrier recombination center is reduced. The carrier concentration of ZnO/Zn2SnO4/SnO2 NAs is lower than that of ZnO NAs. ZnO, Zn2SnO4 and SnO2 form a double type II heterojunction with interlaced arrangement of energy level, which drives a transfer of photogenerated electrons from high energy level to low energy level, so that the photogenerated electron-hole pair can be effectively separated at the interface, thus effectively reducing the electron and hole recombination. It also reduces a charge transfer resistance and promotes a photogenerated electron transfer from SnO2 to ZnO. The photoelectric properties of ZnO/Zn2SnO4/SnO2 (i.e., current density, photocurrent and carrier concentration) are improved.Conclusion ZnO NAs surface was coated with Zn2SnO4 nanocrystals by a spin-coating method. Zn2SnO4 reduced the recombination of photo-generated charge carriers at the interface via passivating the defects and residual groups on ZnO NAs surface. Based on ZnO surface defects passivated by Zn2SnO4, a more stable and high-density SnO2 nanoparticle coating layer was in-situ grown on ZnO/Zn2SnO4 NAs by a hydrothermal method, and the double heterojunction was formed with ZnO and Zn2SnO4. The alternating energy level arrangement could improve the separation efficiency of photogenerated charge carriers. The constructed ZnO/Zn2SnO4/SnO2 NAs had higher current density, photocurrent, lower charge transfer resistance and carrier concentration, which could be used as an electron transport layer in perovskite solar cells.