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External encapsulation technique as a straightforward craft process has been adopted to prevent the infiltration of moisture and oxygen, thereby improving environmental stabilities of lead halide perovskite solar cells (PSCs). However, irreversible light‐induced degradation originating from various vacancies and ion diffusion or migration inside the device cannot be efficiently solved by external encapsulation. Herein, an internal encapsulation strategy by introducing NbCl5 at the buried tin oxide/perovskite interface and spin‐casting n‐butylammonium bromide on top of perovskite is developed to comprehensively passivate the vacancies and hence block the channels for ion diffusion or migration. The internal encapsulation strategy results in better homogeneous electron transport layer and effective vacancy passivation at the buried interface and simultaneously generates a more homogeneous, better crystallized perovskite in the vertical direction with significantly reduced residual PbI2. Furthermore, fewer oxygen vacancies and formation of ultrathin Nb2O5 lead to a better interfacial energy level alignment for electron transfer. As a result, power conversion efficiency (PCE) of the resulting PSCs is as high as 24.01%. More importantly, the device demonstrates an excellent stability, retaining 88% of its initial PCE at its maximum power point tracking measurement (under 100 mW cm–2 white light illumination at ≈55 °C temperature, in N2 atmosphere) after 1000 h. [ABSTRACT FROM AUTHOR]

Antireflection (AR) film is a widely used technology to enhance the performance of photovoltaic devices that require transparent electrodes in the photovoltaic industry. At present, several AR films including monolayer MgF2 or multilayered composite films, textured polydimethylsiloxane (PDMS) and porous SiO2 have been successfully applied due to their excellent properties. Nevertheless, all of the above-mentioned AR films have some minor drawbacks to overcome, for instance, the cost or thermal durability. Herein, we report a cost-effective and low-temperature method to fabricate a mesoporous aluminum oxide (meso-Al2O3) layer as the AR coating with high thermal durability, which will meet the fabrication condition of various photovoltaic devices. Briefly, the process begins at magnetron sputtering a compact Al2O3 film, which shows no AR effect, followed by a hot water treatment at 80 °C to turn the compact film into a mesoporous film with graded-index and AR effect. The application of meso-Al2O3 AR film enhances the maximum transmittance of our laboratory-used fluorine-doped tin oxide (FTO) from 84% to 89%, which is in good agreement with our theoretical simulation named graded-index approximation. Taking perovskite solar cells (PSCs) as an example, planar PSCs with meso-Al2O3 AR film deliver excellent photon conversion efficiency of 21.5%, which is higher than that of cells without meso-Al2O3 AR film (20.9%). [ABSTRACT FROM AUTHOR]

Tin oxide (SnO 2) as an electron transport layer (ETL) has made impressive achievements in planar-structure heterojunction perovskite solar cells (PSCs). However, the improvement of the SnO 2 quality, connected with its trap density, electrical conductivity and band energy alignment, is still worth concerning. The quality of the SnO 2 film especially from wet coating techniques is quite sensitive to the environment conditions in the preparation process thus leading to poor repeatability. High repeatability of every functional layer fabrications is one of the basic requirements toward commercialization for PSCs. Herein, we add hydrogen peroxide (H 2 O 2) into the SnO 2 precursor solution (denoted as H 2 O 2 –SnO 2) to enable the quality improvement of ETL. The resultant H 2 O 2 –SnO 2 film exhibits less trap density, improved electrical conductivity, outstanding film fabrication repeatability and better energy level alignment, leading to significantly higher charge carrier extraction and reduced device hysteresis effect. By employing H 2 O 2 –SnO 2 ETL, PSCs with excellent repeatability and performance uniformity deliver a champion power conversion efficiency (PCE) of 22.15% with negligible hysteresis, and show impressive long-term stability. This research paves a new way for the further performance enhancement of planar PSCs and the higher quality modified SnO 2 may find applications in other opto-electronic devices. • Hydrogen peroxide was introduced to passivate defects of SnO 2 as ETL in PSCs. • The PSCs using hydrogen peroxide-modified SnO 2 ETL exhibited better repeatability. • The PSCs of hydrogen peroxide-modified SnO 2 ETL delivered a PCE of 22.15%. • The stability of PSCs with hydrogen peroxide-modified SnO 2 ETL was prolonged. [ABSTRACT FROM AUTHOR]