Significant progress has been achieved in improving the power conversion efficiency (PCE) of perovskite solar cells (PSCs) for a decade, but the long-term stability is still underdeveloped. In a regular PSC structure, 2,2′,7,7′-tetrakis­(N,N-di-p-methoxyphenylamine)­9,9′-spirobifluorene (Spiro-OMeTAD) with Li additives and metal electrodes are widely adopted, which leads to facile degradation under device operating conditions because of ion migration. Herein, we show an interface-engineered stabilization approach to prevent ion migration in PSCs enabled by amorphous (a)-TiO2 capable of hole transfer grown by atomic layer deposition (ALD). This layer prevents ion migration of Li additives with consequent aggregation as well as metal electrode diffusion into the perovskite layer. Furthermore, the combined layers of Spiro-OMeTAD/a-TiO2 unprecedentedly promote device efficiency, which is further verified with other organic hole transport layers. Finally, the operational stability of the TiO2-PSC is substantially improved in comparison to that of the control PSC.

Insufficient charge extraction at the interfaces between light‐absorbing perovskites and charge transporting layers is one of the drawbacks of state‐of‐the‐art perovskite solar cells. Surface treatments and/or interface engineering are necessary to approach the Shockley–Queisser limit. In this work, novel 2D layered perovskites, such as CHA2PbI4 (CHAI = cyclohexylammonium iodide) and CHMA2PbI4 (CHMAI = cyclohexylmethylammonium iodide), are introduced in between 3D perovskites and hole transporting layers by a simple solution process and the 2D/3D perovskite heterojunction is formed and confirmed. Spontaneous photoluminescence quenching is observed by efficient hole extraction with a favorable valence band alignment. The charge extraction ability and recombination are directly measured by the transient photocurrent and photovoltage. Moreover, the interface resistance of the devices significantly is decreased to 30% as compared to devices without 2D perovskites. As a result, the devices with 2D/3D perovskite heterojunction exhibit improved power conversion efficiency (PCE) from 20.41% to 23.91% primarily because of the increased open‐circuit voltage (1.079 to 1.143 V) and fill factor (78.22% to 84.25%). The results provide a detailed insight into hole extraction and high PCEs with the formation of a 2D/3D perovskite heterojunction.

MoO3 has great potential as an electrode for lithium‐ion batteries due to its unique layered structure that can host Li+. Despite high theoretical capacity (≈1117 mAh g−1), MoO3 is not widely used simply because of poor rate capability due to lower electronic conductivity and severe pulverization. The Li‐storage mechanism in MoO3 is also still unclear. Herein, oxygen‐vacancy‐controlled MoO3 is used without any additional binders and conductive materials to directly examine the Li‐storage mechanism on MoO3−x. Li‐storage capacity based on the reversible formation/decomposition of solid‐electrolyte interphase (SEI) films and the transformation of MoO3−x to amorphous Li2MoO3 is demonstrated. The surfaces of MoO3−x are conjugated with Cu2O nanoparticles via annealing at 200 °C. Cu2O acts as an effective catalyst for the formation of SEI films and the reversible reaction of MoO3−x with Li+ ions. As a result, Cu2O@MoO3−x exhibits a charge capacity of 1100 mAh g−1 after the second cycle and maintains a high reversible capacity, whereas MoO3−x exhibits a charge capacity of 900 mAh g−1 and fades to 590 mAh g−1 after 100 cycles at 1 A g−1.

Perovskite solar cells (PSCs) have attracted tremendous interest due to their outstanding intrinsic photovoltaic properties, such as absorption coefficients, exciton binding energies, and long carrier lifetimes. Although the power conversion efficiency (PCE) of PSCs is close to the Si solar cells’ PCE, device stability remains a challenge. In particular, the device stability is more critical in n-i-p normal structured PSCs, which show a higher efficiency than p-i-n inverted ones, simply because of the much lower stability of 2,2′,7,7′-tetrakis­[N,N-di­(4-methoxyphenyl)­amino]-9,9′-spirobifluorene (Spi). To prevent the devices from degrading performances arising both from perovskite’s degradation and Spi instability, we prepare atomic layer deposition (ALD)-grown transition metal oxides for hole transport with efficient n-i-p PSCs. We demonstrate low-temperature (T dep = 45 °C)-grown amorphous ALD-V2O5–x with oxygen-deficient traps on top of Spi as an interlayer, which prevents the devices’ degradation in performance. By blocking moisture and oxygen, ALD-V2O5–x was able to greatly improve the devices’ stability by preserving the photovoltaic α-FAPbI3 phase while suppressing both Li ion diffusion from the additive and Au ions from the electrode. As a result, we successfully fabricate PSCs with passivation/hole-transporting bifunctional Spi/ALD-V2O5–x interlayers without sacrificing photovoltaic performances, and the device stability is significantly improved.

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