Lead halide perovskite solar cells (PSCs) with the high power conversion efficiency (PCE) typically use mesoporous metal oxide nanoparticles as the scaffold and electron-transport layers. However, the traditional mesoporous layer suffers from low electron conductivity and severe carrier recombination. Here, antimony-doped tin oxide nanorod arrays are proposed as novel transparent conductive mesoporous layers in PSCs. Such a mesoporous layer improves the electron transport as well as light utilization. To resolve the common problem of uneven growth of perovskite on rough surface, the dynamic two-step spin coating strategy is proposed to prepare highly smooth, dense, and crystallized perovskite films with micrometer-scale grains, largely reducing the carrier recombination ratio. The conductive mesoporous layer and high-quality perovskite film eventually render the PSC with a remarkable PCE of 20.1% with excellent reproducibility. These findings provide a new avenue to further design high-efficiency PSCs from the aspect of carrier transport and recombination.

In planar perovskite solar cells, it is vital to engineer the extraction and recombination of electron-hole pairs at the electron transport layer/perovskite interface for obtaining high performance. This study reports a novel titanium oxide (TiO ) bilayer with different Fermi energy levels by combing atomic layer deposition and spin-coating technique. Energy band alignments of TiO bilayer can be modulated by controlling the deposition order of layers. The TiO bilayer based perovskite solar cells are highly efficient in carrier extraction, recombination suppression, and defect passivation, and thus demonstrate champion efficiencies up to 16.5%, presenting almost 50% enhancement compared to the TiO single layer based counterparts. The results suggest that the bilayer with type II band alignment as electron transport layers provides an efficient approach for constructing high-performance planar perovskite solar cells.

In the planar perovskite solar cells (PSCs), the electron transport layer (ETL) plays a critical role in electron extraction and transport. Widely utilized TiO2 ETLs suffer from the low conductivity and high surface defect density. To address these problems, for the first time, two types of ETLs based on TiO2 phase junction are designed and fabricated distributed in the opposite space, namely anatase/rutile and rutile/anatase. The champion efficiency of PSCs based on phase junction ETL is over 15%, which is much higher than that of cells with single anatase (9.8%) and rutile (11.8%) TiO2 as ETL. The phase junction based PSCs also demonstrated obviously reduced hysteresis. The enhanced performance is discussed and mainly ascribed to the excellent capability of carrier extraction, defect passivation, and reduced recombination at the ETL/perovskite interface. This work opens a new phase junction ETL strategy toward interfacial energy band manipulation for improved PSC performance.

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The quality of the perovskite film has a vital influence on the performance of perovskite solar cells and it is quite desirable to simultaneously manipulate the crystallization and morphology of the perovskite film. In this study, conventional PbI2 is replaced with a PbI2/I2 mixed precursor during the first step of sequential deposition, causing the formation of a PbI2 porous nanostructure. By changing the content of I2 in the precursor, the morphology of the PbI2 film as well as the resulting perovskite film can be successfully modulated. With an optimal content of I2, a high‐quality perovskite film with a pure phase and smooth surface can be achieved. As a result, the conversion efficiency of perovskite solar cells using a PbI2/I2 mixed precursor can be as high as 18.63%, compared to 16.89% for the reference device through traditional sequential deposition with a pure PbI2 precursor.

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