Stabilizing high-efficiency perovskite solar cells (PSCs) at operating conditions remains an unresolved issue hampering its large-scale commercial deployment. Here, we report a star-shaped polymer to improve charge transport and inhibit ion migration at the perovskite interface. The incorporation of multiple chemical anchor sites in the star-shaped polymer branches strongly controls the crystallization of perovskite film with lower trap density and higher carrier mobility and thus inhibits the nonradiative recombination and reduces the charge-transport loss. Consequently, the modified inverted PSCs show an optimal power conversion efficiency of 22.1% and a very high fill factor (FF) of 0.862, corresponding to 95.4% of the Shockley-Queisser limited FF (0.904) of PSCs with a 1.59-eV bandgap. The modified devices exhibit excellent long-term operational and thermal stability at the maximum power point for 1000 hours at 45°C under continuous one-sun illumination without any significant loss of efficiency.

Interfaces in Sb2S3 thin-film solar cells strongly affect their open-circuit voltage (V OC) and power conversion efficiency (PCE). Finding an effective method of reducing the defects is a promising approach for increasing the V OC and PCE. Herein, the use of an inorganic salt SbCl3 is reported for post-treatment on Sb2S3 films for surface passivation. It is found that a thin SbCl3 layer could form on the Sb2S3 surface and produce higher efficiency cells by reducing the defects and suppressing nonradiative recombination. Through density functional theory calculations, it is found that the passivation of the Sb2S3 surface by SbCl3 occurs via the interactions of Sb and Cl in SbCl3 molecules with S and Sb in Sb2S3, respectively. As a result, incorporating the SbCl3 layer highly improves the V OC from 0.58 to 0.72 V; an average PCE of 6.9 ± 0.1% and a highest PCE of 7.1% are obtained with an area of 0.1 cm2. The achieved PCE is the highest value in the Sb2S3 planar solar cells. In addition, the incorporated SbCl3 layer also leads to good stability of Sb2S3 devices, by which 90% of the initial performance is maintained for 1080 h of storage under ambient humidity (85 ± 5% relative humidity) at room temperature.

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The valence band offsets, ⌬E V , of In 0.17 Al 0.83 N / GaN, In 0.25 Al 0.75 N / GaN, and In 0.30 Al 0.70 N / GaN heterostructures grown by metal-organic vapor phase epitaxy were evaluated by using x-ray photoelectron spectroscopy ͑XPS͒. The dependence of the energy position and the full width at half maximum of the Al 2p spectrum on the exit angle indicated that there was sharp band bending caused by the polarization-induced electric field combined with surface Fermi-level pinning in each ultrathin InAlN layer. The ⌬E V values evaluated without taking into account band bending indicated large discrepancies from the theoretical estimates for all samples. Erroneous results due to band bending were corrected by applying numerical calculations, which led to acceptable results. The evaluated ⌬E V values were 0.2Ϯ 0.2 eV for In 0.17 Al 0.83 N / GaN, 0.1Ϯ 0.2 eV for In 0.25 Al 0.75 N / GaN, and 0.0Ϯ 0.2 eV for In 0.30 Al 0.70 N / GaN. Despite the large decrease of around 1.0 eV in the band gap of InAlN layers according to the increase in the In molar fraction, the decrease in ⌬E V was as small as 0.2 eV. Therefore, the change in band-gap discontinuity was mainly distributed to that in conduction band offset.

The competition between charge recombination and extraction principally affects the fill factor (FF) and power conversion efficiency (PCE) of planar thin-film solar cells. In Sb 2 S 3 thin-film solar cells, the electrocharge recombination and extraction n transport layer (ETL) plays a significant role in electron extraction and determination of Sb 2 S 3 film absorber quality. Herein, a TiO 2 ETL is strategically modified using an inorganic salt zinc halide (i.e., ZnCl 2 , ZnBr 2 , ZnI 2 ), which simultaneously improves the electronic properties of TiO 2 and promotes the growth of Sb 2 S 3 films with larger grain size and higher crystallinity. The experimental results and theoretical calculations further reveal that the zinc halide can interact with TiO 2 and simultaneously bond strongly with the upper Sb 2 S 3 film, which creates a unique pathway for electron transfer, passivates the trap states, and alleviates the recombination losses effectively. As a result, an average PCE of 6.87 ± 0.11% and the highest PCE of 7.08% have been attained with an improved FF from 51.22 to 61.61% after ZnCl 2 introduction. Additionally, introduction of ZnCl 2 helps the unencapsulated devices to maintain 93% of their original performance after 2400 h of storage in a nitrogen-filled glovebox. This work develops an effective route for the optimization of ETLs and defect healing using simple and low-cost inorganic salts.

Tin oxide (SnO2) has recently received increasing attention as an electron transport layer (ETL) in planar perovskite solar cells (PSCs) and is considered a possible alternative to titanium oxide (TiO2). However, planar devices based on pure solution‐processed SnO2 ETL still have hysteresis, which greatly limits the application of SnO2 in high‐efficiency solar cells. Herein, to address this issue, a hybrid ETL of SnO2 and carbon nanotubes (CNTs) is fabricated by a simple thermal decomposing of a mixed solution of SnCl4·5H2O and pretreated CNTs (termed SnO2–CNT). The addition of CNTs can significantly improve the conductivity of SnO2 films and reduce the trap‐state density of SnO2 films, which benefit carrier transfer from the perovskite layer to the cathode. As a result, a high efficiency of 20.33% is achieved in the hysteresis‐free PSCs based on SnO2–CNT ETL, which shows 13.58% enhancement compared with the conventional device (power conversion efficiency = 17.90%).

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