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.