Tin oxide (SnO2) has recently emerged as a promising electron transport layer for perovskite solar cells (PSCs) in light of the material’s optical and electronic properties and its low-temperature processing. However, SnO2 films are prone to surface defect formation, which results in energy loss in PSCs. We report that surface treatment using ammonium fluoride (NH4F) leads to reduced surface defects and that it also induces chemical doping of the SnO2 substrate simultaneously. The effects of NH4F treatment on SnO2 properties are revealed by surface chemical analysis, computational studies, and energy level investigations, and PSCs with the treatment achieve photovoltaic performance of 23.2% in light of higher voltage than in relevant controls.

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The open‐circuit voltage (Voc) of perovskite solar cells is limited by non‐radiative recombination at perovskite/carrier transport layer (CTL) interfaces. 2D perovskite post‐treatments offer a means to passivate the top interface; whereas, accessing and passivating the buried interface underneath the perovskite film requires new material synthesis strategies. It is posited that perovskite ink containing species that bind strongly to substrates can spontaneously form a passivating layer with the bottom CTL. The concept using organic spacer cations with rich NH2 groups is implemented, where readily available hydrogens have large binding affinity to under‐coordinated oxygens on the metal oxide substrate surface, inducing preferential crystallization of a thin 2D layer at the buried interface. The passivation effect of this 2D layer is examined using steady‐state and time‐resolved photoluminescence spectroscopy: the 2D interlayer suppresses non‐radiative recombination at the buried perovskite/CTL interface, leading to a 72% reduction in surface recombination velocity. This strategy enables a 65 mV increase in Voc for NiOx based p–i–n devices, and a 100 mV increase in Voc for SnO2‐based n–i–p devices. Inverted solar cells with 20.1% power conversion efficiency (PCE) for 1.70 eV and 22.9% PCE for 1.55 eV bandgap perovskites are demonstrated.

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Emerging technologies such as autonomous driving and augmented reality rely on light detection and ranging (LiDAR based on time of flight (ToF). [3] This requires sensitive and ultrafast photodetection of infrared light with nanoseconds' resolution. [4] Today, this is achieved in the near-infrared (NIR) using indirect bandgap silicon detectors-limited by silicon's low absorption coefficient-and, at longer wavelengths, using epitaxially grown semiconductors such as III-Vs and Hg 1−x Cd x Te. [5,6] Colloidal quantum dots (CQDs) are of interest given by their low-temperature solution processing, which allows them to be integrated with silicon electronic readout and signal-processing circuitry. [7][8][9][10] Their bandgap is size-tuned over a wide range of wavelengths. PbS, for example, has a widely programmable absorption onset covering the visible and shortwavelength infrared (SWIR); [11,12] however, its high permittivity, stemming from its ionic character-ε r = 180 for bulk PbS [13] slows charge extraction both for bulk [14] and CQD photodiodes [15] due to screening and capacitance effects.Colloidal quantum dots (CQDs) are promising materials for infrared (IR) light detection due to their tunable bandgap and their solution processing; however, to date, the time response of CQD IR photodiodes is inferior to that provided by Si and InGaAs. It is reasoned that the high permittivity of II-VI CQDs leads to slow charge extraction due to screening and capacitance, whereas III-Vs-if their surface chemistry can be mastered-offer a low permittivity and thus increase potential for high-speed operation. In initial studies, it is found that the covalent character in indium arsenide (InAs) leads to imbalanced charge transport, the result of unpassivated surfaces, and uncontrolled heavy doping. Surface management using amphoteric ligand coordination is reported, and it is found that the approach addresses simultaneously the In and As surface dangling bonds. The new InAs CQD solids combine high mobility (0.04 cm 2 V −1 s −1 ) with a 4× reduction in permittivity compared to PbS CQDs. The resulting photodiodes achieve a response time faster than 2 nsthe fastest photodiode among previously reported CQD photodiodes-combined with an external quantum efficiency (EQE) of 30% at 940 nm.