Perovskite quantum dots (QDs) as a new type of colloidal nanocrystals have gained significant attention for both fundamental research and commercial applications owing to their appealing optoelectronic properties and excellent chemical processability. For their wide range of potential applications, synthesizing colloidal QDs with high crystal quality is of crucial importance. However, like most common QD systems such as CdSe and PbS, those reported perovskite QDs still suffer from a certain density of trapping defects, giving rise to detrimental nonradiative recombination centers and thus quenching luminescence. In this paper, we show that a high room-temperature photoluminescence quantum yield of up to 100% can be obtained in CsPbI perovskite QDs, signifying the achievement of almost complete elimination of the trapping defects. This is realized with our improved synthetic protocol that involves introducing organolead compound trioctylphosphine-PbI (TOP-PbI) as the reactive precursor, which also leads to a significantly improved stability for the resulting CsPbI QD solutions. Ultrafast kinetic analysis with time-resolved transient absorption spectroscopy evidence the negligible electron or hole-trapping pathways in our QDs, which explains such a high quantum efficiency. We expect the successful synthesis of the "ideal" perovskite QDs will exert profound influence on their applications to both QD-based light-harvesting and -emitting devices.

Organic-inorganic hybrid perovskite solar cells have demonstrated unprecedented high power conversion efficiencies in the past few years. Now, the universal instability of the perovskites has become the main barrier for this kind of solar cells to realize commercialization. This situation can be even worse for those tin-based perovskites, especially for CsSnI, because upon exposure to ambient atmosphere the desired black orthorhombic phase CsSnI would promptly lose single crystallinity and degrade to the inactive yellow phase, followed by irreversible oxidation into metallic CsSnI. By alloying CsSnI with CsPbI, we herein report the synthesis of alloyed perovskite quantum dot (QD), CsSnPbI, which not only can be phase-stable for months in purified colloidal solution but also remains intact even directly exposed to ambient air, far superior to both of its parent CsSnI and CsPbI QDs. Ultrafast transient absorption spectroscopy studies reveal that the photoexcited electrons in the alloyed QDs can be injected into TiO nanocrystals at a fast rate of 1.12 × 10 s, which enables a high photocurrent generation in solar cells.

Titanium oxide (TiO2) has been commonly used as an electron transport layer (ETL) of regular‐structure perovskite solar cells (PSCs), and so far the reported PSC devices with power conversion efficiencies (PCEs) over 21% are mostly based on mesoporous structures containing an indispensable mesoporous TiO2 layer. However, a high temperature annealing (over 450 °C) treatment is mandatory, which is incompatible with low‐cost fabrication and flexible devices. Herein, a facile one‐step, low‐temperature, nonhydrolytic approach to in situ synthesizing amino‐functionalized TiO2 nanoparticles (abbreviated as NH2‐TiO2 NPs) is developed by chemical bonding of amino (‐NH2) groups, via TiN bonds, onto the surface of TiO2 NPs. NH2‐TiO2 NPs are then incorporated as an efficient ETL in n‐i‐p planar heterojunction (PHJ) PSCs, affording PCE over 21%. Cs0.05FA0.83MA0.12PbI2.55Br0.45 (abbreviated as CsFAMA) PHJ PSC devices based on NH2‐TiO2 ETL exhibit the best PCE of 21.33%, which is significantly higher than that of the devices based on the pristine TiO2 ETL (19.82%) and is close to the record PCE for devices with similar structures and fabrication procedures. Besides, due to the passivation of the surface trap states of perovskite film, the hysteresis of current–voltage response is significantly suppressed, and the ambient stability of devices is improved upon amino functionalization.

With the potential of achieving high efficiency and low production costs, perovskite solar cells (PSCs) have attracted great attention. However, their unstableness under moist condition has retarded the commercial development. Recently, 2D perovskites have received a lot of attention due to their high moisture resistance. In this work, four quasi 2D quasi perovskites are prepared, then their stability under moist condition is investigated. The surface morphology, crystal structure, optical properties, and photovoltaic performance are measured. Among the four quasi‐2D perovskites, (C6H5CH2NH3)2(FA)8Pb9I28 has the best performance: uniform and dense film, extremely well‐oriented crystal structure, strong absorption, and a high power conversion efficiency (PCE) of 17.40%. The aging tests show that quasi‐2D perovskites are more stable under moist conditions than FAPbI3 is. The (C6H5CH2NH3)2(FA)8Pb9I28 quasi‐2D perovskite devices exhibit high humidity stability, maintaining 80% of the starting PCE after 500 h under 80% relative humidity. Compared with other quasi‐2D perovskites, (C6H5CH2NH3)2(FA)8Pb9I28 has the highest humidity stability, due to their strongest hydrophobicity from C6H5CH2NH3+. This work demonstrates that the properties of perovskite materials can be modified by adding different ammonium salts into FAPbI3. Thus, by introducing ammonium salts with high hydrophobic properties the fabrication of highly efficient and stable 2D PSCs may be possible.

Perovskite solar cells (PSCs) emerging as a promising photovoltaic technology with high efficiency and low manufacturing cost have attracted the attention from all over the world. Both the efficiency and stability of PSCs have increased steadily in recent years, and the research on reducing lead leakage and developing eco-friendly lead-free perovskites pushes forward the commercialization of PSCs step by step. This review summarizes the main progress of PSCs in 2020 and 2021 from the aspects of efficiency, stability, perovskite-based tandem devices, and lead-free PSCs. Moreover, a brief discussion on the development of PSC modules and its challenges toward practical application is provided.

.36%, and 9.18%, which are enhanced by ≈17.5%, 11.6%, and 11.8%, respectively, compared to that of the reference (undoped) devices. The PCE enhancement of the C 3 N 4 QDs doped BHJ-PSC device is found to be primarily attributed to the increase of short-circuit current ( J sc ), and this is confi rmed by external quantum effi ciency (EQE) measurements. The effects of C 3 N 4 QDs on the surface morphology, optical absorption and photoluminescence (PL) properties of the active layer fi lm as well as the charge transport property of the device are investigated, revealing that the effi ciency enhancement of the BHJ-PSC devices upon C 3 N 4 QDs doping is due to the conjunct effects including the improved interfacial contact between the active layer and the hole transport layer due to the increase of the roughness of the active layer fi lm, the facilitated photoinduced electron transfer from the conducting polymer donor to fullerene acceptor, the improved conductivity of the active layer, and the improved charge (hole and electron) transport.

The bi-functional additive of ammonium benzenesulfonate enables the fabrication of low-defect and high-performance perovskite solar cells.

Cubic CsPbI 3 perovskite quantum dots (PQDs) with ideal optoelectronic properties are promising materials for solution-processed photovoltaics. However, their phase stability suffers from the weakly bound surface ligands. Here, we report the adoption of p-mercaptopyridine ligand post-treatment on PQDs and obtained enhanced electronic coupling and cubic phase robustness in comparison with the treatment using analogous o-mercaptopyridine and pyridine ligands. As a result, CsPbI 3 PQDs solar cells achieved an efficiency of 14.25%. More importantly, the device stability was drastically improved, showing decent efficiency after storage under ambient conditions for ∼70 days. We revealed that tuning of the anchoring position can facilely enhance the ligand binding strength and surface coverage, providing efficient ways to significantly improve the performance and stability of PQD-based optoelectronic devices.