Ternary-Metal Sn-Pb-Zn Perovskite to Reconstruct Top Surface for Efficient and Stable Less-Pb Perovskite Solar Cells.

Though Sn-Pb alloyed perovskite solar cells (PSCs) achieved great progress, there is a dilemma to further increase Sn for less-Pb requirement. High Sn ratio (>70%) perovskite exhibits nonstoichiometric Sn:Pb:I at film surface to aggravate Sn2+ oxidation and interface energy mismatch. Here, ternary metal alloyed (FASnI3 )0.7 (MAPb1- x Znx I3 )0.3 (x = 0-3%) is constructed for Pb% < 30% perovskite. Zn with smaller ionic size and stronger ionic interaction than Sn/Pb assists forming high-quality perovskite film with ZnI6 4- enriched at surface to balance Sn:Pb:I ratio. Differing from uniform bulk doping, surface-rich Zn with lower lying orbits pushes down the energy band of perovskite and adjusts the interface energy for efficient charge transfer. The alloyed PSC realizes efficiency of 19.4% at AM1.5 (one of the highest values reported for Pb% < 30% PSCs). Moreover, stronger bonding of Zn─I and Sn─I contributes to better durability of ternary perovskite than binary perovskite. This work highlights a novel alloy method for efficient and stable less-Pb PSCs.

Low-temperature solution-processed LaNiO3 hole-transport layer for UV-stable inverted perovskite solar cells.

We report a solution-processing method to prepare an inorganic LaNiO3 (LNO) hole-transport layer (HTL) under low temperature (<150 °C) for the first time. The inverted PSCs prepared with LNO exhibit high UV-stability and promising efficiency (17.15%). Our preliminary results show great potential for LNO HTL in the fabrication of efficient and photostable inverted perovskite solar cells (PSCs).

Regulating the Interplay at the Buried Interface for Efficient and Stable Carbon-Based CsPbI2Br Perovskite Solar Cells.

Buried interface modification is promising for preparing high-performance perovskite solar cells (PSCs) by improving the film quality and adjusting the interfacial energy level alignment. In this work, multifunctional ethylenediaminetetraacetic acid diammonium (EAD)-modulated ZnO is employed as an effective buried interface to regulate the interplay between SnO2 and CsPbI2Br in carbon-based inorganic PSCs (C-IPSCs). The burying of EAD into the ZnO interlayer not only enhances the photoelectric properties of ZnO by passivating oxygen defects but also adjusts the energy level alignment of the buried interface. More importantly, the perovskite quality is optimized and the buried interface defects are passivated due to the formation of coordination and hydrogen bondings. Benefiting from such a robust and efficient charge transfer configuration, a maximum power conversion efficiency of 14.58% is achieved in the optimized device, which represents the highest performance reported among those of low-temperature CsPbI2Br C-IPSCs. In addition, the unencapsulated device demonstrates better long-term and thermal stability.

Small Molecules Functionalized Zinc Oxide Interlayers for High Performance Low-Temperature Carbon-Based CsPbI2 Br Perovskite Solar Cells.

The charge recombination resulting from bulk defects and interfacial energy level mismatch hinders the improvement of the power conversion efficiency (PCE) and stability of carbon-based inorganic perovskite solar cells (C-IPSCs). Herein, a series of small molecules including ethylenediaminetetraacetic acid (EDTA) and its derivatives (EDTA-Na and EDTA-K) are studied to functionalize the zinc oxide (ZnO) interlayers at the SnO2 /CsPbI2 Br buried interface to boost the photovoltaic performance of low-temperature C-IPSCs. This strategy can simultaneously passivate defects in ZnO and perovskite films, adjust interfacial energy level alignment, and release interfacial tensile stress, thereby improving interfacial contact, inhibiting ion migration, alleviating charge recombination, and promoting electron transport. As a result, a maximum PCE of 13.94% with a negligible hysteresis effect is obtained, which is one of the best results reported for low-temperature CsPbI2 Br C-IPSCs so far. Moreover, the optimized devices without encapsulation demonstrate greatly improved operational stability.

Alkali Metal Cations Modulate the Energy Level of SnO2 via Micro-agglomerating and Anchoring for Perovskite Solar Cells.

N-type tin oxide (SnO2) films are commonly used as an electron transport layer (ETL) in perovskite solar cells (PSCs). However, SnO2 films are of poor quality due to facile agglomeration under a low-temperature preparation method. In addition, energy level mismatch between the SnO2 and perovskite (PVK) layer as well as interfacial charge recombination would cause open-circuit voltage loss. In this work, alkali metal oxalates (M-Oxalate, M = Li, Na, and K) are doped into the SnO2 precursor to solve these problems. First, it is found that the hydrolyzed alkali metal cations tend to change colloid size distribution of SnO2, in which Na-Oxalate with suitable basicity leads to most uniform colloid size distribution and high-quality SnO2-Na films. Second, the electron conductivity is enhanced by slightly agglomerated SnO2-Na, which facilitates the transmission of electrons. Third, alkali metal cations increase the conduction band level of SnO2 in the sequence of K+, Na+, and Li+ to promote band alignment between ETLs and perovskite. Based on the optimized film quality and energy states of SnO2-Na, the best PSC efficiency of 20.78% is achieved with a significantly enhanced open-circuit voltage of 1.10 V. This work highlights the function of alkali metal salts on the colloid particle distribution and energy level modulation of SnO2.

2D-MA3 Sb2 I9 Back Surface Field for Efficient and Stable Perovskite Solar Cells.

In perovskite solar cells (PSCs), a defective perovskite (PVK) surface and cliff-like energy offset at the interface always slow down the charge extraction; meanwhile, interface ion diffusion causes oxidation of the metal electrode, inducing device instability. Here, the in situ grown 2D-(CH3 NH2 )3 Sb2 I9 (MA3 Sb2 I9 ) on the back surface of MAPbI3 results in a more robust interface. MA3 Sb2 I9 changes the MAPbI3 surface to p-type and thus acts like a back surface field to drive charge extraction and suppress recombination, resulting in an obviously higher fill factor (FF) = 0.8 and power conversion efficiency (PCE) = 20.4% of SnO2 /MAPbI3 /MA3 Sb2 I9 /Spiro-OMeTAD (2,2',7,7'-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene) PSC than the pure MAPbI3 device. More importantly, strong chemical bonding of SbI prohibits ion diffusion, largely enhancing the thermal stability and longtime stability. Here, special 2D-MA3 Sb2 I9 constructs' robust band alignment and chemical environment at the interface are highlighted for efficient and stable PSCs.

Reconstruction of the (EMIm)xMA1-xPb[(BF4)xI1-x]3 Interlayer for Efficient and Stable Perovskite Solar Cells.

Defective grain boundaries (GBs) and surface trap states are detrimental to the efficiency and stability of perovskite solar cells (PSCs). In this research, ionic liquid (IL) is used to control the defect states at the perovskite surface and GBs. The newly formed (EMIm)xMA1-xPb[(BF4)xI1-x]3 interlayer promotes secondary grain growth to diminish GBs; besides, EMIM+ and BF4- fill the vacancies of MA+ and I- and also passivate undercoordinated Pb2+ trap states. The newly formed interface largely reduces the nonradiative recombination, thus enhancing the solar-cell performance to 19.0% (AM 1.5, 1 sun) with higher photovoltage and fill factor than the control device. Due to the hydrophobicity of the (EMIm)xMA1-xPb[(BF4)xI1-x]3 interlayer, the unencapsulated device stability in 30 days is much better than the control device under relative humidity (RH) = 20%. This work highlights IL-induced secondary grain growth and a defect passivation method for efficient and stable PSCs.