Origin of Sn(II) oxidation in tin halide perovskites

Tin-halide perovskites have great potential as photovoltaic materials, but their performance is hampered by undesirable oxidation of Sn(ii) to Sn(iv). NMR proves DMSO to be a main cause of oxidation

Photovoltaic potential of tin perovskites revealed through layer-by-layer investigation of optoelectronic and charge transport properties

Tin perovskites are the most promising environmentally friendly alternative to lead perovskites. Among tin perovskites, FASnI3 (CH4N2SnI3) shows optimum band gap, and easy processability. However, the performance of FASnI3 based solar cells is incomparable to lead perovskites for several reasons, including energy band mismatch between the perovskite absorber film and the charge transporting layers (CTLs) for both types of carriers, i.e., for electrons (ETLs) and holes (HTLs). However, the band diagrams in the literature are inconsistent, and the charge extraction dynamics are poorly understood. In this paper, we study the energy band positions of FASnI3 based perovskites using Kelvin probe (KP) and photoelectron yield spectroscopy (PYS) to provide a precise band diagram of the most used device stack. In addition, we analyze the defects within the current energetic landscape of tin perovskites. We uncover the role of bathocuproine (BCP) in enhancing the electron extraction at the fullerene C60/BCP interface. Furthermore, we used transient surface photovoltage (tr-SPV) for the first time for tin perovskites to understand the charge extraction dynamics of the most reported HTLs such as NiOx and PEDOT, and ETLs such as C60, ICBA, and PCBM. Finally, we used Hall effect, KP, and time-resolved photoluminescence (TRPL) to estimate an accurate value of the p-doping concentration in FASnI3 and showed a consistent result of 1.5 * 1017 cm-3. Our findings prove that the energetic system of tin halide perovskites is deformed and should be redesigned independently from lead perovskites to unlock the full potential of tin perovskites.Comment: 22 pages, 5 figure

Dipole-tunable interfacial engineering strategy for high-performance all-inorganic red quantum-dot light-emitting diodes

All-inorganic quantum dot (QD) light-emitting diodes (AI-QLEDs) with excellent stability received enormous interest in the past few years. Nevertheless, the vast energy offset and the high trap density at the NiOX/QDs interface limit hole injection leading to fluorescence quenching and hampering the performance. Here, we present self-assembled monolayers (SAMs) with phosphonic acid (PA) anchoring groups modifying NiOX hole transport layer (HTL) to tune energy level and passivate trap states. This strategy facilitates hole injection owning to the well-aligned energy level by interface dipole, downshifting the vacuum level, reducing the hole injection barrier from 0.94 eV to 0.28 eV. Meanwhile, it mitigates the interfacial recombination by passivating surface hydroxyl group (-OH) and oxygen vacancy (VO) traps in NiOX. The electron leakage from QDs toward NiOX HTL is significantly suppressed. The all-inorganic R-QLEDs exhibit one of the highest maximum luminance, external quantum efficiency and operational lifetime of 88980 cd m−2, 10.3% and 335045 h (T50@100 cd m−2), respectively. The as-proposed interface engineering provides an effective design principle for high-performance AI-QLEDs for future outdoor and optical projection-type display applications

Interfacial passivation engineering for highly efficient quantum dot light-emitting diodes via aromatic amine-functionalized dipole molecules

Blue quantum dot (QD) light-emitting diodes (QLEDs) exhibit unsatisfactory operational stability and electroluminescence (EL) properties due to severe nonradiative recombination induced by large numbers of dangling bond defects and charge imbalance in QD. Herein, dipolar aromatic amine-functionalized molecules with different molecular polarities are employed to regulate charge transport and passivate interfacial defects between QD and the electron transfer layer (ETL). The results show that the stronger the molecular polarity, especially with the −CF3 groups possessing a strong electron-withdrawing capacity, the more effective the defect passivation of S and Zn dangling bonds at the QD surface. Moreover, the dipole interlayer can effectively reduce electron injection into QD at high current density, enhancing charge balance and mitigating Joule heat. Finally, blue QLEDs exhibit a peak external quantum efficiency (EQE) of 21.02% with an operational lifetime (T50 at 100 cd m–2) exceeding 4000 h

Ionic Liquid Stabilizing High‐Efficiency Tin Halide Perovskite Solar Cells

Tin halide perovskites attract incremental attention to deliver lead-free perovskite solar cells. Nevertheless, disordered crystal growth and low defect formation energy, related to Sn(II) oxidation to Sn(IV), limit the efficiency and stability of solar cells. Engineering the processing from perovskite precursor solution preparation to film crystallization is crucial to tackle these issues and enable the full photovoltaic potential of tin halide perovskites. Herein, the ionic liquid n-butylammonium acetate (BAAc) is used to tune the tin coordination with specific O…Sn chelating bonds and NH…X hydrogen bonds. The coordination between BAAc and tin enables modulation of the crystallization of the perovskite in a thin film. The resulting BAAc-containing perovskite films are more compact and have a preferential crystal orientation. Moreover, a lower amount of Sn(IV) and related chemical defects are found for the BAAc-containing perovskites. Tin halide perovskite solar cells processed with BAAc show a power conversion efficiency of over 10%. This value is retained after storing the devices for over 1000 h in nitrogen. This work paves the way toward a more controlled tin-based perovskite crystallization for stable and efficient lead-free perovskite photovoltaics