Full inorganic perovskites display their poten tial to function as stable photovoltaic materials better than the hybrid organic-inorganic perovskites. However, to date, the cesium lead iodide perovskite, which displays a promising absorbance range, has suffered from low stability, which degrades to a nonactive photovoltaic phase rapidly. ln this work, we show that the black phase of cesium lead iodide can be stabilized when the perovskite dimensionality is reduced. X ray diffraction, absorbance, and scanning electron micros copy were used to follow the degradation process of various dimensionalities under room conditions and 1 sun illumina tion. When comparing the effect on the stability and Time) •••••••• photostability of cesium lead iodide with linear or aromatic barrier molecules, the aromatic barrier molecule displays better photostability for over 700 h without degradation under continuous 1 sun illumination than does the linear barrier molecule. Theoretical calculations show that the addition of the barrier molecule makes a different charge distribution over the perovskite structure, which stabilizes the CsPbl 3 black phase. This work provides the possibility to use the CsPbl 3 perovskite as a stable photovoltaic material in solar cells.

The selective contacts in perovskite solar cells play a major role in solar cell (SC) performance and optimization. Herein, the inverted architecture is focused on, where systematically the electron transport layer (ETL) and the hole transport layer (HTL) from the SC structure are eliminated. Three main architectures of the SCs are studied: a fully inverted structure, an ETL‐free structure, and a HTL‐free structure. Cathodoluminescence and photoluminescence are measured on various architectures, revealing the electron and hole injection efficiency from the perovskite to selective contacts. Moreover, surface voltage spectroscopy shows the type and the band‐edge transition of these layers. Finally, the photovoltaic (PV) performance of different SCs shows that eliminating the HTL is most critical for PV performance, compared with ETL‐free and fully inverted SC configurations. Current−voltage hysteresis curves prove that efficient selective contacts are essential to eliminate this phenomenon. Measuring the ideality factor shows that the dominant mechanism in ETL‐free SCs is surface recombination, whereas in the other cases, it is Shockley–Reed–Hall recombination. This work provides knowledge about the functionality of methylammonium lead iodide as an electron conductor and as a hole conductor.

In this work, 2D chiral perovskite is demonstrated, where the barrier molecules are the two enantiomers (R)‐(+)‐α‐Methylbenzylamine (R‐MBA) and (S)‐(‐)‐α‐Methylbenzylamine (S‐MBA). The chirality is manifested at high χ values and pure 2D structure measured by circular dichroism (CD) (where the perovskite general formula is ABX3 χ (S/R‐MBA)2PbI4, χ is the ratio of the barrier molecule to the small cation (A+)). The anisotropy factor (gabs) decreased by an order of magnitude when decreasing the χ value achieving 0.0062 for pure 2D. Ab initio many‐body perturbation theory successfully describes the bandgaps, absorbance, and CD measurements. For the first time, these quasi‐2D chiral perovskites are integrated into the solar cell. Using circular polarization (CP) and cutoff filter, the chirality effect from the solar cells photovoltaic response is able to be distinguished. It is revealed that at high χ values, the chirality affects the current density of the solar cell more than at low χ values while the open‐circuit voltage didn't change. These chiral 2D perovskite are new class of materials which open the way for polarized hybrid perovskite.

Hybrid metal halide perovskites have seen an exponential increase in the scientific community due to their successful introduction in solar cells. However these materials are known to suffer from thermal...