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Perovskite solar cells (PSCs) with superior performance have been recognized as a potential candidate in photovoltaic technologies. However, the defects in active perovskite layer induce non-radiative recombination which restricts the performance and stability of the PSCs. The construction of thiophene-based 2D structure is one of the significant approaches for surface passivation of hybrid PSCs that may combine the benefits of the stability of 2D perovskite with the high performance of 3D perovskite. Here, a sulfur-rich spacer cation 2-thiopheneethylamine iodide (TEAI) is synthesized as a passivation agent for the construction of three-dimensional/two-dimensional (3D/2D) perovskite bilayer structure. TEAI-treated PSCs possess a much higher efficiency (20.06%) compared to the 3D perovskite (MAFAPbI3) devices (17.42%). Time-resolved photoluminescence (TRPL) and femtosecond transient absorption (TA) spectroscopy are employed to investigate the effect of surface passivation on the charge carrier dynamics of the 3D perovskite. Additionally, the stability test of TEAI-treated perovskite devices reveals significant improvement in humid (RH ~ 56%) and thermal stability as the sulfur-based 2D (TEA)2PbI4 material self-assembles on the 3D surface making the perovskite surface hydrophobic. Our findings provide a reliable approach to improve device stability and performance successively, paving the way for industrialization of PSCs.

This review covers the recent experimental development on spin alignment measurements of $K^{*0}$ and $\phi$ vector mesons in heavy-ion and pp collisions at RHIC and LHC energies. Measurements in $e^+e^-$ collisions at LEP energies are also discussed. Spin alignment of vector mesons are studied by measuring the second diagonal element $\rho_{00}$ of spin density matrix. The $\rho_{00}$ is obtained by measuring the angular distribution of vector meson decay daughter with respect to the quantization axis in vector meson rest frame. Measured $\rho_{00}$ values for vector mesons are found to be larger than 1/3 at high momentum in $e^+e^-$ collisions at LEP energies, suggesting the preferential production of vector meson with helicity zero state from the fragmentation process. The $\rho_{00}$ values are found to be smaller than 1/3 ($\rho_{00}$ = 1/3 implies no spin alignment) for $K^{*0}$ and $\phi$ vector mesons at low transverse momentum in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV. This observations are qualitatively consistent with the expectation from models which attribute the spin alignment effect due to polarization of quarks in the presence of large initial angular momentum in non-central heavy-ion collisions and its subsequent hadronization by the process of recombination. No significant spin alignment effect is observed for $K^0_S$ (spin = 0) in mid-central Pb--Pb collisions and for vector mesons in pp collisions. However, the preliminary results of $\rho_{00}$ for $\phi$ mesons are larger than 1/3 at intermediate $p_{\mathrm{T}}$ in Au--Au collisions at RHIC energies and can be attributed to the presence of $\phi$ meson field. Although there is evidence of spin alignment effect of vector mesons in heavy-ion collisions but the measured effect is surprisingly larger in context of hyperon polarization. Therefore these results will trigger further theoretical study., Comment: 25 pages, 13 figures

The data on transverse momentum integrated hadron yields in different multiplicity classes of p+p collisions at $\sqrt{s}=7$ TeV have been analyzed to extract the chemical freeze-out parameters using a thermal model. The chemical freeze-out parameters have been extracted for three different freeze-out schemes: i. unified freeze-out for all hadrons in complete thermal equilibrium (1CFO), ii. unified freeze-out for all hadrons with an additional parameter $\gamma_S$ which accounts for possible out-of-equilibrium production of strange hadrons (1CFO$+\gamma_S$), and iii. separate freeze-out for hadrons with and without strangeness content (2CFO). It has been observed that 1CFO$+\gamma_S$ scheme gives the best description of the hadronic yields at midrapidity when multiplicity ($\langle dN_{ch}/d\eta \rangle$) of the collision is less than 10. This indicates that the strangeness is out of equilibrium in most of the multiplicity classes of p+p collisions. All the three parameters of this CFO scheme, temperature ($T$), radius of the fireball ($R$) and strangeness suppression factor ($\gamma_S$) increase with the increase of $\langle dN_{ch}/d\eta \rangle$. Further, we have compared applicability of different CFO schemes considering two more colliding system p+Pb at $\sNN$ = 5.02 and Pb+Pb at $\sNN$ = 2.76 TeV along with p+p collisions at $\sqrt{s}=7$ TeV. We observe a freeze-out volume (or multiplicity) dependence of CFO schemes regardless of colliding ions. The 1CFO+$\gamma_S$, 1CFO and 2CFO schemes provide best description of the data when the dimension less quantity $VT^3$ approximately satisfies the conditions $VT^3 <50$, $50 < VT^3 < 100$ and $VT^3 > 100$ respectively or the corresponding multiplicity satisfies the conditions $\langle dN_{ch}/d\eta \rangle<30$, $30 < dN_{ch}/d\eta < 60$ and $\langle dN_{ch}/d\eta \rangle>100$ respectively., Comment: 9 Pages, 6 figures