The electronic properties of MAGeI₃are comparable to MAPbI₃, and it can act as a new lead-free perovskite candidate.

Perovskite solar cells (PSCs) with organic small molecules as hole transport materials (HTMs) have attracted considerable attention due to their power conversion efficiencies as high as 20%. In the present work, three new spiro-type hole transport materials with spiro-cores, i.e. Spiro-F1, Spiro-F2 and Spiro-F3, are investigated by using density functional theory combined with the Marcus theory and Einstein relation. Based on the calculated and experimental highest occupied molecular orbital (HOMO) levels of 30 reference molecules, an empirical equation, which can predict the HOMO levels of hole transport materials accurately, is proposed. Moreover, a simplified method, in which the hole transport pathways are simplified to be one-dimensional, is presented and adopted to qualitatively compare the molecular hole mobilities. The calculated results show that the perovskite solar cells with the new hole transport materials can have higher open-circuit voltages due to the lower HOMO levels of Spiro-F1 (−5.31 eV), Spiro-F2 (−5.42 eV) and Spiro-F3 (−5.10 eV) compared with that of Spiro-OMeTAD (−5.09 eV). Furthermore, the hole mobilities of Spiro-F1 (1.75 × 10⁻² cm² V⁻¹ s⁻¹) and Spiro-F3 (7.59 × 10⁻³ cm² V⁻¹ s⁻¹) are 3.1 and 1.4 times that of Spiro-OMeTAD (5.65 × 10⁻³ cm² V⁻¹ s⁻¹) respectively, due to small reorganization energies and large transfer integrals. Interestingly, the stability properties of Spiro-F1 and Spiro-F2 are shown to be comparable to that of Spiro-OMeTAD, and the dimers of Spiro-F2 and Spiro-F3 possess better stability than that of Spiro-OMeTAD. Taking into consideration the appropriate HOMO level, improved hole mobility and enhanced stability, Spiro-F1 and Spiro-F3 may become the most promising alternatives to Spiro-OMeTAD. The present work offers a new design strategy and reliable calculation methods towards the development of excellent organic small molecules as HTMs for highly efficient and stable PSCs.

The electronic structures, optical properties and hole mobilities of 4-(4-phenyl-4-α-naphthylbutadieny)-triphenylamine and its five derivatives are investigated by density functional theory (DFT). The results show that the highest occupied molecular orbital (HOMO) of all molecules is almost fully delocalized throughout the whole molecule, and the substituents –N(CH₃)₂ and –C₆H₅ denoted as molecules 6 and 2, respectively, have the largest contribution to the HOMO, which is favorable for hole transfer integral and hole mobility. Spectrum analysis indicates that all molecules have large Stokes shifts based on absorption and emission spectra. In addition, it is found that the hole reorganization energy of all molecules is about 0.5 times compared to that of electrons, which implies that hole mobility is bigger than electron mobility. On the basis of predicted packing motifs, the hole mobilities (u) of all molecules are also obtained. The largest hole mobility of molecule 2 (0.1063 cm² V⁻¹ s⁻¹) is found to be higher than that of other molecules due to the face-to-face stacking mode, which suggests that –C₆H₅ is a good substituent group for improving hole mobility compared to other electron releasing groups. We hope that our results will be helpful for the further rational molecular design and synthesis of novel hole transport materials (HTMs) for high performance perovskite-type solar cells.

MAGe _0.75 Pb _0.25 I ₃ with the highest theoretical efficiency of 24.24% is superior to MAPbI ₃ , which can become the best candidate.

Highly oxidized multifunctional organic molecules, which span a wide range of low volatilities, are capable of driving particle formation as well as the initial growth of particles in the atmosphere. However, their participant mechanism in new particle formation still remains largely ambiguous. Here we present an investigation of the potentially participant mechanism of the simplest hydroxyl acid, glycolic acid (GA) on clusters formation by sulfuric acid (SA) and ammonia (A). Density functional theory calculations at the M062X/6-311++G(3df,3pd) level of theory combining with atmospheric cluster dynamics code simulations of ${(\text{????????})}_x\cdot {\text{????}}_y\cdot {(\text{????????})}_z$ cluster ($\text{y}\le \text{x}$ + z ≤ 3) systems at different temperatures (298, 278, 258, 238, and 218 K) give direct evidence of the enhancement effect of GA on the formation rates of SA-A-based clusters at high concentration of GA and T = 238 K and 218 K. Moreover, within GA’s enhancement concentrations, the enhancement strength R of GA presents a positive dependence on its atmospheric concentrations and a negative dependence on temperature. A competitive relationship between SA and GA has been identified through the negative dependence of R on the concentrations of SA. The influence of A on R is more complex that R first increases, reaching a maximum value, and then decreases with the increasing concentration of A. Finally, the combination of the traced growth paths of the system with the enhancement strength of GA suggests a “catalytic” enhancement mechanism of GA where GA acts as a mediate bridge for the formation of pure SA-A-based clusters.