Interfacial versus Bulk Properties of Hole-Transporting Materials for Perovskite Solar Cells: Isomeric Triphenylamine-Based Enamines versus Spiro-OMeTAD

Abstract

Here, we report on three new triphenylamine-based enamines synthesized by condensation of an appropriate primary amine with 2,2-diphenylacetaldehyde and characterized by experimental techniques and density functional theory (DFT) computations. Experimental results allow highlighting attractive properties including solid-state ionization potential in the range of 5.33–5.69 eV in solid-state and hole mobilities exceeding 10 –3 cm 2 /V·s, which are higher than those in spiro-OMeTAD at the same electric fields. DFT-based analysis points to the presence of several conformers close in energy at room temperature. The newly synthesized hole-transporting materials (HTMs) were used in perovskite solar cells and exhibited performances comparable to that of spiro-OMeTAD. The device containing one newly synthesized hole-transporting enamine was characterized by a power conversion efficiency of 18.4%. Our analysis indicates that the perovskite–HTM interface dominates the properties of perovskite solar cells. PL measurements indicate smaller efficiency for perovskite-to-new HTM hole transfer as compared to spiro-OMeTAD. Nevertheless, the comparable power conversion efficiencies and simple synthesis of the new compounds make them attractive candidates for utilization in perovskite solar cells.

Electronic structure and interfacial features of triphenylamine- and phenothiazine-based hole transport materials for methylammonium lead iodide perovskite solar cells

“…the energy required to reorganize nuclei positions on a given oxidation state. The smaller the λ , the faster could be the hole transport, 37–39 indeed, the charge hopping rate ( k ) in our case can be defined by Marcus theory 40 as follows:where h is the Planck's constant, V is the electronic coupling between adjacent molecules in the structure, λ is the reorganization energy, k B is the Boltzmann constant and T is the temperature. The reported hopping rate is a special case of the more general Marcus formula that stands for the self-exchange reaction involving an electron exchange between two adjacent HTM molecules in which the free Gibbs energy change of the reaction is null.…”

“…the energy required to reorganize nuclei positions on a given oxidation state. The smaller the l, the faster could be the hole transport, [37][38][39] indeed, the charge hopping rate (k) in our case can be defined by Marcus theory 40 as follows:…”

Enhancement of Hole Extraction Efficiency of Dibenzothiophenes by Substitution Engineering: Toward Additive‐Free Perovskite Solar Cells with Power Conversion Efficiency Exceeding 20%

“…The best HTM hole mobility was observed for DBT1-based PSC, exhibiting much lower PCE (8.99%) as compared to DBT3-containing device (20.9%) despite the lower hole mobility of the latter one by roughly 4-5 times. This dichotomy is now a frequent observation, [31,51] pointing to the dominant importance of the perovskite-HTM and HTM-electrode interface properties in contrast to the hole-transport in the HTM layer. It is worth highlighting that, in the presence of the 2D PS layer, the hole extraction (transfer) of PS!HTM requires efficient HTM-PEABr interactions and couplings.…”

Catalytic Stereoselective Multicomponent Reactions for the Synthesis of Spiro Derivatives: Recent Progress

“…Enantioenriched spiro derivatives [12] are characterized by the interesting fusion of two molecular rings linked by a common tetrasubstituted stereogenic center. They are an important component of several natural products, [13–15] bioactive compounds, [16–20] and find applications in asymmetric catalysis, [21–24] thermally stable OLED, [25–31] sensing, [32–36] and HMT (hole‐transporting material) [37–46] . Compared with singly condensed heterocycles spiro‐hetero/carbocycles have the obvious advantage of structural compactness, which reduces lipophilicity [47] .…”