Designing adamantane-based HTMs for perovskite solar cells and utilizing electrostatic potential maps to evaluate the hole mobility.

Experimental and theoretical HOMO energy correlation of tetraphenylbenzidine (TPB)-based hole transport materials (HTMs) was successfully achieved through adiabatic ground-state oxidation potential calculation using LC-ωPBE. Similarly, trends in the computed excitation energies and hole reorganization energies of the HTMs are in agreement with the experimental band gaps and hole mobilities, respectively. Using these established correlations, the calculated properties of novel TPB-based HTMs were analyzed, and among the derivatives, TPB with attached fluorene (Fl) has less absorption in the visible region, a lower hole reorganization energy, and a deeper HOMO level compared to the reference. These properties signify that Fl could be a promising HTM in perovskite solar cells because this material will not compete with the perovskite absorption, will be efficient for hole transport due to its better hole mobility, and will eventually enhance the open-circuit voltage of the device. All of these factors could improve the efficiency of the perovskite solar cell.

This paper reports new D-D-π-A dyes based on N-annulated perylene, emphasizing the enhanced dye-to-semiconductor charge-transfer mechanism. A series of DFT calculations for new tPA-perylene-based dyes was conducted, starting from the systematic selection of DFT methods by reproducing the experimentally obtained properties of known perylene-based sensitizers. Accordingly, using the LC-ωPBE xc functional with 6-31+G(d) basis set for the time-dependent calculations of the excitation energies, a damping parameter of ω = 0.150 Bohr was found to be most appropriate for dyes having spatial orbital overlap value of 0.21 ≤ Λ ≤ 0.38, while ω = 0.175 Bohr is suitable for analogues with 0.43 ≤ Λ ≤ 0.57. Moreover, the mPWHandHPW91/6-31G(d) method gave high accuracy in GSOP calculations. The comparison between the properties of tPA-based donor groups has revealed that the semirigid tPA-based D4 unit is an effective donor group for perylene-based dye. Initial screening of the acceptor designs resulted in PLz4 dye with promising charge-transfer mechanism and highly favorable dye-TiO interaction based on the calculated dipole moment of the dye and dye-TiO complex. The attachment of the substituted-hydroacridine donor unit (D4) to PLz4 afforded a bathochromically shifted absorbance and improved molar absorptivity signifying its effective electron-donating ability. Among the D-D-π-A dyes, DP46 is expected to render a relatively high V and J supported by the calculated optical properties, oxidation potentials, ionization potential, and electron affinity values.

Bacteriochlorin-based dyes, having a push-pull type of configuration similar to that of the YD2 dye, were theoretically designed based on modification of the macrocycle and π-conjugated bridge for use in dye-sensitized solar cells. Various parameters were assessed to determine its structure-property relationships, such as the absorption profile based on time-dependent density functional theory, nonlinear optical properties from (hyper)polarizability data, ground- and excited-state oxidation potentials, and the electronic properties of the free and adsorbed dyes. On the basis of the results, the most appropriate macrocycle would be 7,7,17,17-tetramethyl-7H,8H,17H,18H-porphyrin and, for its π-conjugated bridge, either thieno[3,2-b]thiophene, dithieno[3,2-b:2',3'-d]thiophene, or 4,4-diisopropyl-4H-cyclopenta[2,1-b:3,4-b']dithiophene. These newly designed dyes produced an absorption spectra having a range of 300-800 nm, which could likely increase the light harvesting efficiency. It has better nonlinear properties than the reference, thereby ensuring higher charge-transfer properties. Also, the dye regeneration efficiency is within the optimized value of 0.2 eV, which could minimize the excessive loss of voltage. This shows that through theoretical approach we can deductively design analogues before synthesis to streamline the process in the design of dyes to produce efficient dye-sensitized solar cells.