Design of single-porphyrin donors toward high open-circuit voltage for organic solar cells via an energy level gradient-distribution screening strategy of fragments: a theoretical study

A unified evaluation descriptor for π-bridges applied to metalloporphyrin derivatives

Establishing the structure of porphyrins with a A-π-D-π-A configuration is one of the effective strategies to maintain their dominance and compensate shortcomings through flexible changes in fragments. In this regard, π-bridges have attracted wide attention as a parameter affecting molecular backbones, electron transfer, energy levels, absorption, and other properties. However, the essence and influence of π-bridges have not yet been confirmed. In order to satisfy the requirements of intelligent application in molecular design, this study aimed to investigate the control effect of differences in π-bridge composition (thiophene and selenophene) and connection type (single bonds, ethylenic bonds and fused) on photoelectric performance. Y6 and PC61BM were used as acceptors to build donor/acceptor (D/A) interfaces and characterize the film morphology in three dimensions. Results showed that the essence of π-bridges involves a strong bridging effect (adjusting ability) between A and D fragments rather than highlighting its own nature. The large value could obtain high open circuit voltages (VOC), large separation and small recombination rates as well as stable and tight morphology. Therefore, adjusting ability is a unified descriptor for evaluating π-bridges, and it is an effective strategy to adjust material properties and morphology. This insight and discovery may provide a new evaluation descriptor for the screening and design of π-bridges.

A computational investigation about the effect of metal substitutions on the electronic spectra of porphyrin donors in the visible and near infrared regions

Porphyrin compounds have unique advantages because of their wide absorption range (about 300-1000 nm) and good planarity. At present, the effects of metal substitutions of porphyrin compounds on their photovoltaic properties are still not clear. In this paper, we have systematically modelled a series of porphyrin donors MP-TBO (M = 2H, Mg, Cu, Fe, Co, Zn and Ni), in which ZnP-TBO has been experimentally synthesized and the power conversation efficiency of organic solar cell based on it is up to 12.08 %. The photovoltaic properties of these MP-TBO molecules have been investigated via density functional theory (DFT) and time-dependent DFT. We find that CoP-TBO and NiP-TBO both have worse planarity and smaller dipole moments than other compounds. The electronic absorption spectra of these porphyrin donors all show three main absorption peaks. However, metal substitutions blue-shift the wavelength of absorption peaks and lower total absorption strength in the visible and near-infrared regions. Finally, we find that MgP-TBO and H₂P-TBO seem to be potential donors because both have more red-shifted wavelength of absorption peaks and higher absorption strength than other metal substitutions.

Theoretical design and characterization of new terpolymer donors based on PTB7Ir for high-efficiency triplet-material-based organic photovoltaics

In the current work, eleven terpolymer donors with different electron-withdrawing groups were designed and investigated based on the reported PTB7Ir to screen outstanding donors for triplet-material-based organic photovoltaics (T-OPVs). Geometry structures, frontier molecular orbital energy levels, energy driving forces (ΔE_L–L), absorption spectra, energy differences between S₁ and T₁ states (ΔE_ST), and driving forces of the triplet charge recombination (−ΔG_CRT) of PTB7Ir and designed 1–11 systems were evaluated by DFT and TD-DFT methods to estimate the light absorption abilities and the charge transfer dynamics. The results show that designed 5, 8, 10 and 11 possess larger spin–orbit couplings (SOC) affinity and smaller ΔE_ST and −ΔG_CRT values, which could effectively suppress the triplet charge recombination process at the donor/acceptor interface. Excitingly, the designed terpolymer 10 presents enhanced light absorption, revealing that it will be a promising donor candidate for high-performance T-OPV devices. Moreover, the results can provide theoretical guidelines to predict new terpolymer donors of T-OPVs.

Compared with PTB7Ir, the designed terpolymer 10 will be a promising donor candidate for high-performance T-OPVs.

Reducing Energy Loss in Organic Solar Cells by Changing the Central Metal in Metalloporphyrins

The effect of central donor core on the properties of A-π-D-π-A donors, where D is a porphyrin macrocycle, cyclopenta[2,1-b:3,4-b']dithiophene is the π bridge, and A is a dicyanorhodanine terminal unit, was investigated for the fabrication of the organic solar cells (OSCs), along [6,6]-phenyl-C71-butyric acid methyl ester (PC₇₁ BM) as electron acceptor. A new molecule consisting of Ni-porphyrin central donor core (VC9) showed deep HOMO energy level and OSCs based on optimized VC9:PC₇₁ BM realized overall power conversion efficiency (PCE) of 10.66 % [short-circuit current density (J_SC )=15.48 mA/cm² , fill factor (FF)=0.65] with high open circuit voltage (V_OC ) of 1.06 V and very low energy loss of 0.49 eV, whereas the Zn-porphyrin analogue VC8:PC₇₁ BM showed PCE of 9.69 % with V_OC of 0.89 V, J_SC of 16.25 mA/cm² and FF of 0.67. Although the OSCs based on VC8 showed higher J_SC in comparison to VC9, originating from the broader absorption profile of VC8 that led to more exciton generation, the higher value of PCE of VC9 is owing to the higher V_OC and reduced energy loss.