penghuang

The chemical structure of conjugated polymers plays an important role in determining their physical properties that, in turn, dictates their performance in photovoltaic devices. 5-Fluoro-2,1,3-benzothiadiazole, an asymmetric unit, is incorporated into a thiophene-based polymer backbone to generate a hole conducting polymers with controlled regioregularity. A high dipole moment is seen in regioregular polymers, which have a tighter interchain stacking that promotes the formation of a morphology in bulk heterojunction blends with improved power conversion efficiencies. Aliphatic side chain substitution is systematically varied to understand the influence of side chain length and symmetry on the morphology and resultant performance. This side chain modification is found to influence crystal orientation and the phase separated morphology. Using the asymmetric side chain substitution with regioregularity of the main chain, an optimized power conversion efficiency of 9.06% is achieved, with an open circuit voltage of 0.72 V, a short circuit current of 19.63 mA cm⁻², and a fill factor over 65%. These results demonstrate that the local chemical environment can dramatically influence the physical properties of the resultant material.

The unidirectional regioregular conjugated polymers using 5-fluoro-2,1,3-benzothiadiazole (FBT) asymmetric unit were synthesized. Compared with the regiorandom control polymers, the regioregular polymers with a unidirectional fluorine atom alignment can lead to a progressive dipole moment along the backbone. The regioregular FBT polymers exhibit tighter interchain stacking and better morphology in bulk heterojunction blends, giving rise to improved power conversion efficiency.

The large energy loss (>0.6 eV) in polymer solar cells (PSCs) is limiting the improvement of photovoltage. In article number 1600148, Xiaofeng Xu, Wei Ma, Ergang Wang, and co-workers report that a low band gap (1.49 eV) polymer attains a high photovoltage of 1.0 V with efficiency of 6.7% in PSCs. It represents an impressively low energy loss of 0.49 eV, which challenges the current paradigm and reveals the potential to further enhance the performance of PSCs.

In this work, different from the commonly explored strategy of incorporating a smaller cation, MA⁺ and Cs⁺ into FAPbI₃ lattice to improve efficiency and stability, it is revealed that the introduction of phenylethylammonium iodide (PEAI) into FAPbI₃ perovksite to form mixed cation FA_xPEA_1–xPbI₃ can effectively enhance both phase and ambient stability of FAPbI₃ as well as the resulting performance of the derived devices. From our experimental and theoretical calculation results, it is proposed that the larger PEA cation is capable of assembling on both the lattice surface and grain boundaries to form quais-3D perovskite structures. The surrounding of PEA⁺ ions at the crystal grain boundaries not only can serve as molecular locks to tighten FAPbI₃ domains but also passivate the surface defects to improve both phase and moisture stablity. Consequently, a high-performance (PCE:17.7%) and ambient stable FAPbI₃ solar cell could be developed.

The introduction of a bulkier phenylethylammonium cation into FAPbI₃ is revealed to effectively enhance both phase and ambient stability of FAPbI₃. The larger hydrophobic cation is proposed to assemble on lattice surface and grain boundaries to form quasi-3D perovskite structures, which tightens FAPbI₃ domains and passivates surface defects, leading to a efficient and stable FAPbI₃ based solar cell.

In this work we systematically investigated the role of reduced graphene oxide (rGO) in hybrid perovskite solar cells (PSCs). By mixing rGO within the mesoporous TiO₂ (m-TiO₂) matrix, highly efficient solar cells with power conversion efficiency values up to 19.54 % were realized. In addition, the boosted beneficial role of rGO with and without Li-treated m-TiO₂ is highlighted, improving transport and injection of photoexcited electrons. This combined system may pave the way for further development and optimization of electron transport and collection in high efficiency PSCs.

rGO for efficiency! The effect of incorporating reduced graphene oxide (rGO) within the electron-transport, active, and hole-transport layers of a perovskite solar cell is investigated. Incorporation of rGO into the mesoporous TiO₂ matrix results in highly efficient solar cells with power conversion efficiency of up to 19.54 %.