In this report, a pivotal improvement in the performance of dye‐sensitized solar cells has been achieved, thus taking it one step closer toward the commercialization. Through the stepwise modification on the anthracene‐based organic sensitizers, the alteration of alkyl to alkoxy chain and incorporation of electron deficient moieties in the new sensitizing dyes TY3, TY4, and TY6 are found to play a significant role in the efficiency enhancement. The dye TY6, when tested under 1 sun (AM 1.5G) illumination, is found to exhibit the best efficiency of 8.08% in the series reported here. Taking it further, sensitizer TY6 achieves a milestone by displaying an efficiency of 28.56% when tested under T5 fluorescent illumination of 6000 lux and 20.72% under same illuminance from a commercial light emitting diode light source. Such an excellent performance can be attributed to its outstanding J SC and V OC, which are characteristic properties of these anthracene dyes.

A new series of N-heterocyclic carbene (NHC)-pyridine ruthenium complexes incorporating a carbene unit as an ancillary ligand were designed and successfully synthesized by using simple synthetic methods. The photophysical, electrochemical and photovoltaic properties of these NHC-pyridine based ruthenium complexes were investigated. These complexes showed photoelectric conversion efficiencies in the range of 6.43 ∼ 7.24% under the illumination of AM 1.5 (100 mW cm(-2)). Interestingly, the modifications on the ancillary ligand of these sensitizers by removal of an alkoxyl group and replacement of the octyl chain with a 3,5-difluorobenzyl group showed a 13% increase in the conversion efficiency for the CifPR dye. These results demonstrated that structural modifications on the NHC-pyridine ancillary ligand of ruthenium complexes results in dye-sensitized solar cells exhibiting a comparable cell performance to that obtained using the standard N719 dye.

Dye-sensitized solar cells (DSSCs) are being investigated extensively for their use in renewable energy technologies because of their low cost and high light-to-electrical energy conversion efficiency.[1] Since their initial report in 1991 by ORegan and Grätzel, DSSCs have attracted much attention from researchers, resulting in the preparation of thousands of ruthenium polypyridine complexes, non-ruthenium organometallic dyes, and metal-free organic sensitizers. [2,3] Organic dyes exhibiting high molar absorption coefficients and presenting a variety of specific functional groups, allowing fine tuning of the absorption spectra, have provided respectable incident photon-to-current conversion efficiencies (IPCEs).[2] Coordination complexes of ruthenium, including N3, [4,5] N719, [6,7] and black dyes, [8][9][10] have also received significant attention because their photophysical and photochemical properties provide DSSCs with excellent photoelectric conversion efficiencies. The most common inorganic dyes exploited in DSSCs are typically ruthenium(II) polypyridine complexes.[3] Several attempts have been made to enhance the efficiency and long-term stability of the dyes, including increasing the conjugation length of the anchoring or ancillary ligand using thiophene, [11,12] carbazole, [13] or other [14][15][16][17] substituents. Long-term stability can be achieved by modifying the architecture of amphiphilic bis(bipyridyl) Ru II dyes featuring alkyl, [18][19][20] alkoxy, [16] or other [21] substituent groups. Grätzel and co-workers replaced the NCS ligand of a ruthenium polypyridine complex with an anionic carbon atom as an alternative approach to structural modification. [22,23] Herein, we report a set of N-heterocyclic carbene (NHC)/pyridine ruthenium complexes, in which one of the nitrogen atoms in the traditional bipyridine framework has been replaced by a carbon atom, for use in DSSCs exhibiting enhanced solar cell performance.Although there is much research on the preparation of metal-carbene complexes and their roles as catalytic reagents and luminescent emitters, their photovoltaic characteristics remain relatively unknown. NHC-pyridine-based ligands, with their unique set of electronic properties, are an exceptional class of donors; therefore, we expected them to make excellent ancillary ligands. The essential requirement of a dye that provides a DSSC with high efficiency is for the energy level of the lowest unoccupied molecular orbital (LUMO) of the sensitizer to be sufficiently high for efficient charge injection into the TiO 2 electrode, while the energy level of the highest occupied molecular orbital (HOMO) must be sufficiently low for efficient regeneration of the oxidized dye by the hole-transport material. Several methods have been reported to lower the HOMO energy level through tuning of the ancillary ligands and their substituents. [3,11,13] The use of ruthenium complexes bearing ancillary ligands functionalized with NHC-pyridine units might be an alternative approach toward tuning the frontier o...

Interfaces play a decisive role in perovskite solar cells’ power conversion efficiency and their long‐term durability. Small‐molecule hole‐transporting materials (HTMs) have grabbed enormous attention due to their structural flexibility, material properties, and stabilities, allowing for improved operational durability in perovskite photovoltaics. This study synthesizes and investigates a new class of benzimidazole‐based small molecules, named YJS001 and YJS003, serving as the HTMs to enable high‐efficiency mixed‐cation mixed‐halide perovskite solar cells. The benzimidazole‐based materials are dopant‐free HTMs composed of donor and acceptor building blocks that are designed to engineer the energy level alignment near the HTM/perovskite interface. Mixed‐cation mixed‐halide perovskites can be grown uniformly on both HTMs with large crystalline grains. It is discovered that the donor‐rich YJS003‐based solar cell exhibits a high open‐circuit voltage of 1.09 V with a champion power conversion efficiency of over 20%. Power‐dependent current–voltage characteristics of the solar cells are analyzed, from which the high performance of YJS003's excellent hole mobility and well‐aligned energy level is attributed. This work introduces a new class of benzimidazole‐based small molecules as HTMs, that paves the path for dopant free interface material development for commercialization of perovskite solar cells.

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