Xinxing Yin

Side-chain Engineering of Benzo[1,2-b:4,5-b']dithiophene Core-structured Small Molecules for High-Performance Organic Solar Cells.

Three novel small molecules have been developed by side-chain engineering on benzo[1,2-b:4,5-b’]dithiophene (BDT) core. The typical acceptor-donor-acceptor (A-D-A) structure is adopted with 4,8-functionalized BDT moieties as core, dioctylterthiophene as π bridge and 3-ethylrhodanine as electron-withdrawing end group. Side-chain engineering on BDT core exhibits small but measurable effect on the optoelectronic properties of small molecules. Theoretical simulation and X-ray diffraction study reveal the subtle tuning of interchain distance between conjugated backbones has large effect on the charge transport and thus the photovoltaic performance of these molecules. Bulk-heterojunction solar cells fabricated with a configuration of ITO/PEDOT:PSS/SM:PC71BM/PFN/Al exhibit a highest power conversion efficiency (PCE) of 6.99% after solvent vapor annealing.

Side-chain manipulation on accepting units of two-dimensional benzo[1,2-b:4,5-b′]dithiophene polymers for organic photovoltaics

Two donor–acceptor alternating polymers of bis(octylthio)thienyl benzo[1,2-b:4,5-b′]dithiophene (BDTTs) and fluorinated benzo[c][1,2,5]thiadiazole (fBT) or 5-dodecylthienyl-6-fluorobenzo[c][1,2,5]thiadiazole were designed for organic photovoltaic applications. The polymers displayed strong absorptions in the range of 300–650 nm and bandgaps of ∼1.60 eV. Bulk-heterojunction solar cells of PBDTTs-fBT and (6,6)-phenyl C71-butyric acid methyl ester (PC71BM) blends exhibited a maximum power conversion efficiency of 6.27%. Experimental results and theoretical modelling were correlated to reveal the impact of substitution on fluorinated BT on the optoelectronic properties of the resulting polymers.

Cost-effective hole transporting material for stable and efficient perovskite solar cells with fill factors up to 82%

A new small molecule-based hole selective material (HSM), 4,4′,4′′-(7,7′,7′′-(5,5,10,10,15,15-hexahexyl-10,15-dihydro-5H-diindeno[1,2-a:1′,2′-c]fluorene-2,7,12-triyl)tris(2,3-dihydrothieno[3,4-b][1,4]dioxine-7,5-diyl))tris(N,N-bis(4-methoxyphenyl)aniline) (TRUX-E-T), has been developed by a facile synthesis with reduced cost. The highest occupied molecular orbital energy level and lowest unoccupied molecular orbital energy level of TRUX-E-T are −5.10 and −2.50 eV, respectively, making it a suitable HSM for lead iodide perovskite solar cells. TRUX-E-T can be smoothly deposited onto perovskite layers, enabling efficient perovskite solar cells with thin TRUX-E-T layers (∼50 nm), which helps cut the unit cost of the HSL used in PVSCs to approximately one-fortieth (1/40) of 2,2′,7,7′-tetrakis (N,N-di-p-methoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD). Additionally, TRUX-E-T exhibits hole mobilities as high as 2.47 × 10−4 cm2 V−1 s−1, better than spiro-OMeTAD. As a result, our perovskite solar cells using TRUX-E-T have shown high fill factors up to 82%. The champion cell achieved a maximum power conversion efficiency of 18.35% (16.44%) when measured under reverse (forward) voltage scan under AM1.5 G 100 mW cm−2 illumination. Our un-encapsulated cells exhibited good stability in ambient air, maintaining 96.4% of their initial efficiency of 18.35% after 20 days of storage.