Lihui Jiang

High performance polymer solar cells based on a two dimensional conjugated polymer from alkylthienyl-substituted benzodifuran and benzothiadiazole

A new low bandgap D–A copolymer PBDFTDTBT containing 4,8-bis(2-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b;3,4-b′]difuran (BDFT) and 4,7-di(thiophen-2-yl)-5,6-dioctyloxybenzo[c][1,2,5]thiadiazole (DTBT) units was synthesized and characterized for application as a donor material in polymer solar cells (PSCs). The PBDFTDTBT film showed a broad absorption band from 300 nm to around 730 nm in the visible light region and the hole mobility of the blend of PBDFTDTBT and PC71BM reached up to 0.36 cm2 V−1 s−1 by using the space charge limited current (SCLC) method. The PSCs based on PBDFTDTBT:PC71BM (1 : 1.5, w/w) exhibited a promising power conversion efficiency (PCE) of 6.0% under the illumination of AM 1.5 G, 100 mW cm−2 with a high short circuit current density (Jsc) of 12.04 mA cm−2 and an open circuit voltage (Voc) of 0.76 V.

Effect of fluorination on the performance of poly(thieno[2,3-f]benzofuran-co-benzothiadiazole) derivatives

In order to shed light on the effects of different numbers of fluorine atoms in donor–acceptor (D–A) conjugated polymers on the photophysics and photovoltaic properties, three polymers named PTBFBT-0F, PTBFBT-1F, PTBFBT-2F were synthesized and thoroughly investigated. The nonfluorinated benzothiadiazole (BT) polymer (PTBFBT-0F) has a highest occupied molecular orbital (HOMO) energy level of −4.98 eV and a low bandgap of 1.64 eV. When one of the hydrogen atoms of the BT unit was substituted by a fluorine atom (PTBFBT-1F), a small blue-shift in UV-Vis absorption and a lower HOMO energy level of −5.11 eV were observed, thus a similar Voc and Jsc were obtained. Nevertheless, the FF of PTBFBT-2F was further improved from 46% to 53% due to the relatively higher and balanced electron/hole charge transport mobility of 1.83 × 10−5 cm2 V−1 s−1 and 1.52 × 10−5 cm2 V−1 s−1. Using a Ca/Al top electrode, devices based on PTBFBT-0F, PTBFBT-1F, PTBFBT-2F as electron donor showed increasing power conversion efficiencies (PCE) of 3.0%, 3.6% and 4.2%, respectively. Furthermore, replacing Ca with a zirconium acetylacetonate film (ZrAcac) as the cathode buffer layer (CBL), a PCE of 5% with PTBFBT-2F as the donor was obtained.

Side-chain fluorination on the pyrido[3,4-b]pyrazine unit towards efficient photovoltaic polymers

A series of new polymer donors (PT-PP, PT-2fPP and PT-4fPP) were synthesized based on alkylthiophene substituted benzodithiophene (BDT-T) and pyrido[3,4-b]pyrazine (PP) building blocks and the effects of fluorination on the polymer properties were explored. Photophysical properties, charge mobilities and morphologies of the three polymers have been intensively investigated. The results indicated that the introduction of the fluorine atom at meta-positions of phenyl substituted PP unit hardly affected their highest occupied molecular orbital (HOMO) level. More importantly, controlling the degree of side-chain fluorination in the polymers is crucial for optimizing the blend morphology. Three polymers showed different photovoltaic properties. The polymer solar cell (PSC) based on the single layer device structure of ITO/PEDOT:PSS/PT-4fPP:PC71BM (1:1, w:w)/ZrAcac/Al demonstrates a high power conversion efficiency (PCE) of 7.61% under the illumination of AM 1.5G, 100 mW cm−2, which is the highest value for PP-based PSCs.

A new fluoropyrido[3,4-b]pyrazine based polymer for efficient photovoltaics

In order to improve the photovoltaic performance of pyrido[3,4-b]pyrazine (PP)-based polymers, a new fluoropyrido[3,4-b]pyrazine based D–A type polymer (BDT-S-fPP) was synthesized. The optical, electrochemical and photovoltaic properties were well investigated. A power conversion efficiency (PCE) over 6.0% with a single junction device was obtained, which is the highest PCE among the PP-based polymers reported to date.

(B,N)-Doped 3D porous graphene–CNTs synthesized by chemical vapor deposition as a bi-functional catalyst for ORR and HER

Novel (B,N)-doped three-dimensional (3D) porous graphene–carbon nanotubes (CNTs) can be used as an excellent alkaline and acid tolerant electrocatalyst for both the oxygen reduction reaction (ORR) and the hydrogen evolution reaction (HER). Based on density functional theory, the H and O atoms’ pre-and post-adsorption energy can effectively reduce the reaction energy barrier.