•A four-armed TPA-based molecule with a line molecule as core was synthesized.•A bi-armed TPA-based molecule with the same core was also studied.•The four-armed molecule presents better miscibility with PCBM.•The OSCs based on the four-armed molecule donor show better device performances.A novel four-armed triphenylamine (TPA)-based molecule named (TPATh)4TPA2B with 4,7-bis(4-diphenylaminophenyl)-2,1,3-benzothiadiazole unit as the central building block and triphenylamine-3-dodecylthiophene unit as the arms and a bi-armed TPA-based molecule named (TPATh)2(MTPA)2B with the same central building block and arms as those of (TPATh)4TPA2B were designed and synthesized by Pd-catalyzed Stille reaction. The thermal stability, photophysical and electrochemical properties of these small molecules are studied. Moreover, they are evaluated in solution processed bulk-heterojunction organic solar cells (OSCs). The device performances of the OSCs based on these small molecule donors and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) were studied. With the same core, the four-armed molecule has the higher absorption and better miscibility with PC71BM than that of bi-armed molecule, while the bi-armed molecule (TPATh)2(MTPA)2B has the higher hole mobility. The power conversion efficiency of the OSCs based on (TPATh)4TPA2B as donor and PC71BM as acceptor is 1.3% with open-circuit voltage 0.71 V.

To explore enhancing photocurrent in organic solar cells (OSCs) via harvesting triplet excitons, two novel bicycloiridium complexes (R1 and R2) are designed and synthesized. Conventional bulk-heterojunction triplet OSCs are solution processed using R1 or R2 as sole electron donors and phenyl-C71-butyric acid methyl ester (PC71BM) as the electron acceptor. A decent short circuit current (Jsc) of 6.5 mA cm−2 is achieved though the overlap between the absorption spectrum (with ∼550 nm absorption onset) of R2 and the solar flux is relatively small. With an open circuit voltage of 0.74 V and a fill factor of 0.42, an encouraging power conversion efficiency of 2.0% is achieved in the OSCs based on R2 and PC71BM without any processing additives and post-treatments. Our preliminary result demonstrates the possibility of utilizing Ir complexes as sole electron donors in OSCs, which extends available soluble small molecules for OSCs.

2D TiO2–WO3 composite inverse opal (IO) films on ITO substrates were prepared by using a surfactant-free co-assembly route using a template of polystyrene (PS) spheres with a diameter of 900 nm. Thus obtained TiO2–WO3 composite IO films were dye sensitized for the construction of photochromic devices which exhibited good photochromic properties.

A new four-armed molecule Th4(DTPAB) with a triphenylamine–benzothiadiazole–triphenylamine unit as the core and 4-hexylthiophene as arms was synthesized. Solution-processed organic solar cells based on blends of Th4(DTPAB) and PC71BM demonstrate a power conversion efficiency of 3.18% with a high open circuit voltage of 0.96 V.

We demonstrate a simple rubbing hole injection layer (HIL) to form surface relief gratings (SRGs) on the functional layers of polymer solar cells (PSCs). PSCs studied in this work consist of an ITO/PEDOT:PSS(HIL)/P3HT:PCBM(photoactive layer)/LiF/Al structure. SRGs are successfully formed on HIL in an effective rubbing process, and are over printed on the photoactive layer and cathode consequently. These triplet SRGs change the morphologies of interfaces of PSCs, which can increase optical path lengths, interaction between HIL and P3HT chains, and interface areas between electrode and photoactive layer. Both light trapping and electrical improvement are confirmed by theory and experiments, which lead to overall increase in short-circuit current density, fill factor, and power conversion efficiency (PCE) of PSCs. An average PCE of 3.8% is achieved from PSCs with SRGs without thermal annealing. Different from the directly rubbing the donor polymer film, a suitable degree of orientation of P3HT presents a lower dichroic ratio and higher photovoltaic response in our work.Keywords: electrical improvement; hole mobility; interface area; optical path length; polymer solar cell; surface relief grating;

A new four-armed molecule Th4(DTPAB) with a triphenylamine–benzothiadiazole–triphenylamine unit as the core and 4-hexylthiophene as arms was synthesized. Solution-processed organic solar cells based on blends of Th4(DTPAB) and PC71BM demonstrate a power conversion efficiency of 3.18% with a high open circuit voltage of 0.96 V.

To explore enhancing photocurrent in organic solar cells (OSCs) via harvesting triplet excitons, two novel bicycloiridium complexes (R1 and R2) are designed and synthesized. Conventional bulk-heterojunction triplet OSCs are solution processed using R1 or R2 as sole electron donors and phenyl-C71-butyric acid methyl ester (PC71BM) as the electron acceptor. A decent short circuit current (Jsc) of 6.5 mA cm−2 is achieved though the overlap between the absorption spectrum (with ∼550 nm absorption onset) of R2 and the solar flux is relatively small. With an open circuit voltage of 0.74 V and a fill factor of 0.42, an encouraging power conversion efficiency of 2.0% is achieved in the OSCs based on R2 and PC71BM without any processing additives and post-treatments. Our preliminary result demonstrates the possibility of utilizing Ir complexes as sole electron donors in OSCs, which extends available soluble small molecules for OSCs.