Advances in the design and application of highly efficient conjugated polymers and small molecules over the past years have enabled the rapid progress in the development of organic photovoltaic (OPV) technology as a promising alternative to conventional solar cells. Among the numerous OPV materials, benzodithiophene (BDT)-based polymers and small molecules have come to the fore in achieving outstanding power conversion efficiency (PCE) and breaking 10% efficiency barrier in the single junction OPV devices. Remarkably, the OPV device featured by BDT-based polymer has recently demonstrated an impressive PCE of 11.21%, indicating the great potential of this class of materials in commercial photovoltaic applications. In this review, we offered an overview of the organic photovoltaic materials based on BDT from the aspects of backbones, functional groups, alkyl chains, and device performance, trying to provide a guideline about the structure-performance relationship. We believe more exciting BDT-based photovol...

Molecular Design of Benzodithiophene-Based Organic Photovoltaic Materials.

Morphology Control in Organic Solar Cells

To understand the vertical phase separation in the bulk junction active layer of organic photovoltaic devices is essential for controlling the charge transfer behavior and achieving effective charge collection. Here, diphenyl sulfide (DPS) was introduced as a novel additive into the PTB7-Th:PC71BM-based inverted polymer solar cells (PSCs), and the effect of additives on active blend films and photovoltaic characteristics was carefully studied. The results show that DPS could not only modulate the vertical composition distribution but also promote the ordered molecular packing of the photoactive layer, thus effectively improving exciton dissociation, charge transport, and collection, and thus exhibit an excellent power conversion efficiency of 9.7% with an improved fill factor (>70%) after using 3% DPS additive. The results show that the DPS solvent additive can effectively adjust the vertical phase distribution and crystallinity of blend films and improve the photovoltaic performance of the inverted organ...

Enhanced Organic Photovoltaic Performance through Modulating Vertical Composition Distribution and Promoting Crystallinity of the Photoactive Layer by Diphenyl Sulfide Additives.

Organic–inorganic hybrid perovskite solar cells (PSCs) has achieved the power conversion efficiency (PCE) of 25.2% in the last 10 years, and the PCE of inverted PSCs has reached >22%. The rapid enh...

Recent Progress of Inverted Perovskite Solar Cells with a Modified PEDOT:PSS Hole Transport Layer.

The current work reports the lithium (Li) doping of a low-temperature processed zinc oxide (ZnO) electron transport layer (ETL) for highly efficient, triple-cation-based MA0.57FA0.38Rb0.05PbI3 (MA: methylammonium, FA: formamidinium, Rb: rubidium) perovskite solar cells (PSCs). Lithium intercalation in the host ZnO lattice structure is dominated by interstitial doping phenomena, which passivates the intrinsic defects in ZnO film. In addition, interstitial Li doping also downshifts the Fermi energy position of Li-doped ETL by 30 meV, which contributes to the reduction of the electron injection barrier from the photoactive perovskite layer. Compared to the pristine ZnO, the power conversion efficiency (PCE) of the PSCs incorporating lithium-doped ZnO (Li-doped) is raised from 14.07 to 16.14%. The superior performance is attributed to the reduced current leakage, enhanced charge extraction characteristics, and mitigated trap-assisted recombination phenomena in Li-doped devices, thoroughly investigated by mean...

Solution-Processed Lithium-Doped ZnO Electron Transport Layer for Efficient Triple Cation (Rb, MA, FA) Perovskite Solar Cells

In this paper, we investigate the effects of glycerol doping on transmittance, conductivity and surface morphology of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate)) (PEDOT:PSS) and its influence on the performance of perovskite solar cells. . The conductivity of PEDOT:PSS is improved obviously by doping glycerol. The maximum of the conductivity is 0.89 S/cm when the doping concentration reaches 6 wt%, which increases about 127 times compared with undoped. The perovskite solar cells are fabricated with a configuration of indium tin oxide (ITO)/PEDOT:PSS/CH3NH3PbI3/PC61BM/Al, where PEDOT:PSS and PC61BM are used as hole and electron transport layers, respectively. The results show an improvement of hole charge transport as well as an increase of short-circuit current density and a reduction of series resistance, owing to the higher conductivity of the doped PEDOT:PSS. Consequently, it improves the whole performance of perovskite solar cell. The power conversion efficiency (PCE) of the device is improved from 8.57% to 11.03% under AM 1.5 G (100 mW/cm2 illumination) after the buffer layer has been modified.

http://iopscience.iop.org/article/10.1088/1674-1056/25/2/028402/pdf

Improving the performance of perovskite solar cells with glycerol-doped PEDOT:PSS buffer layer*

Two low band gap (LBG) copolymers PCz-DTBTT and PICz-DTBTT, featuring a modified 2,1,3-benzothiadiazole–thiophene-cored unit 2,5-di(4-(4-octylthiophen-2-yl)-2,1,3-benzothiadiazol-7-yl)thiophene (DTBTT) as acceptor and electron-rich building blocks carbazole (Cz) or indolo[3,2-b]carbazole (ICz) as donor, were synthesized via Suzuki crossing-coupling method. Both copolymers show good solubility in common organic solvents and thermal stabilities. The optical study exhibits a broad absorption in the range of 300–700 nm with the optical band gap (
 $$E_{g}^{\text{opt}}$$
 ) of about 1.78 eV, while the electrochemical cyclic voltammetry (CV) measurement shows the relatively deeper highest occupied molecular orbital (HOMO) energy level (about −5.45 eV). Photovoltaic devices based on the blends of PCz-DTBTT/PC71BM (w:w; 1:2) and PICz-DTBTT/PC71BM (w:w; 1:2) with devices configuration as ITO/PEDOT:PSS/polymer:PC71BM/Ca/Al, show the power conversion efficiency (PCE) up to 2.07 and 2.21 %, with the open circuit voltage (V
 oc) of 0.75 and 0.80 V, short circuit current density (J
 sc) of 6.47 and 6.40 mA cm−2, fill factor (FF) of 42.6 and 43.2 % under an AM1.5 simulator (100 mW cm−2), respectively. It is apparent that DTBTT-based devices exhibit the broad response range, covering from 300 to 720 nm.

Synthesis of modified benzothiadiazole-thiophene-cored acceptor and carbazole/indolocarbazole alternating conjugated polymers and their photovoltaic applications

An alternating low band gap conjugated polymer derived from 5.10-di(2-ethylhexyloxy)dithieno[2,3-d:2’,3’-d’]benzo[1,2-b:4,5-b’]dithiophene (DTBDT) and isoindigo derivative (ID), was synthesized and characterized. The polymer exhibits good solubility in organic solvent and extensive absorption from 350 to 780 nm with the highest occupied molecular orbital (HOMO) level of −5.38 eV and lowest unoccupied molecular orbital (LUMO) level of −3.80 eV. In spite of those, the power conversion efficiency (PCE) of 0.21 % for the photovoltaic cells (PVCs) from the blend of the polymer and [6, 6]-phenyl-C71-butyric acid methyl ester (PC71BM) is very low. Interestingly, the performances of the PVCs from the polymer are remarkably increased while a very small amount of diphenyl sulfide (DPS) is used as solvent additives, and the maximal PCE of 4.43 % is achieved in the PVCs from the blend of polymer and PC71BM (W:W, 1:1.5) with DPS as solvent additives under 100 mW/cm2 illumination (AM 1.5G).

Synthesis of dithieno[2,3- d :2’,3’- d ’]benzo[1,2-b:4,5- b ’]dithiophene - alt -isoindigo conjugated polymer and enhancement of photovoltaic property with diphenyl sulfide additives

A conjugated polyelectrolyte (CPE) named PBNBr, is prepared by post-quaternizing of poly{4,8-bis(octyloxy)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-9,9-bis(3′-((N,N-dimethylamino)propyl)fluorene-2,7-diyl} (PBN) with bromoethane. The chemical strucutes, electrooptical properties of the PBNBr is fully characterized. As compared with the PBN, the PBNBr exhibit much better methanol solution processibility, and more effectively tuning ability for the work function (Wf) of ITO (WF bare ITO, −4.8 eV, WF of ITO with PBN interlayer, −4.1 eV, WF of ITO with PBNBr interlayer −3.9 eV). The open circuit voltages (VOC) and power conversion efficiencies (PCEs) of polymer solar cells from the blend film of poly(3-hexylthiophene) (P3HT) and [6,6]-phenylC61-butyric acid methyl ester (PC61BM) with PBN and/or PBNBr modified ITO as cathode are respectively increased about 27% and 120% in contrast to those for the control devices with bare ITO as cathode. And PCEs of 4.21% and 4.53% are achieved in the PSCs with PBN ...

Heng Zhang

Papers

Improving the performance of perovskite solar cells with glycerol-doped PEDOT:PSS buffer layer*

Synthesis of modified benzothiadiazole-thiophene-cored acceptor and carbazole/indolocarbazole alternating conjugated polymers and their photovoltaic applications

Synthesis of dithieno[2,3- d :2’,3’- d ’]benzo[1,2-b:4,5- b ’]dithiophene - alt -isoindigo conjugated polymer and enhancement of photovoltaic property with diphenyl sulfide additives

Benzo[1,2-b:4,5-b′]dithiophene-based conjugated polyelectrolyte for the cathode modification of inverted polymer solar cells