Zhongqiang Zhang

Dopant-Free Hole-Transporting Material with a C3h Symmetrical Truxene Core for Highly Efficient Perovskite Solar Cells.

Herein we present a new structural design of hole-transporting material, Trux-OMeTAD, which consists of a C3h Truxene-core with arylamine terminals and hexyl side-chains. This planar, rigid, and fully conjugated molecule exhibits excellent hole mobility and desired surface energy to the perovskite uplayer. Perovskite solar cells fabricated using the p-i-n architecture with Trux-OMeTAD as the p-layer, show a high PCE of 18.6% with minimal hysteresis.

Recent advances in perovskite solar cells: efficiency, stability and lead-free perovskite

With the rapid growth of efficiency from 3.8% to 22.1% in recent years, perovskite solar cells (PVSCs) have drawn significant attention of researchers from both academia and industry. However, significant barriers remain standing in the pathway of PVSC advancement. To develop high-efficiency and stable devices as well as environmentally benign perovskites is critical, yet challenging aspects remain in PVSC research. In this review article, we focused on the recent advances in related subjects. The approaches for high-efficiency PVSCs have been introduced and then the instability issues and lead-free perovskite have been discussed. Finally, the conclusion along with brief perspectives has been provided on further advancing PVSCs towards use in efficient and stable solar-to-electricity technologies.

Improved photon-to-electron response of ternary blend organic solar cells with a low band gap polymer sensitizer and interfacial modification

Incorporating two polymer donors with different bandgaps to compose a ternary blend bulk heterojunction (BHJ) is proved to be an effective approach to improve the device performance of BHJ polymer solar cells (PSCs). Here, we demonstrate an efficient ternary PSC consisting of a polythieno[3,4-b]-thiophene/benzodithiophene (PTB7):[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) host blend sensitized by a low band gap (LBG) polymer poly[2,7-(5,5-bis-(3,7-dimethyloctyl)-5H-dithieno[3,2-b:20,30-d]pyran)-alt-4,7-(5,6-difluoro-2,1,3-benzothiadiazole)] (PDTP-DFBT). The addition of the PDTP-DFBT sensitizer remarkably extended the PSC photon to electron response from 750 to 900 nm, which increased the Jsc from 15.12 to 16.27 mA cm−2, and the device performance from 8.08% to 8.63%. A study on the morphology involving the atomic force microscopy mapping and grazing incident X-ray diffraction showed that the incorporation of PDTP-DFBT improved the crystallinity of the PTB7 film with most of the sensitizers associated with the PTB7 domains when blending with a PC71BM film. This observation, together with the unchanged Voc of the ternary PSC, implies a sensitizing mechanism with addition of PDTP-DFBT. After further interfacial modification with a capronic acid self-assembling monolayer (C3-SAM), a higher PCE of 9.06% was achieved, which is among the highest values of efficient ternary PSCs. Our work suggests that a sensitizing mechanism of ternary blends compensates for the light absorbing limitation of binary blend PSCs for high device performance.

Energy-level modulation of non-fullerene acceptors to achieve high-efficiency polymer solar cells at a diminished energy offset

Efficient fullerene-free polymer solar cells (PSCs) are fabricated with a polymer donor PBDB-T1 and a non-fullerene acceptor ITTIC. With the incorporation of one thiophene bridge between the indacenodithienothiophene (IDTT) core and 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (IC) terminal, the new acceptor ITTIC exhibits a higher lying lowest unoccupied molecular orbital (LUMO), and a narrower bandgap than the pristine ITIC acceptor. The resultant PSCs with PBDB-T1:ITTIC blends exhibit a power conversion efficiency of 9.12%, with an increased open circuit voltage (VOC) and broader photoresponse, compared with the PBDB-T1:ITIC based devices. Interestingly, it is shown that the charge transfer remains effective at a diminished highest occupied molecular orbital (HOMO) difference of 0.02 eV between PBDB-T1 and ITTIC, leading to a mitigated energy loss of 0.54 eV in PBDB-T1:ITTIC based devices. Overall, this work provides new insights into further improvement of fullerene-free PSCs.

Vertically Oriented 2D Layered Perovskite Solar Cells with Enhanced Efficiency and Good Stability

Vertically oriented highly crystalline 2D layered (BA)2 (MA)n-1 Pbn I3n+1 (BA = CH3 (CH2 )3 NH3 , MA = CH3 NH3 , n = 3, 4) perovskite thin-films are fabricated with the aid of ammonium thiocyanate (NH4 SCN) additive through one-step spin-coating process. The humidity-stability of the film is certified by the almost unchanged X-ray diffraction patterns after exposed to humid atmosphere (Hr = 55 ± 5%) for 40 d. The photovoltaic devices with the structure of indium tin oxide(ITO)/poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate)/(BA)2 (MA)n-1 Pbn I3n+1 (n = 3,4)/[6,6]-phenyl-C61 -butyric acid methyl ester/Bathocuproine/Ag are fabricated. The devices based on (BA)2 (MA)2 Pb3 I10 perovskite (n = 3) with the precursor composition of BAI:methylammonium iodide:PbI2 :NH4 SCN = 2:2:3:1 (by molar ratio) show an averaged power conversion efficiency (PCE) of 6.82%. In the case of (BA)2 (MA)3 Pb4 I13 (n = 4), a higher PCE of 8.79% is achieved. Both of the unsealed devices perform unique stability with almost unchanged PCE during the period of storage in purified N2 glove box. This work provides a simple and effective method to enhance the efficiency of the 2D perovskite solar cell.

An aqueous solution-processed CuOX film as an anode buffer layer for efficient and stable organic solar cells

A facile and green method has been developed for the aqueous solution preparation of CuOX as an anode buffer layer for organic solar cells (OSCs). The CuOX buffer layer is prepared simply by spin-coating a copper acetylacetonate precursor based aqueous solution onto an ITO substrate at room temperature in ambient air. Hydrogen peroxide (H2O2) is used to modify the precursor aqueous solution and can greatly increase the work function of the CuOX film to improve the hole collection efficiency and the charge transport efficiency. UV-ozone post-treatment of the CuOX film leads to the fully oxidized state of copper oxide, which significantly improves the performance of OSCs. Through H2O2 modification and UV-ozone post-treatment on the CuOX anode buffer layer, the highest power conversion efficiency of the OSCs based on PTB7:PC71BM blends reaches 8.68%, which is 10% higher than that of the standard PEDOT:PSS anode buffer layer based OSCs. In addition, the devices with the CuOX buffer layer show much better air stability than those with PEDOT:PSS. Our results indicate that the aqueous solution processed CuOX with low cost and green solvents is a promising anode buffer layer material for efficient and stable OSCs.

Efficient and 1,8-diiodooctane-free ternary organic solar cells fabricated via nanoscale morphology tuning using small-molecule dye additive

The ternary strategy for incorporating multiple photon-sensitive components into a single junction has emerged as an effective method for optimizing the nanoscale morphology and improving the device performance of organic solar cells (OSCs). In this study, efficient and stable ternary OSCs were achieved by introducing the small-molecule dye (5E,5′E)-5,5′-(4′,4″-(1,2-diphenylethene-1,2-diyl)bis(biphenyl-4′,4-diyl))bis(methan-1-yl-1-ylidene)bis(3-ethyl-2-thioxothia zolidin-4-one) (BTPE-Rn) into poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-co-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th):[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) blend films processed using a 1,8-diiodooctane (DIO)-free solvent. The incorporation of BTPE-Rn enhanced the short-circuit current density and fill factor of the ternary OSCs compared with those of binary OSCs. An investigation of the optical, electronic, and morphological properties of the ternary blends indicated that the third component of BTPE-Rn not only promoted the photon utilization of blends through the energy-transfer process but also improved the electron mobility of the blends owing to the fullerene-rich nanophase optimization. More importantly, this ternary strategy of utilizing a small-molecule dye to replace the photounstable DIO additive enhanced the operational stability of the OSCs.