Jiamin Cao

A pentacyclic aromatic lactam building block for efficient polymer solar cells

A D–A conjugated polymer (PThTPTI) was developed by using a brand new pentacyclic aromatic lactam acceptor unit (TPTI). PThTPTI possesses good light absorption, thermal stability, and a deep HOMO level. PThTPTI/PC71BM cells afford an outstanding PCE up to 7.80%, with high Voc (0.87 V), Jsc (13.69 mA cm−2) and FF (65.6%), and over 70% EQE in the range of 435–640 nm.

Thermo-cleavable fullerene materials as buffer layers for efficient polymer solar cells†

A new class of thermo-cleavable fullerenes, di-tert-butyl methano[60]fullerene-61,61-dicarboxylate (DBMD), bis(2-methylhexan-2-yl) methano[60]fullerene-61,61-dicarboxylate (BMHMD), and di-tert-butyl methano[60]fullerene-61,61-dicarboxylate bis-adducts (bis-DBMD), was facilely prepared through one-step Bingel reaction from C60. At high temperature, the tertiary alkyl ester groups of the three compounds undergo thermo-cleavage processes to produce insoluble methano[60]fullerene-61-carboxylic acids (MCAs). BMHMD and bis-DBMD were applied in inverted polymer solar cells as a cathode buffer layer. Heating BMHMD or bis-DBMD films on ZnO produced MCA1 and MCA2 interfacial layers, respectively. MCA-modified ZnO possesses a smoother and more hydrophobic surface, and shows excellent solvent-resistance. The MCA buffer layer dramatically improved the device performance by enhancing Jsc and FF of the solar cells. The power conversion efficiency (PCE) increased from 3.44% (control) to 3.79% (MCA1) and 4.10% (MCA2) for a P3HT/PC61BM solar cell, and from 6.95% (control) to 7.13% (MCA1) and 7.57% (MCA2) for a PBDTTT-C/PC71BM solar cell.

An efficient selenophene-containing conjugated copolymer for organic solar cells

A D–A polymer, PSeTPTI, was developed by copolymerizing a pentacyclic acceptor unit TPTI with a selenophene unit. PSeTPTI possesses a narrow optical bandgap, a low-lying HOMO energy level, and a high hole mobility of 0.26 cm2 V−1 s−1. PSeTPTI/PC71BM solar cells demonstrate a PCE of 6.04%, which is the highest efficiency for the conjugated copolymers using selenophene as the donor unit.

Transparent and transferrable organic optoelectronic devices based on WO3/Ag/WO3 electrodes

With a thin metal film inserted between two oxide layers, the WO3/Ag/WO3 (WAW) multilayer structure owns both high transmittance and high conductivity. By carefully optimizing Ag film thickness, WAW shows high average transmittance of 82.5% in 400–750 nm range and low sheet resistance of 20 Ω/sq. Employing such WAW electrodes, transparent organic photodetectors are fabricated, and with help of a polyacrylonitrile protective layer, the devices can be smartly separated and transferred onto other substrates while maintaining their performances well. Moreover, transferrable organic solar cells are also realized with such transparent WAW electrodes.

A graphene oxide/oxygen deficient molybdenum oxide nanosheet bilayer as a hole transport layer for efficient polymer solar cells

An annealing-free hole transport layer based on oxygen deficient molybdenum oxide (MoO3−x) nanosheets was developed for polymer solar cells. It showed performance comparable to that of PEDOT:PSS. For better hole extraction, graphene oxide (GO) was introduced to form a GO/MoO3−x bilayer as a hole transport layer to further improve the device performance.

Temperature-dependent Schottky barrier in high-performance organic solar cells

Organic solar cells (OSCs) have attracted great attention in the past 30 years, and the power conversion efficiency (PCE) now reaches around 10%, largely owning to the rapid material developments. Meanwhile with the progress in the device performance, more and more interests are turning to understanding the fundamental physics inside the OSCs. In the conventional bulk-heterojunction architecture, only recently it is realized that the blend/cathode Schottky junction serves as the fundamental diode for the photovoltaic function. However, few researches have focused on such junctions, and their physical properties are far from being well-understood. In this paper based on PThBDTP:PC71BM blend, we fabricated OSCs with PCE exceeding 10%, and investigated temperature-dependent behaviors of the junction diodes by various characterization including current-voltage, capacitance-voltage and impedance measurements between 70 to 290 K. We found the Schottky barrier height exhibits large inhomogeneity, which can be described by two sets of Gaussian distributions.