Yunpeng Qin

Fine-Tuned Photoactive and Interconnection Layers for Achieving over 13% Efficiency in a Fullerene-Free Tandem Organic Solar Cell

Fabricating organic solar cells (OSCs) with a tandem structure has been considered an effective method to overcome the limited light absorption spectra of organic photovoltaic materials. Currently, the most efficient tandem OSCs are fabricated by adopting fullerene derivatives as acceptors. In this work, we designed a new non-fullerene acceptor with an optical band gap (Egopt) of 1.68 eV for the front subcells and optimized the phase-separation morphology of a fullerene-free active layer with an Egopt of 1.36 eV to fabricate the rear subcell. The two subcells show a low energy loss and high external quantum efficiency, and their photoresponse spectra are complementary. In addition, an interconnection layer (ICL) composed of ZnO and a pH-neutral self-doped conductive polymer, PCP-Na, with high light transmittance in the near-IR range was developed. From the highly optimized subcells and ICL, solution-processed fullerene-free tandem OSCs with an average power conversion efficiency (PCE) greater than 13% were obtained.

Design and Synthesis of a Low Bandgap Small Molecule Acceptor for Efficient Polymer Solar Cells

A novel non-fullerene acceptor, possessing a very low bandgap of 1.34 eV and a high-lying lowest unoccupied molecular orbital level of -3.95 eV, is designed and synthesized by introducing electron-donating alkoxy groups to the backbone of a conjugated small molecule. Impressive power conversion efficiencies of 8.4% and 10.7% are obtained for fabricated single and tandem polymer solar cells.

Efficient Charge Transfer and Fine-Tuned Energy Level Alignment in a THF-Processed Fullerene-Free Organic Solar Cell with 11.3% Efficiency.

Fullerene-free organic solar cells show over 11% power conversion efficiency, processed by low toxic solvents. The applied donor and acceptor in the bulk heterojunction exhibit almost the same highest occupied molecular orbital level, yet exhibit very efficient charge creation.

Highly Efficient Fullerene-Free Polymer Solar Cells Fabricated with Polythiophene Derivative

A highly efficient fullerene-free polymer solar cell (PSC) based on PDCBT, a polythiophene derivative substituted with alkoxycarbonyl, achieves an impressive power conversion efficiency of 10.16%, which is the best result in PSCs based on polythiophene derivatives to date. In comparison with a poly(3-hexylthiophene):ITIC-based device, the photovoltaic and morphological properties of the PDCBT:ITIC-based device are carefully investigated and interpreted.

Over 11% Efficiency in Tandem Polymer Solar Cells Featured by a Low‐Band‐Gap Polymer with Fine‐Tuned Properties

Highly efficient polymer solar cells with tandem structure are fabricated by using two excellent photovoltaic polymers and a highly transparent intermediate recombination layer. Power conversion efficiencies over 11% can be realized featured by a low-band-gap polymer with fine-tuned properties.

Over 14% Efficiency in Polymer Solar Cells Enabled by a Chlorinated Polymer Donor

Fluorine-contained polymers, which have been widely used in highly efficient polymer solar cells (PSCs), are rather costly due to their complicated synthesis and low yields in the preparation of components. Here, the feasibility of replacing the critical fluorine substituents in high-performance photovoltaic polymer donors with chlorine is demonstrated, and two polymeric donors, PBDB-T-2F and PBDB-T-2Cl, are synthesized and compared in parallel. The synthesis of PBDB-T-2Cl is much simpler than that of PBDB-T-2F. The two polymers have very similar optoelectronic and morphological properties, except the chlorinated polymer possess lower molecular energy levels than the fluorinated one. As a result, the PBDB-T-2Cl-based PSCs exhibit higher open circuit voltage (Voc ) than the PBDB-T-2F-based devices, leading to an outstanding power conversion efficiency of over 14%. This work establishes a more economical design paradigm of replacing fluorine with chlorine for preparing highly efficient polymer donors.

Achieving 12.8% Efficiency by Simultaneously Improving Open-Circuit Voltage and Short-Circuit Current Density in Tandem Organic Solar Cells

Tandem organic solar cells (TOSCs), which integrate multiple organic photovoltaic layers with complementary absorption in series, have been proved to be a strong contender in organic photovoltaic depending on their advantages in harvesting a greater part of the solar spectrum and more efficient photon utilization than traditional single-junction organic solar cells. However, simultaneously improving open circuit voltage (Voc ) and short current density (Jsc ) is a still particularly tricky issue for highly efficient TOSCs. In this work, by employing the low-bandgap nonfullerene acceptor, IEICO, into the rear cell to extend absorption, and meanwhile introducing PBDD4T-2F into the front cell for improving Voc , an impressive efficiency of 12.8% has been achieved in well-designed TOSC. This result is also one of the highest efficiencies reported in state-of-the-art organic solar cells.

Perovskite-polymer hybrid solar cells with near-infrared external quantum efficiency over 40%

In the past several years, conjugated polymers and organometal halide perovskites have become regarded as promising light-absorbing materials for next-generation photovoltaic devices and have attracted a great deal of interest. As the main part of this contribution, we describe the enhancement of near-infrared (NIR) photoresponse of well-known CH3NH3PbI3−xClx-based solar cells by the integration of bulk heterojunction (BHJ) small band gap polymer:fullerene absorbers. Particularly, the integration of a commercially available polymer PDPP3T and PCBM-based BHJ boosts the peak external quantum efficiency (EQE) by up to 46% in the NIR region (800−1000 nm), which is outside of the photoresponsive region (300−800 nm) of conventional perovskite solar cells. This substantial improvement in the EQE over the NIR region offers an additional current density of ∼5 mA cm−2 for the control perovskite solar cell, and a high power conversion efficiency (PCE) of over 12% was obtained in the perovskite/BHJ-based solar cells. In addition, the insertion of the BHJ absorber consisting of a small band gap polymer PDTP-DFBT and PCBM also results in nearly 40% EQE for the perovskite/BHJ solar cell. The results also reveal that controlling over the polymer/PCBM weight ratio for a BHJ absorber is the key to achieving the optimal efficiency for this type of perovskite-polymer hybrid solar cell.中文摘要近年来, 共轭聚合物和钙钛矿型有机金属卤化物被视为极具潜力的光伏材料, 引起了广泛的研究兴趣. 本文通过引入两种本体异质结(BHJ)聚合物: 富勒烯活性层, 大幅提高了基于CH3NH3PbI3−x的钙钛矿太阳能电池的近红外光响应特性. 其中, 基于窄带隙聚合物PDPP3T的钙钛矿/BHJ杂化太阳能电池在近红外区域(800∼1000 nm)内的外量子效率(EQE)峰值高达46%, 且该区域已经超出了CH3NH3PbI3−x型太阳能电池的光响应范围(300∼800 nm). 相较于参照的钙钛矿太阳能电池, 近红外区域大幅提升的EQE为钙钛矿/BHJ杂化太阳能电池贡献了额外的电流密度(∼5 mA cm−2), 因此其光电转换效率达到了12%以上. 此外, 引入基于聚合物PDTP-DFBT的BHJ也可以使钙钛矿太阳能电池在近红外区域的EQE达到40%以上. 研究结果也表明优化BHJ的聚合物: 富勒烯比例是提高这类钙钛矿-聚合物杂化太阳能电池性能的关键.

A Highly Efficient Non-Fullerene Organic Solar Cell with a Fill Factor over 0.80 Enabled by a Fine-Tuned Hole-Transporting Layer

With rapid development for tens of years, organic solar cells (OSCs) have attracted much attention for their potential in practical applications. As an important photovoltaic parameter, the fill factor (FF) of OSCs stands for the effectiveness of charge generation and collection, which significantly depends on the properties of the interlayer and active layer. Here, a facile and effective strategy to improve the FF through hole-transporting layer (HTL) modification is demonstrated. By mixing WOx nanoparticles with a poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) emulsion, the surface free energy of the HTL is improved and the morphology of the active layer is optimized. Benefiting from increased carrier lifetime, a device based on WOx :PEDOT:PSS HTL exhibits a boosted performance with an FF of 80.79% and power conversion efficiency of 14.57% PCE. The results are certified by the National Institute of Metrology (NIM), which, to date, are the highest values in this field with certification. This work offers a simple and viable option of HTL modification to realize highly efficient OSCs.

Fluorination vs. chlorination: a case study on high performance organic photovoltaic materials

Halogenation is a very efficient chemical modification method to tune the molecular energy levels, absorption spectra and molecular packing of organic semiconductors. Recently, in the field of organic solar cells (OSCs), both fluorine- and chlorinesubstituted photovoltaic materials, including donors and acceptors, demonstrated their great potentials in achieving high power conversion efficiencies (PCEs), raising a question that how to make a decision between fluorination and chlorination when designing materials. Herein, we systemically studied the impact of fluorination and chlorination on the properties of resulting donors (PBDB-T-2F and PBDB-T-2Cl) and acceptors (IT-4F and IT-4Cl). The results suggest that all the OSCs based on different donor and acceptor combinations can deliver good PCEs around 13%–14%. Chlorination is more effective than fluorination in downshifting the molecular energy levels and broadening the absorption spectra. The influence of chlorination and fluorination on the crystallinity of the resulting materials is dependent on their introduction positions. As chlorination has the advantage of easy synthesis, it is more attractive in designing low-cost photovoltaic materials and therefore may have more potential in largescale applications.