18% Efficiency organic solar cells

Optimizing the molecular structures of organic photovoltaic (OPV) materials is one of the most effective methods to boost power conversion efficiencies (PCEs). For an excellent molecular system with a certain conjugated skeleton, fine tuning the alky chains is of considerable significance to fully explore its photovoltaic potential. In this work, the optimization of alkyl chains is performed on a chlorinated nonfullerene acceptor (NFA) named BTP-4Cl-BO (a Y6 derivative) and very impressive photovoltaic parameters in OPV cells are obtained. To get more ordered intermolecular packing, the n-undecyl is shortened at the edge of BTP-eC11 to n-nonyl and n-heptyl. As a result, the NFAs of BTP-eC9 and BTP-eC7 are synthesized. The BTP-eC7 shows relatively poor solubility and thus limits its application in device fabrication. Fortunately, the BTP-eC9 possesses good solubility and, at the same time, enhanced electron transport property than BTP-eC11. Significantly, due to the simultaneously enhanced short-circuit current density and fill factor, the BTP-eC9-based single-junction OPV cells record a maximum PCE of 17.8% and get a certified value of 17.3%. These results demonstrate that minimizing the alkyl chains to get suitable solubility and enhanced intermolecular packing has a great potential in further improving its photovoltaic performance.

Single-Junction Organic Photovoltaic Cells with Approaching 18% Efficiency.

Molecular design of non-fullerene acceptors is of vital importance for high-efficiency organic solar cells. The branched alkyl chain modification is often regarded as a counter-intuitive approach, as it may introduce an undesirable steric hindrance that reduces charge transport in non-fullerene acceptors. Here we show the design and synthesis of a highly efficient non-fullerene acceptor family by substituting the beta position of the thiophene unit on a Y6-based dithienothiophen[3,2-b]-pyrrolobenzothiadiazole core with branched alkyl chains. It was found that such a modification to a different alkyl chain length could completely change the molecular packing behaviour of non-fullerene acceptors, leading to improved structural order and charge transport in thin films. An unprecedented efficiency of 18.32% (certified value of 17.9%) with a fill factor of 81.5% is achieved for single-junction organic solar cells. This work reveals the importance of the branched alkyl chain topology in tuning the molecular packing and blend morphology, which leads to improved organic photovoltaic performance. Molecular design of acceptor and donor molecules has enabled major progress in organic photovoltaics. Li et al. show that branched alkyl chains in non-fullerene acceptors allow favourable morphology in the active layer, enabling a certified device efficiency of 17.9%.

Non-fullerene acceptors with branched side chains and improved molecular packing to exceed 18% efficiency in organic solar cells

Improving power conversion efficiency (PCE) is important for broadening the applications of organic photovoltaic (OPV) cells. Here, a maximum PCE of 19.0% (certified value of 18.7%) is achieved in single-junction OPV cells by combining material design with a ternary blending strategy. An active layer comprising a new wide-bandgap polymer donor named PBQx-TF and a new low-bandgap non-fullerene acceptor (NFA) named eC9-2Cl is rationally designed. With optimized light utilization, the resulting binary cell exhibits a good PCE of 17.7%. An NFA F-BTA3 is then added to the active layer as a third component to simultaneously improve the photovoltaic parameters. The improved light unitization, cascaded energy level alignment, and enhanced intermolecular packing result in open-circuit voltage of 0.879 V, short-circuit current density of 26.7 mA cm-2 , and fill factor of 0.809. This study demonstrates that further improvement of PCEs of high-performance OPV cells requires fine tuning of the electronic structures and morphologies of the active layers.

Single-Junction Organic Photovoltaic Cell with 19% Efficiency

Solar cell efficiency tables (version 57)

Over 13% Efficiency Ternary Nonfullerene Polymer Solar Cells with Tilted Up Absorption Edge by Incorporating a Medium Bandgap Acceptor

Thiolactone copolymer donor gifts organic solar cells a 16.72% efficiency

Wide Bandgap Polymer with Narrow Photon Harvesting in Visible Light Range Enables Efficient Semitransparent Organic Photovoltaics

Citation: K Jin, Z Xiao, and L M Ding, 18.69% PCE from organic solar cells[J]. J. Semicond., 2021, 42(6), 060502. http://doi.org/ 10.1088/1674-4926/42/6/060502  The exquisite design and persistent development of fused-ring-acceptor-unit-based copolymer donors and Yseries nonfullerene acceptors (NFAs) have pushed the power conversion efficiencies (PCEs) for organic solar cells onto the 18% level[1−21]. Our group invented copolymer donors D18 and D18-Cl[2, 3]. D18:Y6, D18-Cl:N3 and D18:N3 solar cells have delivered outstanding PCEs of 18.22%, 18.13% and 18.56%, respectively[2−4]. Ternary solar cells based on a polymer donor, a NFA and a fullerene acceptor show great potential since they combine good light-harvesting capability of NFA and good electron-mobility of fullerene[5]. In this report, the device structure is ITO/PEDOT:PSS/D18Cl:N3:PC61BM (D:A1:A2)/PDIN/Ag. The D : A1 ratio was fixed at 1 : 1.4 (wt) since D18-Cl:N3 cells gave the best performance at the ratio of 1 : 1.4[3]. We adjusted PC61BM content from 0.1 to 0.2 to 0.3. When D : A1 : A2 ratio was 1 : 1.4 : 0.1, the ternary cells gave the highest PCE (Table S1). The champion cells with 0.3 vol% diphenyl ether (DPE) as the additive and an active layer thickness of 114 nm gave the highest PCE of 18.69%, with an open-circuit voltage (Voc) of 0.849 V, a shortcircuit current density (Jsc) of 28.22 mA cm–2 and a fill factor (FF) of 78.0% (Table S2, Table S3 and Fig. S1). The external quantum efficiency (EQE) exceeded 80% in 450–840 nm, with a maximum of 91% at 540 nm (Fig. S2). The integrated photocurrent density is 27.24 mA cm–2. The best devices were also measured at the National Institute of Metrology (NIM), Beijing, and a certified PCE of 18.1% (Voc, 0.854 V; Jsc, 27.36 mA cm–2; FF, 77.3%; effective area, 2.580 mm2) was recorded (Fig. S3). To the best of our knowledge, the 18.1% certified efficiency is the highest value reported for organic solar cells to date. Compared with the binary cells, the ternary cells show simultaneously enhanced Jsc and FF, suggesting the improved charge transport in the active layer. We measured hole and electron mobilities (μh and μe) by using the space charge limited current (SCLC) method (Fig. S4, Fig. S5 and Table S4). From binary to ternary blend films, μh didn’t change much while μe increased from 6.32 × 10–4 to 7.42 × 10–4 cm2 V–1 s–1. Fullerene enhanced electron transport and led to more balanced charge transport (Table S4).

https://iopscience.iop.org/article/10.1088/1674-4926/42/6/060502/pdf

Ke Jin

Papers

18% Efficiency organic solar cells

Over 13% Efficiency Ternary Nonfullerene Polymer Solar Cells with Tilted Up Absorption Edge by Incorporating a Medium Bandgap Acceptor

Thiolactone copolymer donor gifts organic solar cells a 16.72% efficiency

Wide Bandgap Polymer with Narrow Photon Harvesting in Visible Light Range Enables Efficient Semitransparent Organic Photovoltaics

18.69% PCE from organic solar cells