Improving charge extraction and suppressing charge recombination are critically important to minimize the loss of absorbed photons and improve the device performance of polymer solar cells (PSCs). In this work, highly efficient PSCs are demonstrated by progressively improving the charge extraction and suppressing the charge recombination through the combination of side‐chain engineering of new nonfullerene acceptors (NFAs), adopting ternary blends, and introducing volatilizable solid additives. The 2D side chains on BTP‐Th induce a certain steric hindrance for molecular packing and phase separation, which is mitigated by fluorination of side chains on BTP‐FTh. Moreover, by introducing two highly crystalline molecules as the second acceptor and volatilizable solid additive, respectively, into the BTP‐FTh‐based host blend, the molecular crystallinity is significantly improved and the blend morphology is finely optimized. As expected, enhanced charge extraction and suppressed charge recombination are progressively realized, contributing to the largely improved fill factor (FF) of the resultant devices. Accompanied by the enhanced open‐circuit voltage (Voc) and short‐circuit current density (Jsc), a record high power conversion efficiency (PCE) of 19.05% is realized finally.

Realizing 19.05% Efficiency Polymer Solar Cells by Progressively Improving Charge Extraction and Suppressing Charge Recombination

A critical review on semitransparent organic solar cells

A series of ternary organic photovoltaics (OPVs) are fabricated with one wide bandgap polymer D18-Cl as donor, and well compatible Y6 and Y6-1O as acceptor. The open-circuit-voltage (VOC ) of ternary OPVs is monotonously increased along with the incorporation of Y6-1O, indicating that the alloy state should be formed between Y6 and Y6-1O due to their excellent compatibility. The energy loss can be minimized by incorporating Y6-1O, leading to the VOC improvement of ternary OPVs. By finely adjusting the Y6-1O content, a power conversion efficiency of 17.91% is achieved in the optimal ternary OPVs with 30 wt% Y6-1O in acceptors, resulting from synchronously improved short-circuit-current density (JSC ) of 25.87 mA cm-2, fill factor (FF) of 76.92% and VOC of 0.900 V in comparison with those of D18-Cl : Y6 binary OPVs. The JSC and FF improvement of ternary OPVs should be ascribed to comprehensively optimal photon harvesting, exciton dissociation and charge transport in ternary active layers. The more efficient charge separation and transport process in ternary active layers can be confirmed by the magneto-photocurrent and impedance spectroscopy experimental results, respectively. This work provides new insight into constructing highly efficient ternary OPVs with well compatible Y6 and its derivative as acceptor.

Approaching 18% efficiency of ternary organic photovoltaics with wide bandgap polymer donor and well compatible Y6 : Y6-1O as acceptor.

Since the world-record power conversion efficiency of 15.7% was achieved for organic solar cells (OSCs) in 2019, the newly developed non-fullerene acceptor (NFA) Y6 with an A-DA′D-A structure (A denotes an electron-accepting moiety, D denotes an electron-donating moiety) has attracted increasing attention. Subsequently, many new A-DA′D-A NFAs have been designed and synthesized, and the A-DA′D-A NFAs have played a significant role in the development of high-performance non-fullerene organic solar cells (NF-OSCs). Compared with the classical A-D-A-type acceptors, A-DA′D-A NFAs contain an electron-deficient core (such as benzothiadiazole (BT), benzotriazole (BTA), quinoxaline (Qx), or their derivatives) in the ladder-type fused rings to fine-tune the energy levels, broaden light absorption and achieve higher electron mobility of the NFAs. This review emphasizes the recent progress on these emerging A-DA′D-A (including Y-series) NFAs. The synthetic methods of DA′D-fused rings are introduced. The relationships between the chemical structure of the A-DA′D-A NFAs and the photovoltaic performance of the corresponding OSCs are summarized and discussed. Finally, issues and prospects for further improving photovoltaic performance of the OSCs are also proposed.

A-DA′D-A non-fullerene acceptors for high-performance organic solar cells

The use of photovoltaic technologies has been regarded as a promising approach for converting solar energy to electricity and mitigating the energy crisis, and among these, organic photovoltaics (O...

n-Type Molecular Photovoltaic Materials: Design Strategies and Device Applications.

The ternary strategy exhibits great potential in optimizing the photon harvesting and phase separation of active layers. In this work, non-fullerene MF1 was selected as the third component to prepare efficient ternary organic solar cells (OSCs) by finely optimizing the MF1 content in the acceptors. The optimized power conversion efficiency (PCE) of 15.31% is achieved in the ternary OSCs with 20 wt% MF1 content in the acceptors and 100 nm active layer thickness, also exhibiting a relatively high fill factor (FF) of 78.05%. The relatively high FF indicates efficient charge transport and collection in the optimized ternary OSCs, which should be beneficial to achieve efficient thick-film OSCs. It is highlighted that a PCE of 14.57% is achieved in the optimized ternary OSCs with 300 nm thick active layers compatible with the roll-to-roll (R2R) large-scale printing process. To date, high performance thick-film ternary non-fullerene OSCs have seldom been reported. This work indicates that the thick-film ternary strategy has great potential in achieving efficient large-scale OSCs.

Over 14.5% efficiency and 71.6% fill factor of ternary organic solar cells with 300 nm thick active layers

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

Semitransparent organic solar cells (OSCs) were fabricated with a broad bandgap polymer D18-Cl as the donor (D), narrow bandgap small molecule Y6-1O as the acceptor (A) and ultra-narrow bandgap material Y6 as the third component. A power conversion efficiency (PCE) of 14.92% can be obtained from opaque OSCs with D18-Cl:Y6-1O (1.1 : 1.6, wt/wt or 0.7 : 1.6, wt/wt) as active layers, which is due to the dependence of the three well-balanced photovoltaic parameters on D18-Cl content in the active layer. It should be highlighted that the average visible transmittance (AVT) of blend films can be markedly enhanced from 30.3% to 47.3% with decrease in D:A from 1.1 : 1.6 to 0.7 : 1.6 (wt/wt), which is highly conducive to the preparation of semitransparent OSCs. Keeping the D:A as constant (0.7 : 1.6, wt/wt), 16.05% PCE is achieved in opaque ternary OSCs with D18-Cl:Y6-1O:Y6 (0.7 : 0.8 : 0.8, wt/wt) as the active layers, resulting from the slightly increased JSC of 23.21 mA cm−2 and FF of 76.74%. The AVT of the corresponding ternary blend films is also improved to 50.1%. Semitransparent ternary OSCs are fabricated with Au (1 nm)/Ag (20 nm, 15 nm, 10 nm) replacing 100 nm Ag as the electrode. A PCE of 13.02%, an AVT of 20.2% and light utilization efficiency of 2.63% are obtained from the semitransparent OSCs with Au (1 nm)/Ag (10 nm) as the electrode. This work indicates that adjusting D:A weight ratio and employing a ternary strategy should have great potential in simultaneously improving the PCE and AVT of semitransparent OSCs, especially using a wide bandgap polymer as the donor.

Xuelin Wang

Papers

Over 14.5% efficiency and 71.6% fill factor of ternary organic solar cells with 300 nm thick active layers

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

Semitransparent organic solar cells exhibiting 13.02% efficiency and 20.2% average visible transmittance

Over 17.7% efficiency ternary-blend organic solar cells with low energy-loss and good thickness-tolerance

Ternary Organic Photovoltaic Cells Exhibiting 17.59% Efficiency with Two Compatible Y6 Derivations as Acceptor