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

Ternary strategy has been considered as an efficient method to achieve high performance polymer solar cells (PSCs). A power conversion efficiency (PCE) of 17.22% is achieved in the optimized ternary PSCs with 10 wt% MF1 in acceptors. The over 8% PCE improvement by employing ternary strategy is attributed to the simultaneously increased JSC of 25.68 mA cm−2, VOC of 0.853 V and FF of 78.61% compared with Y6 based binary PSCs. The good compatibility of MF1 and Y6 can be confirmed from Raman mapping, contact angle, cyclic voltammetry and morphology, which is the prerequisite to form alloy-like state. Electron mobility in ternary active layers strongly depends on MF1 content in acceptors due to the different lowest unoccupied molecular orbital (LUMO) levels of Y6 and MF1, which can well explain the wave-like varied FF of ternary PSCs. The third-party certified PCE of 16.8% should be one of the highest values for single bulk heterojunction PSCs. This work provides sufficient references for selecting materials to achieve efficient ternary PSCs.

Alloy-like ternary polymer solar cells with over 17.2% efficiency

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.

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

Recent Progress on Broadband Organic Photodetectors and their Applications

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

Broad response organic photodetectors (OPDs) with a photomultiplication (PM) effect are achieved with one absorber layer and one multiplication layer. The response range of the PM-OPDs is primarily determined by materials in the absorber layer, and the external quantum efficiency (EQE) of the PM-OPDs is mainly controlled by the multiplication layer. Here, double-layered PM-OPDs were designed with an ITO/ZnO/PM6:Y6/PC71BM:P3HT (100:5, w/w)/Au structure, where PM6:Y6 is employed as an absorber layer and PC71BM:P3HT is used as a multiplication layer. The optimal PM-OPDs exhibit a broad response covering 350-950 nm. Meanwhile, the optimal PM-OPDs exhibit the largest EQE value of ∼1200% and a maximum specific detectivity (D*) of ∼6.8 × 10-12 cm Hz1/2 W-1 under a 10 V bias. This double-layered approach may be a smart strategy for realizing PM-OPDs with an easily adjustable response range.

Photomultiplication Type Broad Response Organic Photodetectors with One Absorber Layer and One Multiplication Layer.

Highly Sensitive Narrowband Photomultiplication-Type Organic Photodetectors Prepared by Transfer-Printed Technology

Photomultiplication (PM) type organic photodetectors (OPDs) based on electron tunneling injection are achieved with a specific structure of ITO/ZnO/PC71BM:P3HT (100 : 5, wt/wt)/Au and can work well under forward and reverse bias. A rather low dark current density of the PM type OPDs is obtained due to the large electron injection barrier of 0.7 eV from the ITO electrode or 1.1 eV from the Au electrode, as well as the absence of continuous hole transport channels in the active layers. The external quantum efficiency (EQE) spectral shape of PM type OPDs can be easily adjusted by altering the bias polarity and active layer thickness, which can be well explained by the trapped hole distribution near the ITO and Au electrodes, respectively. The PM type OPDs with 400 nm active layers exhibit the maximum EQE of 3900% and 4900% under 5 V and −5 V bias, respectively. This work firstly achieves PM type OPDs with electron-only transport properties, which has great potential to well match with other organic electronic devices.

Zijin Zhao

Papers

Recent Progress on Broadband Organic Photodetectors and their Applications

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

Photomultiplication Type Broad Response Organic Photodetectors with One Absorber Layer and One Multiplication Layer.

Highly Sensitive Narrowband Photomultiplication-Type Organic Photodetectors Prepared by Transfer-Printed Technology

Photomultiplication type organic photodetectors based on electron tunneling injection