Perovskite solar cells (PSCs) and organic solar cells (OSCs) are promising renewable light-harvesting technologies with high performance, but the utilization of hazardous dopants and high boiling additives is harmful to all forms of life and the environment. Herein, new multirole π-conjugated polymers (P1-P3) are developed via a rational design approach through theoretical hindsight, further successfully subjecting them into dopant-free PSCs as hole-transporting materials and additive-free OSCs as photoactive donors, respectively. Especially, P3-based PSCs and OSCs not only show high power conversion efficiencies of 17.28% and 8.26%, but also display an excellent ambient stability up to 30 d (for PSCs only), owing to their inherent superior optoelectronic properties in their pristine form. Overall, the rational approach promises to support the development of environmentally and economically sustainable PSCs and OSCs.
Small molecules based on N-atom-linked phenylcarbazole-fluorene as the main scaffold, end-capped with spirobifluorene derivatives, are developed as organic hole-transporting materials for highly efficient perovskite solar cells (PSCs) and bulk heterojunction (BHJ) inverted organic solar cells (IOSCs). The CzPAF-SBF-based devices show remarkable device performance with excellent long-term stability in PSCs and BHJ IOSCs with a maximum PCE of 17.21% and 7.93%, respectively.
Side-chain fluorination of polymers is demonstrated as a highly effective strategy to improve the efficiency of all-polymer solar cells from 2.93% (nonfluorinated P1) to 7.13% (fluorinated P2). This significant enhancement is achieved by synergistic improvements in open-circuit voltage, charge generation, and charge transport, as fluorination of the donor polymer optimizes the band alignment and the film morphology.
The performance of all-polymer solar cells (all-PSCs) is often limited by the poor exciton dissociation process. Here, the design of a series of polymer donors (P1-P3) with different numbers of fluorine atoms on their backbone is presented and the influence of fluorination on charge generation in all-PSCs is investigated. Sequential fluorination of the polymer backbones increases the dipole moment difference between the ground and excited states (Δµ ge ) from P1 (18.40 D) to P2 (25.11 D) and to P3 (28.47 D). The large Δµ ge of P3 leads to efficient exciton dissociation with greatly suppressed charge recombination in P3-based all-PSCs. Additionally, the fluorination lowers the highest occupied molecular orbital energy level of P3 and P2, leading to higher opencircuit voltage (V OC ). The power conversion efficiency of the P3-based all-PSCs (6.42%) outperforms those of the P2 and P1 (5.00% and 2.65%)-based devices. The reduced charge recombination and the enhanced polymer exciton lifetime in P3-based all-PSCs are confirmed by the measurements of light-intensity dependent short-circuit current density (J SC ) and V OC , and time-resolved photoluminescence. The results provide reciprocal understanding of the charge generation process associated with Δµ ge in all-PSCs and suggest an effective strategy for designing π-conjugated polymers for high performance all-PSCs.
Two donor−acceptor (D−A) medium band gap polymers, P1 and P2, alkoxyphenylthiophene (APTh) linked benzodithiophene (BDT) as an electron-rich unit and 1,3-di(2′-bromothien-5′-yl)-5-(2-ethylhexyl)thieno [3,4-c]pyrrole-4,6dione (TPD) (A1) or [5,6-bis(octyloxy)-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole] (BT) (A2) as an electron-deficient unit, have successfully been synthesized via microwave-assisted Stille polymerization and utilized for bulk heterojunction (BHJ) polymer solar cells (PSCs). P1 shows a well-distinguished absorption shoulder between 590 and 620 nm attributed to the π−π stacking of a polymer backbone; such kind of absorption shoulder is not observed in P2, indicating that the P1 has more planar structure than that of P2. This is due to the fact that the sulfur atom of thiophene spacer and the oxygen atom of carbonyl groups in TPD have more pronounced intramolecular noncovalent interactions (INCI) in P1 than that of the sulfur atom of thiophene spacer and the oxygen atom of alkoxy groups of BT in P2. The bulk heterojunction polymer solar cells (BHJ PSCs) were fabricated with the configuration of ITO/PEDOT:PSS/polymer (P1 or P2):PC 71 BM/LiF/Al. The P1 device shows better photovoltaic performance with open-circuit voltage (V oc ) of 0.91 V and the power conversion efficiency (PCE) of 4.19% than the P2 device (V oc : 0.71 V; PCE: 1.88%) in neat blend films under the illumination of AM 1.5G (100 mW/cm 2 ). Upon treating the active layers containing P1 and P2 with methanol, the PCE of the P1 device is increased from 4.19 to 7.14%. In contrast, the PCE of the P2 device is decreased from 1.88 to 1.82%. Space charge limited current mobility, atomic force microscopy, transmission electron microscopy, time-of-flight secondary ion mass spectrometry, and impedance spectroscopy studies strongly support the enhanced PCE for the P1 device is attributed to the increased mobility, nanoscale morphology, and reduced resistance upon methanol treatment; these favorable properties for the P1 polymer are highly correlated with the planarity of the backbone.
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