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The emergence of polymerized small molecule acceptors (PSMAs) has significantly improved the performance of all‐polymer solar cells (all‐PSCs). However, the pace of device engineering lacks behind that of materials development, so that a majority of the PSMAs have not fulfilled their potentials. Furthermore, most high‐performance all‐PSCs rely on the use of chloroform as the processing solvent. For instance, the recent high‐performance PSMA, named PJ1‐γ, with high LUMO, and HOMO levels, could only achieve a PCE of 16.1% with a high‐energy‐level donor (JD40) using chloroform. Herein, we present a methodology combining sequential processing (SqP) with the addition of 0.5%wt PC71BM as a solid additive (SA) to achieve an impressive efficiency of 18.0% for all‐PSCs processed from toluene, an aromatic hydrocarbon solvent. Compared to the conventional blend‐casting (BC) method whose best efficiency (16.7%) could only be achieved using chloroform, the SqP method significantly boosted the device efficiency using toluene as the processing solvent. In addition, the donor we employ is the classic PM6 that has deeper energy levels than JD40, which provides low energy loss for the device. We compare the results with another PSMA (PYF‐T‐o) with the same method. Finally, an improved photostability of the SqP devices with the incorporation of SA is demonstrated. [ABSTRACT FROM AUTHOR]

Organic solar cells (OSCs) have demonstrated over 19% power conversion efficiency (PCE) with the help of material innovation and device optimization. Co‐working with newly designed materials, traditional solvent additives, 1‐chloronaphthalene (CN), and 1,8‐diodooctane (DIO) are still powerful in morphology modulation towards satisfying efficiencies. Here, we chose recently reported high‐performance polymer donors (PM6 & D18‐Fu) and small molecular acceptors (Y6 & L8‐BO) as active layer materials and processed them by different conditions (CN or DIO or none). Based on corresponding 12 groups of device results, and their film morphology characterizations (both ex‐situ and in‐situ ones), the property‐performance relationships are revealed case by case. It is thereby supposed to be taken as a successful attempt to demonstrate the importance and complexity of donor‐acceptor‐additive interaction, since the device performance and physics analyses are also tightly combined with morphology variation. Furthermore, ternary blend construction for PCE improvement provides an approaching 19% level and showcases the potential of understanding‐guided‐optimization (UGO) in the future of OSCs. [ABSTRACT FROM AUTHOR]

Although most polymer/fullerene-based solar cells are cast from a blend of the components in solution, it is also possible to sequentially process the polymer and fullerene layers from quasi-orthogonal solvents. Sequential processing (SqP) not only produces photovoltaic devices with efficiencies comparable to the more traditional bulk heterojunction (BHJ) solar cells produced by blend casting (BC) but also offers the advantage that the polymer and fullerene layers can be optimized separately. In this paper, we explore the morphology produced when sequentially processing polymer/fullerene solar cells and compare it to the BC morphology. We find that increasing polymer regioregularity leads to the opposite effect in SqP and BC BHJ solar cells. We start by constructing a series of SqP and BC solar cells using different types of poly(3-hexylthiophene) (P3HT) that vary in regioregulary and polydispersity combined with [6,6]-phenyl-C61-butyric-acid-methyl-ester (PCBM). We use grazing incidence wide-angle X-ray scattering to demonstrate how strongly changes in the P3HT and PCBM crystallinity upon thermal annealing of SqP and BC BHJ films depend on polymer regioregularity. For SqP devices, low regioregularity P3HT films that possess more amorphous regions allow for more PCBM crystallite growth and thus show better photovoltaic device efficiency. On the other hand, highly regioregular P3HT leads to a more favorable morphology and better device efficiency for BC BHJ films. Comparing the photovoltaic performance and structural characterization indicates that the mechanisms controlling morphology in the active layers are fundamentally different for BHJs formed via SqP and BC. Most importantly, we find that nanoscale morphology in both SqP and BC BHJs can be systematically controlled by tuning the amorphous fraction of polymer in the active layer. © 2014 American Chemical Society.

Polymer:fullerene bulk heterojunction (BHJ) solar cell active layers can be created by traditional blend casting (BC), where the components are mixed together in solution before deposition, or by sequential processing (SqP), where the pure polymer and fullerene materials are cast sequentially from different solutions. Presently, however, the relative merits of SqP as compared to BC are not fully understood because there has yet to be an equivalent (composition- and thickness-matched layer) comparison between the two processing techniques. The main reason why matched SqP and BC devices have not been compared is because the composition of SqP active layers has not been accurately known. In this paper, we present a novel technique for accurately measuring the polymer:fullerene film composition in SqP active layers, which allows us to make the first comparisons between rigorously composition- and thickness-matched BHJ organic solar cells made by SqP and traditional BC. We discover that, in optimal photovoltaic devices, SqP active layers have a very similar composition as their optimized BC counterparts (≈44-50 mass % PCBM). We then present a thorough investigation of the morphological and device properties of thickness- and composition-matched P3HT:PCBM SqP and BC active layers in order to better understand the advantages and drawbacks of both processing approaches. For our matched devices, we find that small-area SqP cells perform better than BC cells due to both superior film quality and enhanced optical absorption from more crystalline P3HT. The enhanced film quality of SqP active layers also results in higher performance and significantly better reproducibility in larger-area devices, indicating that SqP is more amenable to scaling than the traditional BC approach. X-ray diffraction, UV-vis absorption, and energy-filtered transmission electron tomography collectively show that annealed SqP active layers have a finer-scale blend morphology and more crystalline polymer and fullerene domains when compared to equivalently processed BC active layers. Charge extraction by linearly increasing voltage (CELIV) measurements, combined with X-ray photoelectron spectroscopy, also show that the top (nonsubstrate) interface for SqP films is slightly richer in PCBM compared to matched BC active layers. Despite these clear differences in bulk and vertical morphology, transient photovoltage, transient photocurrent, and subgap external quantum efficiency measurements all indicate that the interfacial electronic processes occurring at P3HT:PCBM heterojunctions are essentially identical in matched-annealed SqP and BC active layers, suggesting that device physics are surprisingly robust with respect to the details of the BHJ morphology. © 2014 American Chemical Society.

The two-step layer-by-layer (LBL) deposition of donor and acceptor films enables desired vertical phase separation and high performance in organic solar cells (OSCs), which becomes a promising technology for large-scale printing devices. However, limitations including the use of toxic solvents and unpredictable infiltration between donor and acceptor still hinder the commercial production of LBL OSCs. Herein, we developed a water-based nanoparticle (NP) ink containing donor polymer to construct a mesoscale structure that could be infiltrated with an acceptor solution. Using non-halogen o-xylene for acceptor deposition, the LBL strategy with a mesoscale structure delivered outstanding efficiencies of 18.5% for binary PM6:L8-BObased LBL OSCs. Enhanced charge carrier mobility and restricted trap states were observed in the meso-LBL devices with optimized vertical morphology. It is believed that the findings in this work will bring about more research interest and effort on eco-friendly processing in preparation for the industrial production of OSCs. [ABSTRACT FROM AUTHOR]