Currently, nearly all high‐efficiency organic photovoltaic devices use donor polymers based on the benzo‐dithiophene (BDT) unit. To diversify the choices of building blocks for high‐performance donor polymers, the use of benzo‐difuran (BDF) units is explored, which can achieve reduced steric hindrance, stronger molecular packing, and tunable energy levels. In previous research, the performance of BDF‐based devices lagged behind those of BDT‐based devices. In this study, a high efficiency (18.4%) is achieved using a BDF‐based polymer donor, which is the highest efficiency reported for BDF donor materials to date. The high efficiency is enabled by a donor polymer (D18‐Fu) and the aid of a solid additive (2‐chloronaphthalene), which is the isomer of the commonly used additive 1‐chloronaphthalene. These results revealed the significant effect of 2‐chloronaphthalene in optimizing the morphology and enhancing the device parameters. This work not only provides a new building block that can achieve an efficiency comparable to dominant BDT units but also proposes a new solid additive that can replace the widely used 1‐chloronaphthalene additive.
All-polymer solar cells (All-PSCs), whose electron donor and acceptors are both polymeric materials, have attracted great research attention in the past few years. However, most all-PSC devices with top-of-the-line efficiencies are processed from chloroform. In this work, we apply the sequential processing (SqP) method to fabricate All-PSCs from an aromatic hydrocarbon solvent, toluene, and obtain efficiencies up to 17.0%. By conducting a series of characterizations on our films and devices, we demonstrate that the preparation of SqP devices using toluene can effectively reduce carrier recombination, enhance carrier mobility and promote the fill factor of the device.
Adding a small‐molecule donor (SMD) to state‐of‐the‐art nonfullerene organic solar cells (OSCs) is demonstrated as a useful strategy to construct ternary organic solar cells, as SMDs typically have high crystallinity and can tune charge transport properties of OSCs. However, the absorption of most SMDs overlaps with typical donor polymers (e.g., PM6), which is against the general guidelines of adopting materials with complementary absorption in ternary OSCs. Herein, the absorption of state‐of‐art SMDs (BTR‐Cl) by linking the beta position of the outer thiophene to the alpha position of the inner thiophene unit is intentionally blueshifted. The resulting molecule β‐S1 shows a maximum absorption peak at 505 nm in the film state, which exhibits wider bandgap and shows complementary absorption with the host system (PM6:Y6). The corresponding ternary OSCs with 20%wt β‐S1 show significantly enhanced efficiency from 16.2% to 17.1% due to the increased short‐circuit current (J
SC) and improved fill factor (FF). Herein, an effective strategy to design SMDs with both wider bandgaps and higher crystallinity for high‐performance ternary OSCs is presented.
All-polymer solar cells (all-PSCs) are organic solar cells in which both the electron donor and the acceptor are polymers and are considered more promising in large-scale production. Thanks to the polymerizing small molecule acceptor strategy, the power conversion efficiency of all-PSCs has ushered in a leap in recent years. However, due to the electrical properties of polymerized small-molecule acceptors (PSMAs), the FF of the devices is generally not high. The typical electron transport material widely used in these devices is PNDIT-F3N, and it is a common strategy to improve the device fill factor (FF) through interface engineering. This work improves the efficiency of all-polymer solar cells through interfacial layer engineering. Using PDINN as the electron transport layer, we boost the FF of the devices from 69.21% to 72.05% and the power conversion efficiency (PCE) from 15.47% to 16.41%. This is the highest efficiency for a PY-IT-based binary all-polymer solar cell. This improvement is demonstrated in different all-polymer material systems.
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