The printing of large‐area organic solar cells (OSCs) has become a frontier for organic electronics and is also regarded as a critical step in their industrial applications. With the rapid progress in the field of OSCs, the highest power conversion efficiency (PCE) for small‐area devices is approaching 15%, whereas the PCE for large‐area devices has also surpassed 10% in a single cell with an area of ≈1 cm2. Here, the progress of this fast developing area is reviewed, mainly focusing on: 1) material requirements (materials that are able to form efficient thick active layer films for large‐area printing); 2) modular designs (effective designs that can suppress electrical, geometric, optical, and additional losses, leading to a reduction in the PCE of the devices, as a consequence of substrate area expansion); and 3) printing methods (various scalable fabrication techniques that are employed for large‐area fabrication, including knife coating, slot‐die coating, screen printing, inkjet printing, gravure printing, flexographic printing, pad printing, and brush coating). By combining thick‐film material systems with efficient modular designs exhibiting low‐efficiency losses and employing the right printing methods, the fabrication of large‐area OSCs will be successfully realized in the near future.

The high efficiency all-small-molecule organic solar cells (OSCs) normally require optimized morphology in their bulk heterojunction active layers. Herein, a small-molecule donor is designed and synthesized, and single-crystal structural analyses reveal its explicit molecular planarity and compact intermolecular packing. A promising narrow bandgap small-molecule with absorption edge of more than 930 nm along with our home-designed small molecule is selected as electron acceptors. To the best of our knowledge, the binary all-small-molecule OSCs achieve the highest efficiency of 14.34% by optimizing their hierarchical morphologies, in which the donor or acceptor rich domains with size up to ca. 70 nm, and the donor crystals of tens of nanometers, together with the donor-acceptor blending, are proved coexisting in the hierarchical large domain. All-small-molecule photovoltaic system shows its promising for high performance OSCs, and our study is likely to lead to insights in relations between bulk heterojunction structure and photovoltaic performance.

Herein, a simple “Same-A-Strategy” (SAS), constructing p-type and n-type photovoltaic materials with the same electron-accepting (A) unit of benzotriazole, is adopted to initially control the energy offsets. Then, chlorine atoms are introduced into the conjugated side chain of the benzo­[1,2-b:4,5-b′]­dithiophene (BDT) donor unit of the p-type polymer to fine-tune the optoelectronic properties. The chlorinated polymer J52-Cl, blended with a non-fullerene small molecule acceptor BTA3, yields the very small energy offsets (ΔE HOMO = 0.10 eV, ΔE LUMO = 0.28 eV) and the decreased nonradiative recombination loss of 0.24 eV. Benefiting from the strong molecular aggregation, ordered molecular orientation, and fine film morphology, J52-Cl:BTA3 device delivers balanced carriers mobilities and also suppressed charge recombination losses. Consequently, the obtained device yields a very high open-circuit voltage (V OC) of 1.24 V, a short-circuit current (J SC) of 13.16 mA cm–2, and a fill factor of 66.62%, giving rise to a promising power conversion efficiency (PCE) of 10.5%, which is a large breakthrough for organic solar cells with high V OC beyond 1.20 V. Our results provide a rare opportunity to break through the limitation of the problematic trade-off between energy loss and PCE and show a great potential for the application in tandem solar cells.

are mainly due to the higher LUMO of -3.74 eV (ICBA) and -3.72 eV (IC 70 BM) compared with that of PC 61 BM (-3.91 eV). However, further improvement of V oc of P3HT-based organic solar cell by modulation of fullerene is quite difficult and usually leads to the decrease the performance.On the other hand, non-fullerene acceptors have been intensively investigated and some exciting results have been obtained in recent three years, due to their adjustable absorption spectra and energy levels. [5] High PCEs of over 10% have been realized by optimizing both donor materials and nonfullerene acceptors. [6] Furthermore, to combine with classic P3HT donor polymer, electron-deficient building blocks, such as benzothiadiazole (BT), [7] diketopyrrolopyrrole (DPP), [8] perylene diimide, [9] naphthalene diimide, [10] other rylene imide, [11] and other electron-deficient building blocks [12] have been widely adopted to construct non-fullerene acceptors. The V oc and PCE of solar cells based on reported P3HT:non-fullerene small molecule acceptors are summarized in Figure 1. From Figure 1, although many kinds of non-fullerene acceptors were developed, but only five samples could realize a PCE of beyond 4% (typical value for P3HT:PCBM system). In addition, it clearly shows that the V oc could be easily improved to even beyond 1.0 V, but only one sample based on DPP segment could simultaneously achieve a V oc of higher than 1.0 V and a PCE of higher than 4%. [8e] Very recently, the highest PCE of P3HTbased solar cells reached 6.4% with a V oc of 0.8 V by using one BT-containing non-fullerene acceptor. [7f ] Thus, the development of novel non-fullerene acceptor to match well with P3HT is still urgent and necessary for the further application of P3HT-based OSCs.It is well known that benzo[d][1,2,3]triazole (BTA) has the similar chemical structure with BT and BTA-based p-type photovoltaic polymers showed ultra-high PCEs of 7.1%-8.4% and 8.2 BTA-9.5% respectively, when they are combined with fullerene derivatives [13] or non-fullerene acceptors. [14] Comparative to p-type polymers, however, BTA-containing n-type polymers show inferior PCEs of 0.18%-0.4%, [15] and there is also no report of BTA-based non-fullerene small molecule acceptors. In principle, BTA is a weaker electron-withdraw building block than BT, which could up-shift the LUMO energy levels of final materials. Furthermore, the alkyl chain in BTA could also finetune the solubility and crystallinity of final small molecules.Thus, in this communication, we adopted common A 2 A 1 DA 1 A 2 linear molecular structure to design and synthesize the first BTA-containing non-fullerene small molecule acceptor, where rhodanine (R), BTA and indacenodithiophene (IDT) were used as terminal acceptor (A 2 ), bridge acceptor (A 1 ), and central donor (D), respectively. This small molecule, named Organic solar cells (OSCs) have attracted much attention in the last two decades due to their ease of processing, mechanical flexibility, and potential for large-scale low cost fabrication. Afte...

Newly designed asymmetric diketopyrrolopyrrole conjugated polymers with two different aromatic substituents possess a hole mobility of 12.5 cm(2) V(-1) s(-1) in field-effect transistors and a power conversion efficiency of 6.5% in polymer solar cells, when solution processed from a nonchlorinated toluene/diphenyl ether mixed solvent.