Broadening the optical absorption of organic photovoltaic (OPV) materials by enhancing the intramolecular push-pull effect is a general and effective method to improve the power conversion efficiencies of OPV cells. However, in terms of the electron acceptors, the most common molecular design strategy of halogenation usually results in down-shifted molecular energy levels, thereby leading to decreased open-circuit voltages in the devices. Herein, we report a chlorinated non-fullerene acceptor, which exhibits an extended optical absorption and meanwhile displays a higher voltage than its fluorinated counterpart in the devices. This unexpected phenomenon can be ascribed to the reduced non-radiative energy loss (0.206 eV). Due to the simultaneously improved short-circuit current density and open-circuit voltage, a high efficiency of 16.5% is achieved. This study demonstrates that finely tuning the OPV materials to reduce the bandgap-voltage offset has great potential for boosting the efficiency.

Fabricating organic solar cells (OSCs) with a tandem structure has been considered an effective method to overcome the limited light absorption spectra of organic photovoltaic materials. Currently, the most efficient tandem OSCs are fabricated by adopting fullerene derivatives as acceptors. In this work, we designed a new non-fullerene acceptor with an optical band gap (E) of 1.68 eV for the front subcells and optimized the phase-separation morphology of a fullerene-free active layer with an E of 1.36 eV to fabricate the rear subcell. The two subcells show a low energy loss and high external quantum efficiency, and their photoresponse spectra are complementary. In addition, an interconnection layer (ICL) composed of ZnO and a pH-neutral self-doped conductive polymer, PCP-Na, with high light transmittance in the near-IR range was developed. From the highly optimized subcells and ICL, solution-processed fullerene-free tandem OSCs with an average power conversion efficiency (PCE) greater than 13% were obtained.

A naphthalene diimide (NDI)-based organic molecule (NDI-N) was prepared to be used as printable cathode interlayer (CIL) for organic solar cells (OSCs). NDI-N possesses combined advantages of high crystallinity and good film-forming properties, endowing the material with excellent electron-transport properties and good processability. NDI-N can be processed by printing methods; in this case an OSC device of 1 cm 2 was fabricated by using blade-coated NDI-N and an efficiency of 13.2% was achieved, which represents the highest efficiency to date for large-area OSCs.

Synergistic optimization of donor-acceptor blend morphologyis a hurdle in the path of realizing efficient non-fullerene small-molecule organic solar cells (NFSM-OSCs) due to the anisotropic conjugated backbones of both donor and acceptor. Therefore, developing a facile molecular design strategy to effectively regulate the crystalline properties of photoactive materials, and thus, enable the optimization of blend morphology is of vital importance. In this study, a new donor molecule B1, comprising phenyl-substituted benzodithiophene (BDT) central unit, exhibits strong interaction with the non-fullerene acceptor BO-4Cl in comparison with its corresponding thiophene-substituted BDT-based material, BTR. As a result, the B1 is affected and induced from an edgeon to a face-on orientation by the acceptor, while the BTR and the acceptor behave individually for the similar molecular orientation in pristine and blend films according to grazing incidence wide angle X-ray scattering results. It means the donor-acceptor blend morphology is synergistically optimized in the B1 system, and the B1:BO-4Cl-based devices achieve an outstanding power conversion efficiency (PCE) of 15.3%, further certified to be 15.1% by the National Institute of Metrology, China. Our results demonstrate a simple and effective strategy to improve the crystalline properties of the donor molecule as well as synergistically optimize the morphology of the all-small-molecule system, leading to the high-performance NFSM-OSCs.

Revealing the charge generation is a crucial step to understand the organic photovoltaics. Recent development in non‐fullerene organic solar cells (OSCs) indicates efficient charge separation even with negligible energetic offset between the donor and acceptor materials. These new findings trigger a critical question concerning the charge separation mechanism in OSCs, traditionally believed to result from sufficient energetic offset between the polymer donor and fullerene acceptor. We propose a new mechanism, which involves the molecular electrostatic potential, to explain efficient charge separation in non‐fullerene OSCs. Together with the new mechanism, we demonstrate a record efficiency of ~12% for systems with negligible energetic offset between donor and acceptor materials. Our analysis also rationalizes different requirement of the energetic offset between fullerene‐based and non‐fullerene OSCs, and paves the way for further design of OSC materials with both high photocurrent and high photovoltage at the same time.

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Two wide band gap polymer donors were developed for fullerene-free polymer solar cells. The photovoltaic performance of the PB3T:IT-M device processed by anisole achieved a high PCE of 11.9%.

With the rapid advance of organic photovoltaic materials, the energy level structure, active layer morphology, and fabrication procedure of organic solar cells (OSCs) are changed significantly. Thus, the photoelectronic properties of many traditional electrode interlayers have become unsuitable for modifying new active layers; this limits the further enhancement in OSC efficiencies. Herein, a new design strategy of tailoring the end‐capping unit, ITIC, to develop a cathode interlayer (CIL) material for achieving high power conversion efficiency (PCE) in OSCs is demonstrated. The excellent electron accepting capacity, suitable energy level, and good film‐forming ability endow the S‐3 molecule with an outstanding electron extraction property. A device with S‐3 shows a PCE of 16.6%, which is among the top values in the field of OSCs. More importantly, it is demonstrated that the electrostatic potential difference between the CIL molecule and the polymer donor plays a crucial role in promoting exciton dissociation at the CIL/active layer interface, contributing to additional charge generation; this is crucial for enhancement of the current density. The results of this work not only develop a new design strategy for high‐performance CIL, but also demonstrate a reliable approach of density functional theory (DFT) calculation to predict the effect of the CIL chemical structure on exciton dissociation in OSCs.