Machine learning can be a powerful tool to prescreen new materials, thus accelerating the development of the OPV field.

For organic solar cells to be competitive, the light-absorbing molecules should simultaneously satisfy multiple key requirements, including weak-absorption charge transfer state, high dielectric constant, suitable surface energy, proper crystallinity, etc. However, the systematic design rule in molecules to achieve the abovementioned goals is rarely studied. In this work, guided by theoretical calculation, we present a rational design of non-fullerene acceptor o-BTP-eC9, with distinct photoelectric properties compared to benchmark BTP-eC9. o-BTP-eC9 based device has uplifted charge transfer state, therefore significantly reducing the energy loss by 41 meV and showing excellent power conversion efficiency of 18.7%. Moreover, the new guest acceptor o-BTP-eC9 has excellent miscibility, crystallinity, and energy level compatibility with BTP-eC9, which enables an efficiency of 19.9% (19.5% certified) in PM6:BTP-C9:o-BTP-eC9 based ternary system with enhanced operational stability.

Due to barrierless free charge generation, low charge trapping, and high charge mobilities, the PM6:Y6 organic solar cell (OSC) achieves an excellent power conversion efficiency (PCE) of 15.7%. However, the deficient hole transfer from Y6 to PM6 limits the further enhancement of the device performance. Herein, we demonstrate an additive-induced miscibility and morphology control strategy to achieve the balance of exciton dissociation and charge collection, prompting an increase in the PCE of OSCs composed of PM6:Y6 from 15.7% to 17.5%, which stands as the top PCE value of PM6:Y6 binary OSCs. The external quantum efficiency (EQE) of the optimal device significantly improves in the wavelength range where Y6 harvests photons. Therefore, the short-circuit current density (J_SC) was enhanced to 26.98 mA cm⁻², achieving 94.4% of the maximum theoretical J_SC obtained from the identical device configuration. The remarkable performance enhancement mainly results from the miscibility-driven donor and acceptor phase optimization with hierarchical morphology formation, leading to the improved photon-to-electron response of the Y6 phase, enhanced and balanced charge extraction and collection. Our findings highlight the significance of morphology control towards unleashing the full potential of OSC materials.

Solution processed organic solar cells (OSCs) composed of all small molecules (ASM) are promising for production on an industrial scale owing to the properties of small molecules, such as well-defined chemical structures, high purity of materials, and outstanding repeatability from batch to batch synthesis. Remarkably, ASM OSCs with power conversion efficiency (PCE) beyond 13% were achieved by structure improvement of the electron donor and choosing Y6 as the electron acceptor. However, the fill factor (FF) is an obstacle that limits the further improvement of the PCE for these ASM OSCs. Herein, we focus on the FF improvement of recently reported ASM OSCs with BTR-Cl:Y6 as the active layer by miscibility-induced active layer morphology optimization. The incorporation of fullerene derivatives, which have good miscibility with both BTR-Cl and Y6, results in reduced bimolecular recombination and thus improved FF. In particular, when ca. 5 wt% of PC₇₁BM was added in the active layer, a FF of 77.11% was achieved without sacrificing the open circuit voltage (V_OC) and the short circuit current density (J_SC), leading to a record PCE of 15.34% (certified at 14.7%) for ASM OSCs. We found that the optimized device showed comparable charge extraction, longer charge carrier lifetime, and slower bimolecular recombination rate compared with those of the control devices (w/o fullerene). Our results demonstrate that the miscibility driven regulation of active layer morphology by incorporation of a fullerene derivative delicately optimizes the active layer microstructures and improves the device performance, which brings vibrancy to OSC research.

The lifetime and power conversion efficiency are the key issues for the commercialization of perovskite solar cells (PSCs). In this paper, the development of 2D/3D perovskite hybrids (CA₂PbI₄/MAPbI_xCl_3−x) was firstly demonstrated to be a reliable method to combine their advantages, and provided a new concept for achieving both stable and efficient PSCs through the hybridization of perovskites. 2D/3D perovskite hybrids afforded significantly-improved moisture stability of films and devices without encapsulation in a high humidity of 63 ± 5%, as compared with the 3D perovskite (MAPbI_xCl_3−x). The 2D/3D perovskite-hybrid film did not undergo any degradation after 40 days, while the 3D perovskite decomposed completely under the same conditions after 8 days. The 2D/3D perovskite-hybrid device maintained 54% of the original efficiency after 220 hours, whereas the 3D perovskite device lost all the efficiency within only 50 hours. Moreover, the 2D/3D perovskite hybrid achieved comparable device performances (PCE: 13.86%) to the 3D perovskite (PCE: 13.12%) after the optimization of device fabrication conditions.

A hole transport layer (HTL) plays a key role in efficient hole extraction and transfer in inverted planar perovskite solar cells. A 10–20 nm thick poly (3,4-ethylenedioxythiphene):poly(styrenesulfonate) (PEDOT:PSS) layer is the most popular HTL in such a device structure. But is it essential to construct such a thick PEDOT:PSS layer? To address this question, herein self-assembled PEDOT:PSS monolayers are obtained on the indium tin oxide (ITO) surface through a facile water rinsing process. Perovskite solar cells with water rinsed PEDOT:PSS as a HTL yield improved power conversion efficiency (PCE) from 13.4% to 18.0%, compared with the control cells with as-cast PEDOT:PSS. The main contribution is from the open-circuit voltage (V_oc) and fill factor (FF). Characterization indicates that the majority of PEDOT:PSS is washed away, but an ultra-thin layer of PEDOT:PSS can attach strongly onto ITO via In–O–S chemical bonds between the PSS chain and ITO. Subsequently, PEDOT and PSS form a bilayered structure due to Coulomb interaction. Such an arrangement induces an oriented electric field from positively charged PEDOT to negatively charged PSS, which can accelerate the process of hole extraction. Moreover, the oriented arrangement of PEDOT:PSS monolayers provides higher work function and stronger hydrophobicity, leading to the enhancement in V_oc and stability in the ambient environment. This work suggests that there is still room for the efficiency improvement of perovskite solar cells by optimizing the traditional functional layers.