Morphology of the donor: acceptor blend plays a critical role in the photovoltaic performance of the organic solar cells (OSCs). Herein, liquid-phase-exfoliated black phosphorus nanoflakes (BPNFs), for their outstanding electronic property and good compatibility to solution process, were applied to fullerene-free OSCs as morphology modifier. Revealed by X-ray scattering measurements, the PTB7-Th: IEICO-4F blends incorporated with BPNFs exhibit more ordered π-π stacking and promoted domain purity, contributing to lower charge transport resistance and suppressed charge recombination within the bulk heterojunction (BHJ). As a result, a high fill factor (FF) of 0.73 and a best power conversion efficiency (PCE) of 12.2% were obtained for fullerene-free OSCs based on PTB7-Th: IEICO-4F blends incorporating with BPNFs, which is among the highest FF of the as-cast fullerene-free OSCs with PCE over 12%. More importantly, the embedded BPNFs help to improve the morphological stability of the devices probably by retarding the phase mixing in the BHJ during the aging period. Besides, analogous enhancements were observed in another fullerene-free OSCs based on PBDB-T: ITIC. In a word, this work provides a new strategy of using two-dimentional nanoflakes as facile and universal morphology modifier for efficient fullerene-free OSCs.

The ternary strategy for incorporating multiple photon-sensitive components into a single junction has emerged as an effective method for optimizing the nanoscale morphology and improving the device performance of organic solar cells (OSCs). In this study, efficient and stable ternary OSCs were achieved by introducing the small-molecule dye (5E, 5'E)-5, 5'-(4', 4"-(1, 2-diphenylethene-1, 2-diyl)bis(biphenyl-4', 4-diyl))bis(methan-1-yl-1-ylidene)bis(3-ethyl-2-thioxothia zolidin-4-one) (BTPE-Rn) into poly[4, 8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1, 2-b: 4, 5-b']dithiophene-co-3-fluorothieno[3, 4-b]thiophene-2-carboxylate] (PTB7-Th): [6, 6]-phenyl C₇₁ butyric acid methyl ester (PC₇₁BM) blend films processed using a 1, 8-diiodooctane (DIO)-free solvent. The incorporation of BTPE-Rn enhanced the short-circuit current density and fill factor of the ternary OSCs compared with those of binary OSCs. An investigation of the optical, electronic, and morphological properties of the ternary blends indicated that the third component of BTPE-Rn not only promoted the photon utilization of blends through the energy-transfer process but also improved the electron mobility of the blends owing to the fullerene-rich nanophase optimization. More importantly, this ternary strategy of utilizing a small-molecule dye to replace the photounstable DIO additive enhanced the operational stability of the OSCs.

We systematically investigated the development of film morphology and crystallinity of methyl-ammonium bismuth (III) iodide (MA₃Bi₂I₉) through onestep spin-coating on TiO₂-deposited indium tin oxide (ITO)/glass. The precursor solution concentration and substrate structure have been demonstrated to be critically important in the active-layer evolution of the MA₃Bi₂I₉-based solar cell. This work successfully improved the cell efficiency to 0.42% (average: 0.38%) with the mesoscopic architecture of ITO/compact-TiO₂/mesoscopic-TiO₂ (meso-TiO₂)/MA₃Bi₂I₉/2, 2′, 7, 7′-tetrakis(N, N-di-4-methoxyphenylamino)-9, 9′spiro-bifluorene (spiro-MeOTAD)/MoO₃/Ag under a precursor concentration of 0.45 M, which provided the probability of further improving the efficiency of the Bi³⁺-based lead-free organic–inorganic hybrid solar cells.