Single‐Junction Organic Photovoltaic Cells with Approaching 18% Efficiency

Abstract

Optimizing the molecular structures of organic photovoltaic (OPV) materials is one of the most effective methods to boost power conversion efficiencies (PCEs). For an excellent molecular system with a certain conjugated skeleton, fine tuning the alky chains is of considerable significance to fully explore its photovoltaic potential. In this work, the optimization of alkyl chains is performed on a chlorinated nonfullerene acceptor (NFA) named BTP‐4Cl‐BO (a Y6 derivative) and very impressive photovoltaic parameters in OPV cells are obtained. To get more ordered intermolecular packing, the n‐undecyl is shortened at the edge of BTP‐eC11 to n‐nonyl and n‐heptyl. As a result, the NFAs of BTP‐eC9 and BTP‐eC7 are synthesized. The BTP‐eC7 shows relatively poor solubility and thus limits its application in device fabrication. Fortunately, the BTP‐eC9 possesses good solubility and, at the same time, enhanced electron transport property than BTP‐eC11. Significantly, due to the simultaneously enhanced short‐circuit current density and fill factor, the BTP‐eC9‐based single‐junction OPV cells record a maximum PCE of 17.8% and get a certified value of 17.3%. These results demonstrate that minimizing the alkyl chains to get suitable solubility and enhanced intermolecular packing has a great potential in further improving its photovoltaic performance.

Understanding the Effect of End Group Halogenation in Tuning Miscibility and Morphology of High‐Performance Small Molecular Acceptors

“…[ 1–6 ] Nonfullerene small molecular acceptors (SMAs) [ 7–29 ] are the main driving force for the recent development of the field, with power conversion efficiencies (PCEs) over 17% reported by different teams. [ 30–43 ] SMAs have many attractive properties including their strong and tunable absorption, the easily adjustable energy levels and the enhanced chemical and device stability. Most of these excellent features are enabled by the flexible and feasible synthesis of the SMAs that leads to numerous judiciously designed molecular structures.…”

Enhanced and Balanced Charge Transport Boosting Ternary Solar Cells Over 17% Efficiency

“…[1][2][3][4] Attributed to the rapid progress of tunable nonfullerene acceptors (NFAs) featuring broad absorption and high electron mobility, the power conversion efficiencies (PCEs) of the donor:acceptor bulk heterojunction OSCs have exceeded 17% for single junction cells. [5][6][7][8] To further improve the PCEs, so-called ternary OSCs that integrate two donors and one acceptor or one donor and two acceptors into a photoactive layer, have been established to enhance the light harvesting, while the ternary devices retain the simplicity of fabrication process of the normal binary devices. [9][10][11][12] The PCEs of the OSCs are determined by the three photovoltaic parameters including open-circuit voltage (V oc ), shortcircuit current density (J sc ), and fill factor (FF).…”

Precise Control of Phase Separation Enables 12% Efficiency in All Small Molecule Solar Cells

“…In many cases, σ correlates linearly with the device FF if there is no loss of charge percolation in the mixed domains. [7,10,[32][33][34][39][40][44][45][46] Such correlations need to generally consider scattering contrast from orientation distributions and contrast changes if the texture is changing between samples. [42] Correlation of the meso-scale morphology to device performance is complicated here by the fact that there is significant modulation on length scales larger than the film thickness of 86 nm, as can be clearly observed from the TEM.…”

“…Driven by novel photovoltaic materials and improved device optimization, power conversion efficiencies (PCEs) have recently surpassed 17% for single junction PSCs. [4][5][6][7] Although this value is less than what competing photovoltaic technologies based on silicon or perovskite achieve, the unique attributes of OSCs Compared to conjugated polymers, small-molecule organic semiconductors present negligible batch-to-batch variations, but presently provide comparatively low power conversion efficiencies (PCEs) in small-molecular organic solar cells (SM-OSCs), mainly due to suboptimal nanomorphology. Achieving precise control of the nanomorphology remains challenging.…”

“…The substantial PCE enhancement in recent years mainly originates from the development of new narrow bandgap nonfullerene acceptors (NFAs), which provide broad absorption spectra, energy levels suitable for charge separation, and high electron mobility. [5][6][7][8][9][10][11] NFAs are commonly matched with wide bandgap polymer donors to obtain high efficiency OSCs. [9][10][11] However, due to synthetic complexity, batch-to-batch variations of polymer donors often lead to reduced reproducibility of device performance, hindering the commercialization of OSCs.…”