A new electron-rich central building block, 5,5,12,12-tetrakis(4-hexylphenyl)-indacenobis-(dithieno[3,2-b:2',3'-d]pyrrol) (INP), and two derivative nonfullerene acceptors (INPIC and INPIC-4F) are designed and synthesized. The two molecules reveal broad (600-900 nm) and strong absorption due to the satisfactory electron-donating ability of INP. Compared with its counterpart INPIC, fluorinated nonfullerene acceptor INPIC-4F exhibits a stronger near-infrared absorption with a narrower optical bandgap of 1.39 eV, an improved crystallinity with higher electron mobility, and down-shifted highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels. Organic solar cells (OSCs) based on INPIC-4F exhibit a high power conversion efficiency (PCE) of 13.13% and a relatively low energy loss of 0.54 eV, which is among the highest efficiencies reported for binary OSCs in the literature. The results demonstrate the great potential of the new INP as an electron-donating building block for constructing high-performance nonfullerene acceptors for OSCs.

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Dopant‐free hole transport materials (HTMs) are essential for commercialization of perovskite solar cells (PSCs). However, power conversion efficiencies (PCEs) of the state‐of‐the‐art PSCs with small molecule dopant‐free HTMs are below 20%. Herein, a simple dithieno[3,2‐b:2′,3′‐d]pyrrol‐cored small molecule, DTP‐C6Th, is reported as a promising dopant‐free HTM. Compared with commonly used spiro‐OMeTAD, DTP‐C6Th exhibits a similar energy level, a better hole mobility of 4.18 × 10−4 cm2 V−1 s−1, and more efficient hole extraction, enabling efficient and stable PSCs with a dopant‐free HTM. With the addition of an ultrathin poly(methyl methacrylate) passivation layer and properly tuning the composition of the perovskite absorber layer, a champion PCE of 21.04% is achieved, which is the highest value for small molecule dopant‐free HTM based PSCs to date. Additionally, PSCs using the DTP‐C6Th HTM exhibit significantly improved long‐term stability compared with the conventional cells with the metal additive doped spiro‐OMeTAD HTM. Therefore, this work provides a new candidate and effective device engineering strategy for achieving high PCEs with dopant‐free HTMs.

In this work, sidechain engineering on conjugated fused-ring acceptors for conformation locking has been demonstrated as an effective molecular design strategy for high-performance nonfullerene organic solar cells (OSCs). A novel non-fullerene acceptor (ITC6-IC) was designed and developed by introducing long alkyl chains into the terminal electron-donating building blocks. ITC6-IC achieved definite conformation with a planar structure and better solubility in common organic solvents. The weak electron-donating hexyl incurs the upshift LUMO level of ITC6-IC, resulting in a higher V OC in comparison to the widely used ITIC. The OSCs based on PBDB-T:ITC6-IC revealed a promising PCE of 11.61 % and an expected high V OC of 0.97 V. The weaker π-π stacking induced by steric hindrance affords ITC6-IC with enhanced compatibility with polymer donors. The blend film treated with suitable thermal annealing exhibits a fibril crystallization feature with a good bicontinuous network morphology. Our results indicate the molecular design approach of ITC6-IC can be inspirational for future development of non-fullerene acceptors for high efficiency OSCs.In terms of high performance bulk heterojunction (BHJ) organic solar cells (OSCs), [1][2][3][4] various small-molecule acceptors (SMAs) have been explored as promising alternatives to the fullerene derivatives. [5][6][7][8][9][10][11][12][13][14] Non-fullerene SMAs have drawn increasing attention and developed rapidly in past