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We synthesize and compare four near-infrared absorbing fused-ring electron acceptors named as nTTIC (n=2, 3, 4, and 5), based on different number of thieno[3,2-b]thiophene (TT) unit as the electron-donating core. With increasing the TT unit, absorption spectrum of the TTIC series red shifts, and the highest occupied molecular orbital (HOMO) upshifts notably. It is worth noting that 4TTIC and 5TTIC exhibit absorption edges approaching 1100 nm, which is the photoresponse limit of solar cells based on crystal silicon. When the TTIC series acceptors are blended with polymer donor PM6, the binary-blend organic solar cells based on 3TTIC show the best power conversion efficiency (PCE) of 13.1%. In contrast, 2TTIC-based devices exhibit relatively lower PCE of 8.32%, mainly caused by the larger energy loss and blue-shifted absorption. Due to insufficient driving force of charge separation caused by very high HOMO, 4TTIC and 5TTIC show poor PCEs lower than 3%. [ABSTRACT FROM AUTHOR]

Surface defect modulation utilizing Fused-ring electron acceptor molecules achieved a dramatically enhanced open-circuit voltage from 1.079 V to 1.278 V and a record efficiency up to 3.31% for double Cs 2 AgBiBr 6 perovskite solar cells. [Display omitted] • Fused-ring acceptors were used to passivate Cs 2 AgBiBr 6 perovskite. • Nonradiative recombination was suppressed by passivating Ag-exposed surface defects. • The modified double PSCs achieved a record efficiency of 3.31%. • Excellent long-term light-heat stabilities were achieved, with > 97% PCE sustained. Lead-free double perovskites have drawn increasing attention for addressing the stability and toxicity challenges from lead-based halide perovskites. However, their power conversion efficiencies (PCE) are still far behind that of Pb-based perovskite solar cells (PSCs) mainly because of the severe energy loss. Herein, we successfully employed the fused-ring electron acceptor (FREA) molecules to passivate defects in Cs 2 AgBiBr 6 -based double PSCs to realize a dramatically enhanced open-circuit voltage (V OC) from 1.079 V to 1.278 V and a champion PCE up to 3.31%, which is the highest efficiency for double PSCs to date. The strong binding of C≡N and N=C–S groups on FREA with Ag-exposed surface of Cs 2 AgBiBr 6 effectively decreased surface trap densities and considerably suppressed non-radiative recombination. Moreover, the passivated devices showed superior long-term stability, which maintained 98.5% and 97.2% of the initial efficiency under continuous AM 1.5 G illumination and 85 ℃ heating for 300 h, respectively. This work manifests the importance of the rational design of functional passivation molecules to improve the performance and stability of double PSCs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Efficient PBDB-T ternary solar cells using two alloy-forming acceptors with distinct structural orders. • Förster resonance energy transfer between two acceptors; • Optimal phase-separation and structural order achieved with less crystalline third component; • A champion PCE of 14.55% for PBDB-T single-junction solar cells. Ternary organic solar cells (OSCs) have demonstrated great potential in boosting the power conversion efficiencies (PCEs) of single-junction devices. Screening suitable third component is crucial but challenging for different host binary OSCs. We report herein an efficient ternary strategy in achieving highly efficient PBDB-T based devices by incorporating two alloy-forming fused-ring electron acceptors (FREAs) with distinct structural orders. INPIC-Si as the third component showcases a relatively narrower bandgap and higher energy levels than the host acceptor IDTO-T-4F. Featuring good compatibility and alloy-forming blends, two FREAs generate Förster resonance energy transfer from IDTO-T-4F to INPIC-Si, facilitating efficient exciton dissociation and charge carrier transport. Importantly, the low crystalline INPIC-Si decreases the strong aggregation of PBDB‐T:IDTO-T-4F blends for optimal phase-separation and structural order. Consequently, the best PBDB‐T:IDTO-T-4F:INPIC-Si ternary OSCs deliver a champion PCE of 14.55% with simultaneously improved device parameters over binary ones. To the best of our knowledge, this performance is among the highest for PBDB-T-based ternary OSCs in literature. Our work demonstrates the incorporation of a narrow bandgap FREA with low structural order into heavily aggregated binary blends can optimize the blend morphology for reduced energy loss and significantly improved photovoltaic performance in ternary OSCs. [ABSTRACT FROM AUTHOR]