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Achieving an ideal morphology to realize efficient charge generation and transport is an imperative avenue to improve the photovoltaic performance of all small‐molecule organic solar cells (SM‐OSCs). Here, ternary SM‐OSCs are fabricated based on a new small molecule donor, SM‐mB, and an alloyed blend acceptor of Y6 and its derivative, L8‐BO, and desirable hierarchical morphology with appropriate nanoscale phase separation is successfully realized through adjusting the thermal annealing treatment conditions and compositions of mixed acceptors in the active layer. Then the ternary SM‐OSCs achieve an excellent PCE of 17.06 %, which is one of the best results for the SM‐OSCs so far. The desirable morphology can be ascribed to the optimization of the miscibility‐driven donor and acceptor blend morphology that takes full advantage of the individual advantages of both acceptors, which facilitate efficient charge generation and extraction with more balanced charge carrier mobilities. More importantly, the photovoltaic performance of the ternary SM‐OSCs possesses a high tolerance to the device fabrication conditions, including thermal annealing treatment, and is insensitive to film thickness, which is beneficial for large‐area manufacture and future practical applications. [ABSTRACT FROM AUTHOR]

High efficiency organic solar cells (OSCs) based on A‐DA′D‐A type small molecule acceptors (SMAs) were mostly fabricated by toxic halogenated solvent processing, and power conversion efficiency (PCE) of the non‐halogenated solvent processed OSCs is mainly restricted by the excessive aggregation of the SMAs. To address this issue, we developed two vinyl π‐spacer linking‐site isomerized giant molecule acceptors (GMAs) with the π‐spacer linking on the inner carbon (EV‐i) or out carbon (EV‐o) of benzene end group of the SMA with longer alkyl side chains (ECOD) for the capability of non‐halogenated solvent‐processing. Interestingly, EV‐i possesses a twisted molecular structure but enhanced conjugation, while EV‐o shows a better planar molecular structure but weakened conjugation. The OSC with EV‐i as acceptor processed by the non‐halogenated solvent o‐xylene (o‐XY) demonstrated a higher PCE of 18.27 % than that of the devices based on the acceptor of ECOD (16.40 %) or EV‐o (2.50 %). 18.27 % is one of the highest PCEs among the OSCs fabricated from non‐halogenated solvents so far, benefitted from the suitable twisted structure, stronger absorbance and high charge carrier mobility of EV‐i. The results indicate that the GMAs with suitable linking site would be the excellent candidates for fabricating high performance OSCs processed by non‐halogenated solvents. [ABSTRACT FROM AUTHOR]

Reducing the energy loss of sub-cells is critical for high performance tandem organic solar cells, while it is limited by the severe non-radiative voltage loss via the formation of non-emissive triplet excitons. Herein, we develop an ultra-narrow bandgap acceptor BTPSeV-4F through replacement of terminal thiophene by selenophene in the central fused ring of BTPSV-4F, for constructing efficient tandem organic solar cells. The selenophene substitution further decrease the optical bandgap of BTPSV-4F to 1.17 eV and suppress the formation of triplet exciton in the BTPSV-4F-based devices. The organic solar cells with BTPSeV-4F as acceptor demonstrate a higher power conversion efficiency of 14.2% with a record high short-circuit current density of 30.1 mA cm−2 and low energy loss of 0.55 eV benefitted from the low non-radiative energy loss due to the suppression of triplet exciton formation. We also develop a high-performance medium bandgap acceptor O1-Br for front cells. By integrating the PM6:O1-Br based front cells with the PTB7-Th:BTPSeV-4F based rear cells, the tandem organic solar cell demonstrates a power conversion efficiency of 19%. The results indicate that the suppression of triplet excitons formation in the near-infrared-absorbing acceptor by molecular design is an effective way to improve the photovoltaic performance of the tandem organic solar cells. Reducing energy loss of sub-cells is critical for high performance tandem organic solar cells. Here, the authors design and synthesize an ultra-narrow bandgap acceptor through replacement of terminal thiophene by selenophene in the central fused ring, achieving efficiency of 19% for tandem cells. [ABSTRACT FROM AUTHOR]

Tandem organic solar cell (TOSC), composed of the front and rear cells with complementary absorption, is effective device structure for surpassing the Shockley–Queisser limit of single‐junction organic solar cells (OSCs). However, most of the medium bandgap (≈1.6 eV) organic photovoltaic materials for front cells in the TOSCs show considerable voltage losses. In this work, two medium bandgap (1.63 eV) isomeric small molecule acceptors m‐DTC‐Cl‐1 and m‐DTC‐Cl‐2 are synthesized with different chlorine substitution positions in 2‐(3‐oxo‐2,3‐dihydroinden‐1‐ylidene)malononitrile (IC). The different chlorine substituted positions in IC groups show significant influences on the physicochemical properties, charge dynamics, morphology, and photovoltaic performance of the acceptors. Consequently, the OSC with PTO2 as polymer donor and m‐DTC‐Cl‐2 as acceptor delivers a champion power conversion efficiency (PCE) of 14.1% with a high open circuit voltage of 1.05 V and a low nonradiative energy loss of 0.25 eV, which indicates that the OSC is an ideal candidate for the application as front cell in the TOSCs. Then, a monolithic TOSC is fabricated with the OSC based on PTO2:m‐DTC‐Cl‐2 as front cell and the OSC based on PTB7‐Th:BTPV‐4Cl as rear cell, which demonstrates a high PCE of 18.8%. [ABSTRACT FROM AUTHOR]

All-polymer solar cells (all-PSCs) based on polymerized small molecular acceptors (PSMAs) have made significant progress recently. Here, we synthesize two A-DA'D-A small molecule acceptor based PSMAs of PS-Se with benzo[c][1,2,5]thiadiazole A'-core and PN-Se with benzotriazole A'-core, for the studies of the effect of molecular structure on the photovoltaic performance of the PSMAs. The two PSMAs possess broad absorption with PN-Se showing more red-shifted absorption than PS-Se and suitable electronic energy levels for the application as polymer acceptors in the all-PSCs with PBDB-T as polymer donor. Cryogenic transmission electron microscopy visualizes the aggregation behavior of the PBDB-T donor and the PSMA in their solutions. In addition, a bicontinuous-interpenetrating network in the PBDB-T:PN-Se blend film with aggregation size of 10~20 nm is clearly observed by the photoinduced force microscopy. The desirable morphology of the PBDB-T:PN-Se active layer leads its all-PSC showing higher power conversion efficiency of 16.16%. Through development of non-fullerene acceptors, OPVs have reached efficiencies of 18%, yet the inadequate operational lifetime still poses a challenge for the commercialisation. Here, the authors investigate the origin of instability of NFA solar cells, and propose some strategies to mitigate this issue. [ABSTRACT FROM AUTHOR]

Organic solar cells (OSCs) have recently reached a remarkably high efficiency and become a promising technology for commercial application. However, OSCs with top efficiency are mostly processed by halogenated solvents and with additives that are not environmentally friendly, which hinders large‐scale manufacture. In this study, high‐performance tandem OSCs, based on polymer donors and two small‐molecule acceptors with different bandgaps, are fabricated by solution processing with non‐halogenated solvents without additive. Importantly, the two active layers developed from non‐halogenated solvents show better phase segregation and charge transport properties, leading to superior performance than halogenated ones. As a result, a tandem OSC with high efficiency of up to 16.67% is obtained, showing unique advantages in future massive production. [ABSTRACT FROM AUTHOR]

Tandem organic solar cells are based on the device structure monolithically connecting two solar cells to broaden overall absorption spectrum and utilize the photon energy more efficiently. Herein, we demonstrate a simple strategy of inserting a double bond between the central core and end groups of the small molecule acceptor Y6 to extend its conjugation length and absorption range. As a result, a new narrow bandgap acceptor BTPV-4F was synthesized with an optical bandgap of 1.21 eV. The single-junction devices based on BTPV-4F as acceptor achieved a power conversion efficiency of over 13.4% with a high short-circuit current density of 28.9 mA cm−2. With adopting BTPV-4F as the rear cell acceptor material, the resulting tandem devices reached a high power conversion efficiency of over 16.4% with good photostability. The results indicate that BTPV-4F is an efficient infrared-absorbing narrow bandgap acceptor and has great potential to be applied into tandem organic solar cells. Development of tandem organic solar cells has been limited by the choice of near-infrared absorbing materials for the rear cell. Here, the authors report a simple strategy to extend the conjugation length of acceptor Y6 and broaden its absorption range to near-infrared region. A tandem organic solar cell with efficiency of 16.4% was achieved. [ABSTRACT FROM AUTHOR]

We synthesize a new quinoxaline-based polymer donor PBQ8 with n -octyl side chain on the quinoxaline unit, which possesses the same skeleton structure to the previously reported PBQ5 (with isooctyl side chain). When blending with polymer acceptor PY-IT, the PBQ8:PY-IT based devices demonstrated a higher PCE value of 17.04%, which is one of the highest PCEs occurred in the all-PSCs. [Display omitted] Recently, the power conversion efficiencies (PCEs) of all-polymer solar cells (all-PSCs) have increased rapidly. To further increase the PCE of all-PSCs, it is necessary to create new donor polymers matching the polymer acceptors. In this paper, we synthesize a new quinoxaline-based polymer donor PBQ8 with n -octyl side chain on the quinoxaline unit, which possesses the same skeleton structure to the previously reported PBQ5 (with isooctyl side chain). The effects of alkyl side chains on the physicochemical properties of the polymer donor were investigated. In comparison with PBQ5, PBQ8 exhibits stronger intermolecular interactions and better molecular packing. When blending with polymer acceptor PY-IT, the PBQ8:PY-IT based devices demonstrated a higher PCE value of 17.04%, which is one of the highest PCEs occurred in the all-PSCs. And the PBQ5:PY-IT (PCE 15.56%, V oc 0.907 V, FF 69.72%, and J sc 24.60 mA cm−2) is much lower. The PBQ8:PY-IT blend displayed more efficient exciton dissociation, better molecular stacking properties, preferable phase separation and higher mobility. These indicate that as an effective method, side chain engineering can improve the efficiency of the all-PSCs. [ABSTRACT FROM AUTHOR]