counterparts and is very attractive for developing semitransparent organic solar cells (ST-OSCs), which have great potential application in building integrated photovoltaic, agricultural greenhouse, car window, and so on. [5,6] Different from opaque device that is concerned mostly with power conversion efficiency (PCE), ST-OSCs also value the transparency in the visible region and adopt average visible transmittance (AVT) to assess their see-through function. [7] However, there is a trade-off relationship between the see-through function and photovoltaic performances since enhancing the light transmission generally leads to lower amount of photons to be utilized. Therefore, efforts including material designing and device engineering are widely employed to reconcile the intrinsic contradiction between AVT and PCE. [8][9][10][11][12][13][14][15][16] Ideally, the photon-absorbing materials in ST-OSCs should have the main absorption in the NIR region and weak absorption in the visible region. [17] Previously, various narrow bandgap polymer donors were synthesized and matched with fullerene acceptors in ST-OSCs. [18,19] Recently, with the aid of advances in materials designing of NIR-absorbing non-fullerene electron acceptors, the PCEs of ST-OSCs have already surpassed 14%. [20,21] Meanwhile, optical engineering technologies, including photonic crystals, [22,23] antireflective device structures, [24,25] or optical microcavity structures, [26,27] have been applied to improve the PCEs and optimize the transmission spectra with deliberately designed layout but energy-consuming process. Other strategies, including multi-component, [28,29] sequentially deposited active layer [30,31] and thickness optimization [20] are also implemented to regulate photon harvesting range and improve PCEs in these fields.More directly, lowering the large-bandgap donor content in bulk-heterojunction (BHJ) has been demonstrated as a facile strategy to tune the transmittance spectrum of active layer. [32][33][34] The AVTs of D18-Cl:Y6-1O films have been continuously changed from 30.3% to 68.0% through ranging the donor and acceptor weight ratio (D:A ratio) from 1.1:1.6 to 0.1:1.6. [4] These previous works imply the feasibility of achieving high AVT from low-donor content ST-OSCs. Nevertheless, the performance optimization of OSCs with dilute donors still remains a challenge, mainly originating from the imbalanced charge Semitransparent organic solar cells (ST-OSCs) have promising prospects for building or vehicle integrated solar energy harvesting with energy generation and see-through function. How to achieve both an adequate average visible transmittance (AVT) and high-power conversion efficiency (PCE) is always the key issue. Herein, a simple but effective strategy for constructing high performance ST-OSCs by introducing a small molecule [2-(9-H-Carbazol-9-yl) ethyl] phosphonic acid (2PACz) into a low-donor content active layer is reported. The fill factor is improved from 70.5% to 75.5% and correlated to the mitigated charge recombination a...
Although much research on device engineering have brought about significant improvements in PM6:Y6-based polymer solar cell (PSCs) performance, there is still a lack of relevant research to solve the problems caused by the over-aggregation of Y6 and the long-term stability of the device morphology. Herein, a newly designed and synthesized low-bandgap asymmetric small molecule acceptor TIT-2Cl based on thieno[3,2-b]indole core is elaborately introduced into PM6:Y6-based PSCs to suppress the over-aggregation of Y6 molecules with significantly increased efficiency from 15.78% to 17.00%. Moreover, the addition of TIT-2Cl contributes to improved light harvesting, the lowest unoccupied molecular orbital level of Y6:TIT-2Cl, charge separation, transport, and extraction. Simultaneously, the PSCs are further prepared by using the progressive spin-coating method of layer-by-layer (LBL). Due to the formation of vertical phase distribution and the improvement of carrier transport performance, the champion efficiency of LBL-type ternary PSCs reaches 18.18%, which is the highest efficiency reported for PM6:Y6-based PSCs, along with superior stability and compositional insensitivity. Therefore, the results show that the combination of ternary strategy by incorporating appropriate asymmetric molecules and the LBL method is an effective means to fabricate highly efficient stable PSCs.
Incorporating solvent additives in donor and acceptor solutions has been considered as effective strategy in reaching efficient organic solar cells. As the state-of-the-art photovoltaic materials have thiophene sequences along their...
A ternary strategy is viable to minimize the trade-off between short-circuit current density (J sc ) and open-circuit voltage (V oc ) in organic solar cells. Generally, the ternary OSCs can achieve a higher PCE than the binary counterparts by subtly utilizing the particular photoelectric properties of the third material. In this regard, we choose BTP-CC with a higher-lying LUMO level based on a fused TPBT (dithienothiophen[3.2-b]-pyrrolobenzothiadiazole) central framework and CC (2-(6-oxo-5,6-dihydro-4H-cyclopenta [b]thiophen-4-ylidene) malononitrile) flanking groups as the third component to broaden the light-absorption spectrum, regulate the bulk heterojunction (BHJ) morphology, improve the V oc , and reduce the charge recombination in OSCs. In addition, BTP-CC demonstrates intense intermolecular energy transfer to Y6 by fluorescence resonance energy transfer (FRET) pathway, which is due to the photoluminescence (PL) spectrum of BTP-CC covering the absorption region of Y6. The PM6:Y6:BTP-CC based ternary OSC achieves a champion PCE of 17.55%. Further investigation indicates that introduction of BTP-CC could reduce the trap states in OSCs, leading to an increased charge carrier density. Moreover, the incorporation of BTP-CC could improve the device stability. These results demonstrated that BTP-CC is important in improving the photovoltaic performance of ternary OSCs, and this work also provides a guideline for constructing ideal ternary OSCs in the future.
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