Suchergebnisse

Developing near infrared (NIR) organic semiconductors is indispensable for promoting the performance of organic solar cells (OSCs), but addressing the trade-off between voltage and current density thus achieving high efficiency with low energy loss is still an urgent challenge. Herein, NIR acceptors (H1, H2 and H3) with a photoresponse beyond 1000 nm were developed by conjugating dithienopyrrolobenzothiadiazole to 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrileviavaried alkyl thiophene bridges. It was found that the linear outward chains in thiophene bridges could mitigate both the conformation disorder of H3 and the electronic disorder of the PBDB-T:H3 blends, which could help to form a favorable blend morphology, facilitating highly efficient photoelectric conversion in the resultant OSCs. As a result, devices based on PBDB-T:H3 achieve a high efficiency of 13.75% with a low energy loss of 0.55 eV, which is one of the highest efficiencies and the lowest energy loss among OSCs with an optoelectronic response near 1000 nm. This work provides a new design strategy towards NIR acceptors for efficient OSCs and future exploration of functional optoelectronics. ; Funding Agencies|National Key Research and Development program of China [2019YFA0705900]; National Natural Science Foundation of ChinaNational Natural Science Foundation of China (NSFC) [21734008, 51803178, 61721005, 21722404, 21674093]; Zhejiang Natural Science Fund for Distinguished Young Scholars [LR17E030001]; NSFC/RGC Joint Research SchemeNational Natural Science Foundation of China (NSFC) [N_CUHK418/17]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation [2016.00590]; Government Strategic Research Area in Material Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [200900971]; China Scholarship Council (CSC)China Scholarship Council

Low energy loss and efficient charge separation under small driving forces are the prerequisites for realizing high power conversion efficiency (PCE) in organic photovoltaics (OPVs). Here, a new molecular design of nonfullerene acceptors (NFAs) is proposed to address above two issues simultaneously by introducing asymmetric terminals. Two NFAs, BTP-S1 and BTP-S2, are constructed by introducing halogenated indandione (A(1)) and 3-dicyanomethylene-1-indanone (A(2)) as two different conjugated terminals on the central fused core (D), wherein they share the same backbone as well-known NFA Y6, but at different terminals. Such asymmetric NFAs with A(1)-D-A(2) structure exhibit superior photovoltaic properties when blended with polymer donor PM6. Energy loss analysis reveals that asymmetric molecule BTP-S2 with six chlorine atoms attached at the terminals enables the corresponding devices to give an outstanding electroluminescence quantum efficiency of 2.3 x 10(-2)%, one order of magnitude higher than devices based on symmetric Y6 (4.4 x 10(-3)%), thus significantly lowering the nonradiative loss and energy loss of the corresponding devices. Besides, asymmetric BTP-S1 and BTP-S2 with multiple halogen atoms at the terminals exhibit fast hole transfer to the donor PM6. As a result, OPVs based on the PM6:BTP-S2 blend realize a PCE of 16.37%, higher than that (15.79%) of PM6:Y6-based OPVs. A further optimization of the ternary blend (PM6:Y6:BTP-S2) results in a best PCE of 17.43%, which is among the highest efficiencies for single-junction OPVs. This work provides an effective approach to simultaneously lower the energy loss and promote the charge separation of OPVs by molecular design strategy. ; Funding Agencies|National Key Research and Development Program of China [2019YFA0705900]; National Natural Science Foundation of ChinaNational Natural Science Foundation of China [21734008, 21875216, 51803178, 61721005]; China Postdoctoral Science FoundationChina Postdoctoral Science Foundation [2017M621907, 2019T120501]; S&T Innovation 2025 Major Special Programme of Ningbo [2018B10055]; Research Grant Council of Hong KongHong Kong Research Grants Council [N_CUHK418/17, 14303519, 4053304]; Swedish Government Strategic Research Area in Material Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [200900971]; Swedish Research CouncilSwedish Research Council [2017-04123]; China Scholarship Council (CSC)China Scholarship Council