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某些共轭聚合物具有发光性能，有望作为发光二极管之类应用，其性能主要受最大可能的理论电致发光效率的限制 [1， 2]。若最低能量激发态强束缚激子处于单线态或三线态下的电子－空穴对），则电致发光的理论上限仅为相应光致发光量子效率的 25％：即一个处于π－带内的电子和一个处于π－带的空穴（或缺少电子态）可形成一种自旋多重性为 3的三线态，或一种自旋多重性为 1的单线态。只有单线态才能辐射跃迁而发光 [3]。如果电子－空穴对的束缚能足够 弱的话，电致发光和光致发光的最大量子效率之比理论上可接近于 1。在本文，我们将报导，若在 共轭聚合物内混入电子传输材料，则可改善电子注入特性，所得到的聚合物发光二极管的电致发光效率和光致发光效率之比可接近 50％。若假定它们处于最低激发态，这个值显然高于强束缚单线态和三线态激子的理论极限值。我们的的这个结果意味着，这种激子的束缚能很弱，或者是形成单线态的几率可能要比形成三线态的几率高得多。
Some conjugated polymers have luminescent properties and are expected to be used as light-emitting diodes. Their performance is mainly limited by the theoretical maximum possible electroluminescent efficiency [1,2]. If the lowest energy excited state strong bound exciton in singlet or triplet state under the electron-hole pairs), the theoretical upper limit of electroluminescence is only 25% of the corresponding photoluminescence quantum efficiency: a π- band An electron in the π-band and a hole in the π-band (or in the absence of the electron) form a triplet with spin-multiplicity 3 or a singlet with spin-multiplicity 1. Only singlet states can radiate transitions and emit light [3]. If the electron-hole pair binding energies are weak enough, the ratio of the maximum quantum efficiency of electroluminescence to photoluminescence can theoretically be close to unity. Here, we report that the incorporation of an electron-transporting material into a conjugated polymer can improve the electron injection characteristics, and the resulting polymer light-emitting diode can have a ratio of the electroluminescent efficiency to the photoluminescent efficiency of approximately 50%. This value is obviously higher than the theoretical limit of the strongly bound singlet and triplet excitons, assuming they are in the lowest excited state. Our result of this implies that the exciton can be very weakly bound or that the probability of forming a singlet may be much higher than the probability of forming a triplet.