Dipartimento di Scienza dei Materiali, Università degli Studi di Milano Bicocca , 20125 Milano, Italy.
Nano Lett. 2014 Nov 12;14(11):6644-50. doi: 10.1021/nl503322a. Epub 2014 Oct 22.
Conventional solar cells exhibit limited efficiencies in part due to their inability to absorb the entire solar spectrum. Sub-band-gap photons are typically lost but could be captured if a material that performs up-conversion, which shifts photon energies higher, is coupled to the device. Recently, molecular chromophores that undergo triplet-triplet annihilation (TTA) have shown promise for efficient up-conversion at low irradiance, suitable for some types of solar cells. However, the molecular systems that have shown the highest up-conversion efficiency to date are ill suited to broadband light harvesting, reducing their applicability. Here we overcome this limitation by combining an organic TTA system with highly fluorescent CdSe semiconductor nanocrystals. Because of their broadband absorption and spectrally narrow, size-tunable fluorescence, the nanocrystals absorb the radiation lost by the TTA chromophores, returning this energy to the up-converter. The resulting nanocrystal-boosted system shows a doubled light-harvesting ability, which allows a green-to-blue conversion efficiency of ∼12.5% under 0.5 suns of incoherent excitation. This record efficiency at subsolar irradiance demonstrates that boosting the TTA by light-emitting nanocrystals can potentially provide a general route for up-conversion for different photovoltaic and photocatalytic applications.
传统的太阳能电池由于其无法吸收整个太阳光谱，因此效率有限。亚带隙光子通常会丢失，但如果与设备耦合的材料能够进行上转换，从而将光子能量转移到更高的能级，那么这些光子就可以被捕获。最近，经历三重态-三重态湮灭（TTA）的分子生色团在低辐照度下实现高效上转换方面显示出了前景，这适用于某些类型的太阳能电池。然而，迄今为止显示出最高上转换效率的分子系统不太适合宽带光捕获，从而降低了它们的适用性。在这里，我们通过将有机 TTA 系统与高荧光 CdSe 半导体纳米晶体结合来克服这一限制。由于它们具有宽带吸收和光谱狭窄、尺寸可调谐的荧光特性，纳米晶体吸收了 TTA 生色团损失的辐射，将能量返回上转换器。由此产生的纳米晶体增强系统显示出两倍的光捕获能力，在 0.5 个太阳的非相干激发下，绿光到蓝光的转换效率约为 12.5%。在亚太阳光辐照度下的这一记录效率表明，通过发光纳米晶体来增强 TTA 可能为不同的光伏和光催化应用提供一种通用的上转换途径。
