Institute of Materials Research and Engineering, Agency for Science, Technology and Research, 3 Research Link, 117602, Republic of Singapore.
Nanoscale. 2012 Jan 21;4(2):478-85. doi: 10.1039/c1nr10858a. Epub 2011 Nov 17.
The ordered-bulk heterojunction (BHJ) photovoltaic device comprising a semiconducting donor polymer incorporated into pristine/unmodified vertically aligned arrays of metal oxide acceptor nanotubes/nanorods is widely perceived as being structurally ideal for energy conversion but the power conversion efficiencies of such devices remain relatively low (in the order of η = 0.6%) when compared with bilayer or non-ordered bulk heterojunction systems. We explain the incongruity by investigating the morphology and microstructure of regio-regular poly(3-hexyl thiophene) (P3HT) infiltrated and confined within the cavities of TiO(2) nanotube arrays. A series of TiO(2) nanotube arrays with different nanotube diameters and inter-nanotube spacings are fabricated by the liquid-phase atomic layer deposition (LALD) technique, and P3HT is infiltrated into the array cavities via a vacuum-annealing technique. X-Ray diffraction studies reveal that the P3HT chains in both nano-confined and non-confined (i.e. planar film) environments are well-aligned and oriented edge-on with respect to the underlying substrate. Up to 2.5-fold improvement in the incident-photon-to-converted-electron efficiency (IPCE) is observed in ordered-BHJ structures over benchmark planar devices which we attribute to the increase in interfacial area resulting from the use of the nanostructures. However, the large effective surface area conferred by the nano-arrays (up to 9.5 times that of the planar system) suggests that much higher efficiencies could be harnessed. Our study shows that the morphology and orientation of the infiltrated polymer play a critical role in the charge transport of the device, and suggests that better understanding and control of polymer morphology under nano-confinement in the nano-array will be the key to fully reaping the promised benefit of ordered-BHJ devices.
有序体相异质结（BHJ）光伏器件由掺入原始/未改性垂直排列的金属氧化物接受体纳米管/纳米棒的半导体给体聚合物组成，被广泛认为在结构上有利于能量转换，但与双层或无序体相异质结系统相比，此类器件的功率转换效率仍然相对较低（约为 η = 0.6%）。我们通过研究在 TiO2 纳米管阵列腔体内渗透和受限的区域规整聚（3-己基噻吩）（P3HT）的形态和微观结构来解释这种不一致性。通过液相原子层沉积（LALD）技术制备了一系列具有不同纳米管直径和纳米管间间距的 TiO2 纳米管阵列，并通过真空退火技术将 P3HT 渗透到阵列腔体内。X 射线衍射研究表明，P3HT 链在纳米受限和非受限（即平面膜）环境中都具有良好的取向性，并相对于基底呈边缘取向。与基准平面器件相比，有序 BHJ 结构中的入射光子到转换电子的效率（IPCE）提高了 2.5 倍，我们将其归因于使用纳米结构导致界面面积增加。然而，纳米阵列赋予的大有效表面积（比平面系统大 9.5 倍）表明可以利用更高的效率。我们的研究表明，渗透聚合物的形态和取向在器件的电荷输运中起着关键作用，并表明在纳米阵列中对聚合物形态的更好理解和控制将是充分利用有序 BHJ 器件所承诺的好处的关键。
