Passivation of Molecular n‐Doping: Exploring the Limits of Air Stability
Passivation of Molecular n‐Doping: Exploring the Limits of Air Stability
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DOI：
10.1002/adfm.201505092
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发表时间：
2016-06
影响因子：
19
通讯作者：
M. Tietze;Bradley D. Rose;M. Schwarze;A. Fischer;Steffen Runge;J. Blochwitz-Nimoth;B. Lüssem;K. Leo;J. Brédas
中科院分区：
文献类型：
--
作者：
M. Tietze;Bradley D. Rose;M. Schwarze;A. Fischer;Steffen Runge;J. Blochwitz-Nimoth;B. Lüssem;K. Leo;J. Brédas
分子掺杂是实现柔性、低成本有机互补半导体技术的关键技术，需要高效、稳定的p型和n型掺杂。然而，与分子p掺杂剂相比，高效n型掺杂剂通常对空气中的快速降解敏感，因为它们的电子给能所需的电离能（IEs）很低，例如，四系（1,3,4,6,7,8‐六氢‐2H‐嘧啶[1,2‐a]嘧啶）二钨（II） （W2(hpp)4）的电离能= 2.4 eV。本文通过电导率测量和光发射光谱法比较了不同基质W2(hpp)4组合的空气稳定性。发现了n掺杂对降解的部分钝化，这种效应被确定为依赖于宿主材料的特定能级。由于掺杂剂的最高占据分子轨道（HOMO）被限制在其分子中心，因此宿主- W2(hpp)4电子波函数不太可能发生杂化，这一发现可以通过将掺杂剂的单电子转移到能量水平足够低的宿主材料来实现稳定，从而避免进一步的电荷转移到氧-水复合物中。我们的研究结果表明，在空气中暂时处理n掺杂有机薄膜是可行的，例如在光刻有机场效应晶体管（ofet）的结构过程中。
Molecular doping is a key technique for flexible and low‐cost organic complementary semiconductor technologies that requires both efficient and stable p‐ and n‐type doping. However, in contrast to molecular p‐dopants, highly efficient n‐type dopants are commonly sensitive to rapid degradation in air due to their low ionization energies (IEs) required for electron donation, e.g., IE = 2.4 eV for tetrakis(1,3,4,6,7,8‐hexahydro‐2H‐pyrimido[1,2‐a]pyrimidinato)ditungsten(II) (W2(hpp)4). Here, the air stability of various host:W2(hpp)4 combinations is compared by conductivity measurements and photoemission spectroscopy. A partial passivation of the n‐doping against degradation is found, with this effect identified to depend on the specific energy levels of the host material. Since host‐W2(hpp)4 electronic wavefunction hybridization is unlikely due to confinement of the dopant highest occupied molecular orbital (HOMO) to its molecular center, this finding is explained via stabilization of the dopant by single‐electron transfer to a host material whose energy levels are sufficiently low for avoiding further charge transfer to oxygen–water complexes. Our results show the feasibility of temporarily handling n‐doped organic thin films in air, e.g., during structuring of organic field effect transistors (OFETs) by lithography.