EAGER: Scalable Organic Shortwave Infrared Photodiodes

响应短波红外（SWIR）光的光电探测器对于各种光谱系统和光电子学至关重要，这些系统和光电子学构成了科学、工业、医疗和国防应用的基础。短波红外技术仍然在很大程度上依赖于无机晶体，这需要复杂的制造工艺，成本高昂，无法广泛使用。新的替代材料备受追捧，尤其是那些允许直接沉积以取代复杂制造工艺的材料。有机半导体允许从溶液中直接沉积并实现可扩展性，但迄今为止仅限于可见光和近红外光谱。该项目将研究一类有前途的新型短波红外聚合物光电二极管，以揭示将有机物的实用性扩展到目前由无机材料主导的短波红外光谱所需的基本特性。如果成功，拟议的研究将提供一种变革性的能力，以实现可广泛部署的SWIR系统，这是传统半导体无法实现的，并可能彻底改变依赖SWIR传感的各种应用。该项目为研究生和本科生提供与工业合作伙伴进行交流访问和实习的机会。该研究小组将通过为高中学生和教师举办的实践研讨会以及为社区大学学生举办的暑期研究项目等外展活动展示研究成果。该项目的目标是找到有机体异质结光电二极管用于检测短波红外光的光谱范围和检测率的基本限制。该项目将研究结构-加工-性质关系，并揭示从低能电荷转移（CT）态有效产生光电流的基本特征。具体而言，本研究将测量器件的光响应和暗电流，以量化光谱范围和噪声随带隙减小而增加的程度。在任务1中，目标是检查CT激子解离是否将在高介电常数材料下变得有效，因为大介电常数呈现高度可极化的环境，这将降低电子-空穴对之间的库仑吸引力，从而促进解离。将通过在高介电常数分子中混合和通过在增溶侧链中使用具有乙二醇单元的富勒烯衍生物来调节本体异质结的介电常数。的解离效率将获得从瞬态光电导测量有关的材料？s介电常数。更有效的解离将使光电流产生从低CT状态带隙和扩展光谱范围。在任务2中，目标是确定在复合占主导地位之前仍然允许激子解离的最小CT态能量，以理解和预测光谱范围。相同的SWIR聚合物将与各种富勒烯衍生物配对，以系统地降低CT状态带隙，从而增加光谱范围。随着CT态带隙的显著减小，更多的热产生-复合事件将可能导致暗电流噪声的增加。将通过阻抗谱测量电荷复合寿命，以检查光谱范围和噪声之间的平衡。由此产生的知识将提供更好的理解的光生要求的有机红外photodetectors.This奖项的未来发展反映了NSF的法定使命，并已被认为是值得的支持，通过评估使用基金会的智力价值和更广泛的影响审查标准。

Photodetectors responsive to shortwave infrared (SWIR) light are critical to a wide range of spectroscopic systems and optoelectronics that form the foundation for scientific, industrial, medical, and defense applications. SWIR technologies remain largely dependent on inorganic crystals, which require complex manufacturing processes that are cost-prohibitive and not affordable for widespread use. New alternative materials are highly sought after, especially the ones that allow direct deposition to replace complex manufacturing processes. Organic semiconductors allow direct deposition from solutions and enable scalability but so far are limited to the visible and near-infrared spectrum. This project will investigate a promising class of novel SWIR polymeric photodiodes to reveal the fundamental properties necessary for extending the utility of organics into the SWIR spectrum currently dominated by inorganic materials. If successful, the proposed research will offer a transformative capability to realize widely deployable SWIR systems that are not achievable with conventional semiconductors and will potentially revolutionize a wide variety of applications that rely on SWIR sensing. This project provides graduate and undergraduate students opportunities for exchange visits and internships with an industrial partner. The team will showcase research results in outreach activities, which include hands-on workshops for high-school students and teachers from under-served schools and summer research programs for students from community colleges.The project goal is to find the fundamental limits on the spectral range and detectivity of organic bulk heterojunction photodiodes for detecting shortwave infrared light. This project will study structure-processing-property relationships and unveil the essential characteristics for effective photocurrent generation from low-energy charge-transfer (CT) states. Specifically, this study will measure the device photoresponse and dark current to quantify the extent of spectral range and noise increase with bandgap reduction. In Task 1, the objective is to examine if CT exciton dissociation will become efficient with high permittivity materials, because large permittivity presents a highly polarizable environment that will reduce the Coulombic attraction between the electron-hole pair and thus facilitate dissociation. The permittivity of the bulk heterojunction will be adjusted by blending in high-k camphoric molecules and by using fullerene derivatives with ethylene glycol units in solubilizing side-chains. The dissociation efficiency will be obtained from transient photoconductivity measurements in relation to a material?s permittivity. More effective dissociation will enable photocurrent generation from low CT-state bandgaps and extend spectral range. In Task 2, the objective is to determine the minimum CT-state energy that still allows exciton dissociation before recombination dominates, to understand and predict spectral range. The same SWIR polymer will be paired with various fullerene derivatives to systematically lower CT-state bandgaps and thus increase spectral range. As the CT-state bandgap is significantly reduced, more thermal generation-recombination events will likely lead to an increase in dark current noise. The charge recombination lifetime will be measured via impedance spectroscopy to examine the balance between spectral range and noise. The resulting knowledge will provide better understandings of the photogeneration requirements for future development of organic infrared photodetectors.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.