EAGER: Scalable Organic Shortwave Infrared Photodiodes

对短波红外(SWIR)光响应的光电探测器是构成科学、工业、医疗和国防应用的基础的广泛的光谱系统和光电子学的关键。SWIR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，而且广泛使用负担不起。新的替代材料备受追捧，特别是那些可以直接沉积以取代复杂制造工艺的材料。有机半导体允许直接从溶液中沉积，并实现了可伸缩性，但到目前为止仅限于可见光和近红外光谱。本项目将研究一类有前景的新型SWIR聚合物光电二极管，以揭示将有机物的用途扩展到目前由无机材料主导的SWIR光谱所需的基本性质。如果成功，拟议的研究将提供一种变革性的能力，以实现广泛部署的SWIR系统，这是传统半导体无法实现的，并可能使依赖SWIR传感的各种应用发生革命性变化。该项目为研究生和本科生提供了与行业合作伙伴进行交流访问和实习的机会。该团队将在推广活动中展示研究成果，包括为服务不足学校的高中生和教师举办的动手讲习班，以及为社区大学的学生举办的暑期研究项目。该项目的目标是找到用于探测短波红外光的有机体异质结光电二极管的光谱范围和探测能力的基本极限。本项目将研究结构-加工-性质之间的关系，并揭示从低能电荷转移(CT)态产生有效光电流的基本特征。具体地说，这项研究将测量器件的光响应和暗电流，以量化随着带隙减小而增加的光谱范围和噪声的程度。在任务1中，目标是检查CT激子解离对于高介电常数材料是否会变得有效，因为大介电常数提供了一个高度可极化的环境，这将降低电子-空穴对之间的库仑引力，从而促进解离。体相异质结的介电常数将通过掺入高k樟脑分子和在增溶侧链中使用乙二醇基的富勒烯衍生物来调节。解离效率将通过与材料S介电常数有关的瞬时光电导测量来获得。更有效的解离将使低CT态带隙产生光电流，并扩大光谱范围。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，以了解和预测光谱范围。同样的SWIR聚合物将与不同的富勒烯衍生物配对，以系统地降低CT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-复合事件可能会导致暗电流噪声的增加。电荷复合寿命将通过阻抗谱测量，以检查光谱范围和噪声之间的平衡。所获得的知识将为有机红外光电探测器的未来发展提供更好的光生成要求。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.