Light Trapping in charge transfer states for improved organic photovoltaic performance

光伏(PV)将太阳光直接转化为电能，不会产生任何温室气体。大多数商用PVs是由硅制成的，这种材料加工成本高，运输起来很重，而且很脆。这一基础研究项目有助于开发由低成本、轻重量和机械柔性的有机材料制成的光伏设备。所有光伏设备的一个问题是，阳光必须被吸收，而不是在任何入射角度下从表面反射。对于硅光伏器件，这个问题已经解决了，方法是以特定的图案粗糙硅的正面和背面，以使光被吸收到硅中，而不是反射回空间。该研究项目提出了一种类似的工艺来粗糙有机光伏层的背面，以增强特别是在太阳光谱的近红外部分的光吸收，该部分包含了很大比例的太阳能。通过这种表面粗化工艺，有机光伏器件的效率将提高，使其成为清洁能源生产的更好商业选择。这种图案还将使有机光伏在高入射角度下更有效地吸收光线，这类似于早晚的阳光。本科生和博士研究生将接受太阳能、聚合物和半导体行业有价值的研究技能培训。招生和推广活动的目的是加强少数族裔在研究科学中的代表性。迫切需要在有机光伏(OPV)设备中设计光陷阱结构，这种结构可以极大地增加电荷转移(CT)态在近红外(NIR)中的吸收。该项目的目标是使用横向光捕获结构来增强OPV设备中CT和状态的吸光度。总体目标是开发一种卷到卷(R2R)兼容的光学图案化工艺，将侧向光陷阱结构划入OPV层，从而在广泛的波长范围内提高CT&amp；状态吸收20%以上的外部量子效率(EQE)。该项目的中心假设是，OPV层的700&1000 nm 2D横向图案与厚的有源层相结合，将在CT&amp；状态下实现20%EQE的目标。这项研究的基本原理是使用溶液处理方法模仿无机薄膜光伏设备中使用的光捕获结构，使OPV具有潜在的廉价和可扩展的潜力。加州大学戴维斯分校的团队为该项目带来了OPV器件制造、光学建模和共轭聚合物合成方面的专业知识。该项目分为三个目标。目标1：使用快速光学处理创建近红外光捕获结构。工作假设是，深光陷阱结构将优化激子带隙以下的波导模，从而在近红外范围内增强吸收。目的2：合成溶解度可控的OPV材料，优化构图。高分子量和低分散性的聚合物是OPV应用的活跃供体，最大限度地提高了图案保真度。目标3：开发、测试和模拟具有创纪录功率转换效率(PCE)的图案化OPV器件。该团队将使用大面积溶液图案化技术，用最有前景的聚合物活性材料来制造图案化的OPV器件。这项基础研究将使人们能够从平坦的OPV层转向关注亚带隙状态下的光捕获。由于其他研究人员将能够采用图案化方法，行业将能够将其应用扩展到大面积有机设备应用，因此预期的意义超出了单个设备的效率。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。

Photovoltaics (PVs) convert sunlight directly into electricity without any production of greenhouse gases. Most commercial PVs are made from silicon, which is expensive to process, heavy to transport, and brittle. This fundamental research project contributes to the development of PV devices that are made from organic materials that are low-cost, light-weight, and mechanically flexible. One issue for all PV devices is that the sunlight must be absorbed and not reflected from the surface for any angle of incidence on the surface. This problem has been addressed for silicon PV devices by roughening the front and back surfaces of the silicon in a specific pattern to cause the light to be absorbed into the silicon instead of being reflected back to space. This research project addresses a similar process to roughen the back surface of the organic PV layer to enhance absorption of light specifically in the near infrared portion of the solar spectrum, which contains a large proportion of the solar energy. Through this surface roughening process, the efficiency of organic PV devices will be increased, making them a better commercial option for clean energy production. The pattern will also make the organic PV absorb light more efficiently at high incidence angles, which is similar to sunlight in the morning and evening. Undergraduate and Ph.D. graduate students will be trained with research skills that are valued in the solar, polymer, and semiconducting industries. Student recruiting and outreach activities are designed to enhance inclusion of underrepresented minorities in research science.There is a critical need to engineer light‐trapping structures into organic photovoltaic (OPV) devices that can greatly increase the charge‐transfer (CT) state absorbance in the near infrared (NIR). The goal of this project is to enhance CT‐state absorbance in OPV devices using lateral light‐trapping structures. The overall objective is to develop a roll‐to‐roll (R2R) compatible optical patterning process to scribe lateral light‐trapping structures into OPV layers that can increase the external quantum efficiency (EQE) of CT‐state absorbance above 20% across a broad wavelength range. The central hypothesis of this project is that 700‐1000 nm 2D lateral patterning of the OPV layer combined with a thick active layer will achieve this goal of 20% EQE in the CT‐states. The rationale that underlies the research is to mimic light‐trapping structures used in inorganic thin‐film PV devices using solution processing methods that make OPV potentially both inexpensive and scalable. The University of California-Davis team brings expertise in OPV device fabrication, optical modeling, and conjugated polymer synthesis to the project. The project is structured into three aims. Aim 1: Create NIR light‐trapping structures using rapid optical processing. The working hypothesis is that deep light‐trapping structures will optimize waveguide modes below the excitonic band gap, leading to enhanced absorbance in the NIR range. Aim 2: Synthesize OPV materials with controlled solubility for optimized patterning. The pattern fidelity is maximized by high molecular weight and low dispersity polymers that are active donors for OPV applications. And Aim 3: Develop, test and model patterned OPV devices with record power conversion efficiency (PCE). The team will use large‐area solution patterning to fabricate patterned OPV devices with the most promising polymeric active materials. This fundamental research will enable a departure from flat OPV layers to focus on light capture in sub‐band gap states. The expected significance extends beyond the individual device efficiency as other researchers will be able to adopt the patterning method and industry will be able to expand its use to large area organic device applications.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.