Light Trapping in charge transfer states for improved organic photovoltaic performance

光伏发电（PV）将阳光直接转化为电能，而不会产生任何温室气体。 大多数商业PV是由硅制成的，硅加工成本高，运输笨重，易碎。该基础研究项目有助于开发由低成本，重量轻，机械灵活的有机材料制成的PV器件。所有PV装置的一个问题是，对于表面上的任何入射角，太阳光必须被吸收并且不从表面反射。对于硅PV器件，已经通过以特定图案使硅的前表面和后表面粗糙化以使光被吸收到硅中而不是被反射回空间来解决这个问题。该研究项目提出了一种类似的工艺，使有机PV层的背面粗糙化，以增强对太阳光谱近红外部分的光的吸收，该部分包含很大比例的太阳能。通过这种表面粗糙化工艺，有机光伏器件的效率将得到提高，使其成为清洁能源生产的更好商业选择。该图案还将使有机光伏在高入射角下更有效地吸收光，这类似于早晨和晚上的阳光。本科和博士研究生将接受太阳能，聚合物和半导体行业的研究技能培训。招生和外展活动的目的是加强在研究science.There是一个关键的需要工程师光#8208;陷获结构到有机光伏（OPV）器件，可以大大增加电荷#8208;转移（CT）状态的吸收在近红外（NIR）。该项目的目标是使用横向光捕获结构来增强OPV器件中的CT #8208;状态吸收。总体目标是开发一种辊对辊（R2 R）兼容的光学图案化工艺，以将横向光捕获结构刻划到OPV层中，其可以在宽波长范围内将CT状态吸光度的外部量子效率（EQE）提高到20%以上。该项目的中心假设是，与厚有源层组合的OPV层的700 nm 1000 nm 2D横向图案化将在CT状态下实现20%EQE的目标。该研究的基本原理是使用溶液加工方法来模拟无机薄膜PV器件中使用的光捕获结构，该方法使OPV潜在地既便宜又可扩展。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NIR光#8208;捕获结构。工作假设是，深光#8208;捕获结构将优化激子带隙以下的波导模式，导致NIR范围内的吸收增强。目标2：合成具有受控溶解度的OPV材料以优化图案化。通过高分子量和低分散性聚合物使图案保真度最大化，所述聚合物是OPV应用的活性供体。目标3：开发、测试和建模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来制造具有最有前途的聚合物活性材料的图案化OPV器件。这项基础研究将使人们能够从平坦的OPV层出发，专注于子带隙状态下的光捕获。预期的意义超出了单个器件的效率，因为其他研究人员将能够采用图案化方法，工业界将能够将其应用扩展到大面积有机器件应用。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值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.