以量化的型態學分析來研討高分子薄膜太陽能電池效率的增進

Quantitative Morphology Analysis Study for Improving Polymer Solar Cell Efficiency

林聰翰(Tsung-Han Lin)

指導教授 ： 林唯芳

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.01377

摘要

此論文分兩種方式來增進高分子太陽能電池的效率，並以量化的型態學分析來研討其效率增進的機制。
本研究分為兩部分，第一部分中，我們發現利用兩階段退火處理能有效提升此類太陽能電池效率(P3HT/PCBM)達31% (自一階段退火的2.91%提升到3.80%)，為了瞭解元件內部結構發生的變化，我們利用掠角X光繞射分析去量化計算薄膜表面中P3HT以及PCBM在不同溫度退火以及經過不同退火階段所發生的改變，首先我們利用廣角X光繞射觀察P3HT (100)結晶面在經過不同退火處理下的變化，我們發現P3HT在經過退火後Z方向結晶大小明顯提升，X方向結晶大小有下降的趨勢，不過在不同的退火情況下(90, 110, 150℃)，P3HT結晶度皆無明顯改變，因此我們推論在不同退火處理下造成效率的變化主要來自PCBM聚集度的改變。
為了得到PCBM在不同退火處理下的結構演變，我們利用小角度X光散射分析PCBM在不同退火處理下聚集以及與P3HT的關係，並且也做變溫小角度X光散射分析以觀察在退火過程中，PCBM結構的變化。 在量化分析小角度X光散射的數據上，我們結合了兩種分析模型Debye-Anderson-Brumberger (DAB) model 以及 Polydispersed Hard-Sphere model有效的算出PCBM聚集顆粒體積比例，顆粒大小等參數，並由Porod law算出PCBM間比表面積的大小，結合這些數據以及元件效率，我們可以有效建立出P3HT/PCBM經過退火處理後的結構演變，並提供一個新穎的方法有效的分析有機薄膜太陽能電池內部結構。
在第二部分，我們利用適量無機奈米粒子硫化銅(0.28 wt%)的引入，並搭配適當的退火處理將元件效率自同樣處理情況的3.5%提升至4.3%，提升約23%，在上一部分建立的小角度X光散射分析模型基礎下，我們利用兩種不同的Polydispersed Hard-Sphere model同樣對此類元件做一系列不同濃度硫化銅以及不同退火處理條件下的量化分析，我們發現加入硫化銅奈米粒子後，PCBM有類似退火後聚集的現象，經由此分析模型，我們提出一種新的方法分析加入奈米粒子添加劑對元件內部結構的改變，也提供了一個新的方法提升有機太陽能電池元件效率。
本篇論文中，學生利用兩種不同的方式來優化有機高分子太陽能電池的效率，分別為二階段的退火處理以及引入無機奈米粒子添加劑，皆能使P3HT/PCBM系統所製成的有機太陽能電池效率達到4%左右，而主要效率的提升來自於P3HT/PCBM薄膜型態上發生顯著的改變。 此研究發現，當退火溫度低於PCBM的Tc時(~130℃)，所形成的PCBM聚集體較為鬆散；當退火溫度高於PCBM的Tm時(~149℃)，所形成的PCBM聚集體較為緊密，因此當我們利用150℃對元件做兩階段退火時，所形成的PCBM聚集體平均半徑最大，數量最多，同時也排列得較緊密形成較為連貫的電子傳導路徑，所做出的元件效率也達到此系列最高值3.8%；另外，我們可以藉由引入適量的小顆粒無機奈米粒子(4~5 nm)的方式達到類似退火的效果，使PCBM聚集體平均半徑變大，數目變多，但是一旦我們添加過量的奈米粒子添加劑進入元件，會使得奈米粒子本身形成聚集，晶種數目變少，差異性變大，導致PCBM聚集體數目降低，元件效率也因此略降，而在此系列研究能達到效率最高到4.3%。

關鍵字

有機高分子太陽能電池 ； 掠角小角度X光散射 ； 退火 ； 無機奈米粒子 ； 量化分析

並列摘要

In this thesis, there are two different methods we used to optimize the performance of polymer solar cell, and we study the enhancement of efficiency by improved quantitative analysis. The organic photovoltaic devices we studied are based on the system of poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methyl ester (P3HT: PC61BM).
In the first part, we utilized the method of two-stage annealing to enhance the power conversion efficiency (PCE) (31% compared to one-stage annealing; from 2.91% to 3.80%) of the organic photovoltaic devices and constructed a scheme of the evolution of morphology after two-stage annealing by the measurement of grazing-incidence wide-angle X-ray diffraction (GIWAXD) and grazing-incidence small-angle X-ray scattering (GISAXS). From GIWAXD, we can get the information of the crystallinity of P3HT (100) planes and we figured out that the intensity increased apparently once the devices were annealed. But there were almost no change between the different thermal conditions (90, 110, 150℃). As a result, we needed in-depth information of PCBM so that we did the GISAXS measurement to know the difference of aggregation of PCBM after two-stage annealing. In order to understand the change of PCBM in the procedure of annealing, we also did the in-situ GISAXS measurement. To explain these data from GISAXS measurement, we combined the Debye-Anderson-Brumberger (DAB) model and Polydispersed hard-sphere model to fit the GISAXS data of our devices under different thermal conditions, include one-step annealing and two-step annealing. Besides, we can get the specific surface area of the PCBM clusters in these devices by Porod law and integrate with the model we use. From the model we established, we can figure out the evolution of the structure of P3HT and PCBM two phase system and hence provide an efficient way to improve the PCE of organic photovoltaic devices by controlling the nanostructure inside.
In the second part, we incorporated copper sulfide (Cu2S) into the P3HT/PCBM two phase system in order to enhance the performance of devices. We found out that if we added adequate amount of Cu2S (0.28 wt%) to the system, the power conversion efficiency increases ~23% compared to the devices with the same thermal condition in the first part (from 3.5% to 4.3%). To precisely know the nanostructure of nanoparticles and PCBM, we use two different Polydispersed Hard-Sphere models to fit the GISAXS data of the active layer P3HT/PCBM/Cu2S. By this combined model, we can figure out the effect of adding nanoparticles in the organic solar cell, and provide a new way to make high efficiency organic solar cell.
In conclusion, we use two-stage annealing method and additive incorporation methods to enhance the performance of devices up to about 4%. The improvement mainly comes from the change of morphology by the measurement of GISAXS. By this analysis, the loose-packing PCBM clusters formed when the annealing temperature below the Tc of PCBM (~130℃), while the dense-packing PCBM clusters formed when the annealing temperature above the Tm of PCBM (~149℃). As a result, if we use the temperature of 150 ℃ to do the two-stage annealing process, the values of mean radius and volume fraction of PCBM clusters we attained from model fitting are the largest among samples we studied. Hence the sample PR_150+PO get the best power conversion efficiency (3.8%) in the first part. Besides, we also incorporate adequate amounts of nanoparticles in the system, and we find out that the effect of adding nanoparticles is like the annealing effect. But once we add too much nanoparticles in the system, the self-aggregation caused by nanoparticles may lead the efficiency to decrease. The best power conversion efficiency we get is 4.3% if we add 0.28 wt% nanoparticles in the system.

並列關鍵字

Polymer solar cell ； grazing-incidence X-ray scattering ； annealing ； inorganic nanoparticles ； quantitative analysis

參考文獻

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