A Study on the Defects and Bandgap/ Electrostatic Potential Fluctuations on the Performance of Cztsse Thin-Film Solar Cells with Sub-Millimeter-Scale Grains

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Project title

Code/計畫編號

MOST104-2112-M002-023-MY3

Translated Name/計畫中文名

研究缺陷種類與能隙/靜電位能波動在次厘米晶粒之銅鋅錫硫硒薄膜太陽能電池的效能關係

Project Coordinator/計畫主持人

Cheng-Ying Chen

Funding Organization/主管機關

National Science and Technology Council

Department/Unit

Center for Condensed Matter Sciences,National Taiwan University

Website

https://www.grb.gov.tw/search/planDetail?id=11569743

Year

2015

Start date/計畫起

01-08-2015

Expected Completion/計畫迄

31-07-2016

Bugetid/研究經費

533千元

ResearchField/研究領域

物理
光電工程
能源工程

發展太陽能發電等再生能源是世界之趨勢。目前銅銦鎵硫硒Cu(In,Ga)(S,Se)2 (CIGSSe)薄膜太陽能電池最高效率可達20.3%，是各種薄膜太陽能電池中效率處於領先群的地位。但因為銦、鎵元素是含量稀少之金屬，因此開發利用鋅及錫替代稀有金屬銦及鎵之材料：銅鋅錫硫硒Cu2ZnSn(Se,S)4 (CZTSSe)。目前CZTSSe 太陽能電池最高效率僅~12%。其主要瓶頸是開路電壓(open circuit voltage, VOC) 一直無法提高(voltage deficit, Eg/q-VOC < 0.5V in CIGSSe, 而Eg/q-VOC > 0.6V in CZTSSe)，其主要的原因是能隙與靜電位能的波動(bandgap fluctuation and electrostatic potential fluctuation)。造成波動的主因(1)材料成分在空間分布不均(2) 材料點缺陷(defect)或複合缺陷(defect complex, such as [CuZn- + ZnCu+])所導致的，而缺陷與成分不均之處多發生在晶界(grain boundary)。本計畫將利用新的成長技術成長具有次厘米大晶粒(sub-millimeter-scale grains)之CZTSSe 較高品質的薄膜，並利用非接觸式量測:光激螢光放光技術(photoluminescence spectroscopy, such as external luminescence efficiency, full width at half maximum, micro-PL mapping, activation energy, carrier lifetime) ，以及接觸式量測: 阻抗分析儀(admittance spectroscopy, such as activation energy)研究電池效能參數與缺陷種類或晶粒大小之間的物理關係。The development of solar power as renewable energy is a global trend. Recently, the efficiency of Cu(In,Ga)(S,Se)2 (CIGSSe) solar cells can reach up to 20.3%, which is in the lead of thin film solar cells. However, In and Ga are rare-earth materials; so there is a clear quest for developing alternative compounds, such as Cu2ZnSn(Se,S)4 (CZTSSe). The CZTSSe absorbers adopt a kesterite-based crystal structure analogous to the CIGSSe chalcopyrite structure, with In and Ga from CIGSSe replaced by more abundant and lower cost Zn and Sn. Recently, the best efficiency, among all reported values, of CZTSSe solar cells is at ~12%, still far from expectation. The main bottleneck of CZTSSe is its lower open circuit voltage (voltage deficit, Eg/q-VOC < 0.5V in CIGSSe, whereas typical Eg/q-VOC > 0.6V in CZTSSe), resulting from bandgap fluctuation and electrostatic potential fluctuation. These fluctuations are originated from (1) spatial variation in composition and (2) material defects or defect complexes (such as [CuZn- + ZnCu+]), which are commonly observed near the grain boundires. In this proposal, we will develop a novel growth method to grow highquality CZTSSe thin film with sub-millimeter-scale grains. Systematic investigations on the correlation between the performance of the CZTSSe solar cells and possible origins of defects as well as their grain size will be conducted by using both contactless and contact measurements. For the first type, photoluminescence spectroscopies will be employed for studying a range of physical properties, such as external luminescence efficiency, full width at half maximum, micro-PL mapping, activation energy, and carrier lifetime. Whereas the main tool for contact measurement will be admittance spectroscopy for defect analyses such as activation energy.

Keyword(s)

銅鋅錫硫硒
薄膜太陽能電池
材料缺陷與晶界
光激螢光分析
阻抗分析
CZTSSe
thin film solar cells
defect and grain boundary
photoluminescence spectroscopies
admittance spectroscopy

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A Study on the Defects and Bandgap/ Electrostatic Potential Fluctuations on the Performance of Cztsse Thin-Film Solar Cells with Sub-Millimeter-Scale Grains

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