Fabrication of CZTS thin film on flexible Cu-foil substrate by two-stage process

Abstract

In this research, CZTS thin films were grown on flexible Cu-foil substrates with varying sulfurization times. Distinct characterization methods were employed, including X-ray diffraction (XRD), Raman spectroscopy, Energy-Dispersive X-ray Spectroscopy (EDX), Scanning Electron Microscopy (SEM), optical transmission, and Photoluminescence (PL) measurements. Distinctive diffraction peaks characteristic of the kesterite CZTS phase were observed in the XRD analysis, occurring around at 2θ= 28.45° (112), 47° (220/204), and 56° (312/116). Additionally, some secondary phases such as Cu2S and SnS were identified. Raman spectroscopy confirmed the presence of the kesterite CZTS phase, with a prominent peak detected at approximately ~336 cm-1, attributed to sulfur atom vibrations within the kesterite structure. Apart from CZTS structure, minor peaks suggesting the presence of the Cu2SnS3 (CTS) phase was detected. EDX analysis revealed compositions with Cu-poor content and Zn-rich content across all samples, with slight variations in sulfurization dwell times affecting the chemical composition. SEM imaging at different magnifications showed alterations in surface morphology and grain structures. Films sulfurized for 30 s and 60 s displayed a granular structure morphology, while extending the dwell time to 120 s resulted in a more compact surface morphology. Optical band gap values ranged between 1.57 and 1.60 eV. PL measurements consistently exhibited strong PL emission around 1.25 eV for all samples, attributed to various transitions within the band structure of CZTS film. The absence of observable band-to-band transitions in the PL measurements indicated the presence of intrinsic defect levels and recombination centers within CZTS. Overall, it was demonstrated in this study that CZTS thin films can be produced on flexible Cu-foils with short sulfurization times, thereby expanding the application areas of CZTS thin-film solar cells.

Keywords

• CZTS thin film
• Cu-foil
• Sputtering
• RTP
• Short sulfurization time

İki aşamalı yöntem ile CZTS ince filmlerinin esnek Cu-folyo altlık üzerine büyütülmesi

Öz

Bu araştırmada, farklı sülfürleme süreleri ile esnek Cu-folyo üzerine büyütülmüş CZTS ince filmler incelendi. X-ışını kırınımı (XRD), Raman spektroskopisi, Enerji Dağılımlı X-ışını spektroskopisi (EDX), Taramalı Elektron Mikroskopisi (SEM), optik geçirgenlik ve fotolüminesans (PL) ölçümleri de dahil olmak üzere çeşitli karakterizasyon yöntemleri kullanıldı. XRD analizinde kesterit CZTS fazına özgü belirgin kırınım pikleri 2θ= 28.45° (112), 47° (220/204) ve 56° (312/116) civarında meydana gelen pikler gözlemlendi. Ayrıca, Cu2S ve SnS gibi bazı ikincil fazlar tespit edildi. Raman spektroskopisi, kesterit CZTS fazının varlığını doğruladı ve kesterit yapısı içindeki kükürt atomu titreşimlerine atfedilen yaklaşık ~336 cm-1'de belirgin bir pik tespit edildi. CZTS yapısının yanı sıra, Cu2SnS3 (CTS) fazının varlığını işaret eden az sayıda pik de tespit edildi. EDX analizi, tüm örneklerin Cu-fakiri ve Zn-zengini kompozisyona sahip olduğunu göstermiştir. Farklı büyütme oranlarında yapılan SEM görüntülemeleri yüzey morfolojisinde ve tane yapılarında değişiklikler olduğunu gösterdi. 30 ve 60 saniye süreyle sülfürlenmiş filmler taneli bir yapı morfolojisi sergilerken, bekleme süresini 120 saniyeye uzatmak daha kompakt bir yüzey morfolojisine katkı sağladığı tespit edilmiştir. Optik bant aralığı değerleri 1.57 ile 1.60 eV arasında değişkenlik göstermiştir. PL ölçümleri, tüm örneklerde 1.25 eV civarında güçlü bir PL emisyonu sergiledi ve bu, CZTS yapısı içindeki çeşitli geçişlere atfedildi. PL ölçümlerinde gözlemlenen banttan banta geçişlerinin olmaması, CZTS içindeki özden kusur seviyeleri ve rekombinasyon merkezlerinin varlığını işaret ettiği belirlenmiştir. Genel olarak, bu çalışmada CZTS ince filmlerin kısa sülfürleme süreleriyle esnek Cu-folyolar üzerine üretilebileceği ve bu sayede CZTS ince film güneş pillerinin uygulama alanlarının genişletilebileceği gösterilmiştir.

Anahtar Kelimeler

• CZTS ince film
• Cu-folyo
• Saçtırma
• RTP
• Kısa sülfürleme süresi

Kaynakça

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