用氧化錫全無機電子傳導層製作高效率且穩定之反式鈣鈦礦太陽能電池研究

Efficient and Stable Inverted Perovskite Solar Cell Based on Tin Oxide Inorganic Electron Transport Layer

王彥錡(Yen-Chi Wang)

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(2021年)

https://doi.org/10.6342/NTU202100570

摘要

有機無機混成鈣鈦礦材料因具有出色的光伏特性：長載子擴散能力、高可見光吸收係數以及可藉由組成成分調控能隙等優勢，相當受到矚目，其光電轉換效率於近十年間已經達到了25.5 %。然而，作為光伏元件，鈣鈦礦太陽能電池雖已成功地提高了光電轉換效率，但元件穩定性仍然是影響其邁向實際應用並商業化的主要關鍵因素之一。於穩定性的討論中，反式結構相較於順式結構之鈣鈦礦太陽能電池具有更優異的環境穩定性，而一般反式結構的鈣鈦礦太陽能電池常會使用富勒希(C60)及其衍生物(PC61BM)作為電子傳導層，然而這些材料的成本較高，且其熱穩定性較低，在高溫操作時容易發生團聚的現象，而作為小分子的載子傳輸層，其無法有效的阻絕金屬電極於高溫下的擴散，進而降低電池元件的效率表現並且導致其穩定性不佳，因此，本研究將以穩定的n型金屬氧化物-氧化錫奈米粒子取代有機電子傳導材料。
為製備出高載子傳輸能力、尺度適當以及適用於鈣鈦礦光伏元件之氧化錫奈米粒子，本研究以化學法配合水熱法合成出具結晶性之鉭摻雜氧化錫奈米粒子(Sn0.925Ta0.075O2)，由鉭摻雜的方式，氧化錫奈米粒子相較於未摻雜的氧化錫奈米粒子具有較高的載子濃度(carrier density)，並藉此提升氧化錫薄膜的導電性，其中鉭含量從XPS分析得知為6.75 mol%。為了使分散於油相有機溶劑的Sn0.925Ta0.075O2奈米粒子表現出較佳的載子收集能力，我們以短碳鏈的3-MPA (7.5 wt%) 進行固態配基置換，減少Sn0.925Ta0.075O2奈米粒子表面的長碳鏈油酸配基，其光電轉換效率可由11.43 %提升至12.73 %。
為了進一步優化Sn0.925Ta0.075O2薄膜的電性，我們結合了高導電性的多壁奈米碳管（CNT）以增強電子的收集能力並且減少電子電洞複合的可能。將0.075 wt% CNT混摻進Sn0.925Ta0.075O2後，光電轉換效率可以達到14.61 %。最後，由於鈣鈦礦層為在空氣中利用熱鑄法所製成，其較容易產生缺陷，因此以五氟碘苯(IPFB)針對鈣鈦礦主動層和電子傳導層進行界面修飾，鈍化與鈣鈦礦界面的離子缺陷，避免載子在鈣鈦礦與電子傳導層界面間產生累積以及複合，而改質後的元件效率可更加提升至15.48 %。
在光穩定性以及高溫高濕的穩定性測試後可以得知，以p型NiOx和n型改質Sn0.925Ta0.075O2奈米粒子作為載子傳輸層之鈣鈦礦太陽能電池相較於以PC61BM作為電子傳導層的元件具有更好的穩定性。其封裝元件於連續照光(AM 1.5, Xenon lamp)和高溫高濕測試(85 oC和85 % RH)可維持80 %的初始效率超過600小時和1000小時，此結果為現今使用全無機載子傳導層之鈣鈦礦太陽能電池中穩定性最佳的結果，同時也減小了遲滯現象的發生。這些結果顯示，透過使用改質後的Sn0.925Ta0.075O2作為無機電子傳導層可以成功製備出低製造成本、良好效率表現且優異穩定性的鈣鈦礦太陽能電池。

關鍵字

鉭摻雜 ； 氧化錫 ； 富勒希衍生物 ； 固態配基置換 ； 奈米碳管 ； 鈣鈦礦 ； 太陽能電池 ； 五氟碘苯 ； 穩定性

並列摘要

Organic-inorganic hybrid perovskite materials have achieved high efficiency of 25.5 % due to their excellent characteristics of light absorption and carrier diffusion length. Although perovskite solar cells (PSCs) exhibit high-power conversion efficiency (PCE), their device stability and fabrication cost are still of great concerns which are the major issues to restrain their commercialization. For stability issue, inverted p-i-n perovskite solar cells are more environmental stable than n-i-p ones. For p-i-n perovskite solar cells, the commonly used electron transporting layers (ETLs) are fullerene (C60) and its derivatives (PC61BM), which are very expensive and suspetbile to environment. They are easy to aggregate as operating temperature increase. Moreover, these small molecules can not avoid metal electrodes diffusing at high temperature. These situations decrease the performance of the PSC devices and affect the stability of devices. Thus, we demonstrate a stable n-type metal oxide of Sn1-xTaxO2 nanoparticles to replace organic electron transport materials.
To prepare tin oxide nanoparticles with high mobility and suitable size for PSCs, we synthesized Ta-doped tin oxide nanoparticles (Sn1-xTaxO2) by chemical method and solvothermal method. Ta-doped tin oxide nanoparticles have the higher carrier density compared to the undoped ones.Ta doping can increase the carrier density to further improve the conductivity of the SnO2 film. The optimized concentration of Ta dopant is Sn0.925Ta0.075O2. Such synthesized Ta doped SnO2 nanoparticle was characterized by using X-ray photoelectron spectrum (XPS), which showed 6.75 mol% of Ta dopant. To improve electron extraction ability of Sn0.925Ta0.075O2 nanoparticles which dispersed in the oil phase organic solvents, we modified the surface of them with short carbon chain 3-MPA (7.5 wt%) by solid-state ligand exchange to reduce the long carbon chain oleic acid ligands(-OA). And the PCE increased from 11.43 % to 12.73 %.
To further improve the electric property of modified Sn0.925Ta0.075O2 film, we combine the high-conductivity multi-walled carbon nanotube (CNT) to enhance the carrier extraction and to reduce the recombination. After combining 0.075 wt% CNT to Sn0.925Ta0.075O2, the PCE reached 14.61%. Finally, to passivate the defect of perovskite film which was fabricated in air by hot-casting, iodopentafluorobenzene (IPFB) was employed to coat on the perovskite film to passivate these surface electron trapping states and reduce the carrier accumulation and recombination between the interface of perovskite and ETL. The interface modification with IPFB made PSCs exhibit a high PCE of 15.48 %.
With light soaking and damp heat test (85 oC and 85 % RH), we found that PSCs which based on p-type NiOx and n-type modified Sn0.925Ta0.075O2 nanoparticles as charge transport layers showed the better stability than the devices with PC61BM as ETL. With encapsulation, the corresponding devices maintain 80 % of the initial PCE after 600 hours during light soaking and 1000 hours of damp heat test. The results demonstrate the stability record for all-inorganic charge transport layer based perovskite solar cells with minor hysteresis. These results revealed that cost-effective, good device performance, and excellent light-soaking stability can be realized by employing modified Sn0.925Ta0.075O2 as inorganic ETL.

並列關鍵字

Tantalum-doping ； SnO2 ； solid-state ligand exchange ； carbon nanotube ； iodopentafluorobenzene ； stability ； perovskite ； solar cell ； fullerene derivatives

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