趙逸群,吳楨芬,楊曉杰,鄧大政,劉雪娥,周惠群
〈綜述與評論〉
PbS膠體量子點(diǎn)穩(wěn)定性研究進(jìn)展
趙逸群1,吳楨芬2,楊曉杰1,鄧大政3,劉雪娥1,周惠群1
(1. 昆明冶金高等??茖W(xué)校 建筑工程學(xué)院,云南 昆明 650033;2. 昆明理工大學(xué) 現(xiàn)代農(nóng)業(yè)工程學(xué)院,云南 昆明 650023;3. 昆明物理研究所,云南 昆明 650223)
PbS膠體量子點(diǎn)由于其制備簡單、成本低廉,在近紅外波段通過調(diào)節(jié)尺寸就能改變帶隙,在太陽能電池、紅外探測、LED、生物成像等多個(gè)領(lǐng)域均有廣泛的應(yīng)用,但穩(wěn)定性限制了其大規(guī)模推廣。本文總結(jié)了影響PbS膠體量子點(diǎn)穩(wěn)定性的機(jī)理,從制備、結(jié)構(gòu)、保存、使用等多個(gè)環(huán)節(jié)探討提高其穩(wěn)定性的具體措施。提出進(jìn)一步改進(jìn)PbS膠體量子點(diǎn)穩(wěn)定性的具體方法和原理,對其應(yīng)用和發(fā)展具有一定的參考價(jià)值。
PbS膠體量子點(diǎn);量子點(diǎn)的應(yīng)用;穩(wěn)定性;核殼結(jié)構(gòu)
膠體量子點(diǎn)一個(gè)顯著優(yōu)勢是可以通過改變尺寸,調(diào)整其帶隙,達(dá)到調(diào)諧響應(yīng)波段的目的[1]。PbS膠體量子點(diǎn)的玻爾半徑大(~20 nm[2-3]),可調(diào)諧范圍寬,且制備簡單,成本低廉,在太陽能電池[4-7]、紅外探測[8-13]、LED[14-18](Light-emitting Diodes,簡稱LED)、生物成像[19-20]等多個(gè)領(lǐng)域引起人們的廣泛興趣。例如:Chuang等[5]2014年報(bào)道的PbS太陽能電池,其轉(zhuǎn)換效率為8.55%;Yang等[4]2020年使用HI處理的PbS制備太陽能電池,其效率達(dá)到10.78%,如圖1(a)所示。De Iacovo等[9]2016年制備的PbS紅外探測器的比探測率高達(dá)1011cm×Hz1/2W?1;圖1(b)顯示的紅外探測器為Georgitzikis等[11]2020年制備的多像素PbS紅外探測器,該探測器在940 nm波段的比探測率達(dá)到1012cm×Hz1/2W?1。圖1(c)顯示了Sun等[14]2012年制備的PbS紅外LED的基本結(jié)構(gòu),其外量子效率達(dá)到2%;圖1(d)顯示了Santanu等[17]2019年報(bào)道的紅外LED的基本結(jié)構(gòu),其外量子效率提升到了7.9%。此外,由于PbS膠體量子點(diǎn)的響應(yīng)波段處于醫(yī)學(xué)成像窗口,醫(yī)學(xué)研究者也常用PbS膠體量子點(diǎn)成像輔助病理判斷,圖1(e)~(g)分別為Benayas等[20]于2015年對小白鼠進(jìn)行可見光成像和借助PbS膠體量子點(diǎn)紅外成像,并將前兩者融合成像的對比圖,融合后的圖像能夠較為清楚地定位到小鼠體內(nèi)的病變部位。由此可見PbS膠體量子點(diǎn)由于其獨(dú)特的性能在多個(gè)領(lǐng)域引起了人們的持續(xù)深入研究。
圖1 PbS膠體量子點(diǎn)的應(yīng)用:(a) 太陽能電池領(lǐng)域[4];(b) 紅外探測器領(lǐng)域[11];(c) 含PbS膠體量子點(diǎn)的LED結(jié)構(gòu)[14];(d) 另一種基于PbS膠體量子點(diǎn)的LED結(jié)構(gòu)[17];注射了量子點(diǎn)的小白鼠的(e)可見光成像;(f)紅外成像和(g)融合成像[20]
目前,PbS膠體量子點(diǎn)通常采用如圖2(a)所示的熱注入法[21-23]進(jìn)行制備。Moreels等[24]合成了3.7~6.8nm尺寸的PbS膠體量子點(diǎn),相應(yīng)帶隙范圍在1.28~0.71eV,對應(yīng)吸收峰在970~1740nm。Zhang等[25]在合成PbS膠體量子點(diǎn)時(shí),通過改變?nèi)芤旱臏囟?,發(fā)現(xiàn)量子點(diǎn)的尺寸分別為3.2nm、3.3nm、3.6nm和4.1nm時(shí),對應(yīng)的吸收峰分別為973nm、1011nm、1070nm和1181nm。研究表明,PbS膠體量子點(diǎn)的尺寸和其帶隙呈現(xiàn)如下關(guān)系[26-27]:
式中:g()是PbS膠體量子點(diǎn)的禁帶寬度;為該量子點(diǎn)的直徑。根據(jù)公式(1),當(dāng)PbS膠體量子點(diǎn)的尺寸在2.07~10nm范圍內(nèi)調(diào)節(jié)時(shí),相應(yīng)帶隙范圍在1.85~0.59eV,對應(yīng)特征吸收峰在0.67~2.10mm波段,可以覆蓋整個(gè)短波紅外窗口。此外,PbS膠體量子點(diǎn)在實(shí)現(xiàn)多激子效應(yīng)[28]方面顯示出巨大的潛力。因此,PbS膠體量子點(diǎn)在多個(gè)涉及短波紅外波段的領(lǐng)域均有廣泛的應(yīng)用前景。
PbS膠體量子點(diǎn)用于光電器件時(shí),其環(huán)境穩(wěn)定性非常重要。由于量子點(diǎn)具有很高的比表面積[29],非常容易受到環(huán)境影響,導(dǎo)致其性質(zhì)發(fā)生不可預(yù)知的變化。對于富鉛表面[24, 30-31],即使大約1ppm的O2分子[32],也能在量子點(diǎn)表面形成氧化分子。所以,穩(wěn)定性限制了PbS膠體量子點(diǎn)的大規(guī)模應(yīng)用。
PbS膠體量子點(diǎn)失效的根本原因在于保存和使用時(shí),晶粒表面的S2-被氧化形成SO32-,進(jìn)一步氧化形成SO42-;Pb2+與O2-結(jié)合形成PbO,或者與SO32-、SO42-結(jié)合形成PbSO3[33]、PbSO4[30, 33],并逐步向晶粒內(nèi)部發(fā)展[34]。Zhang等[35]通過表面電位光譜測量等手段進(jìn)一步揭示在PbS膠體量子點(diǎn)中氧分子誘導(dǎo)間隙態(tài)(如圖2(d)所示)的機(jī)理。PbS膠體量子點(diǎn)表面氧化是量子點(diǎn)失效的主要推動(dòng)力[36],而H2O中通常會(huì)有一定的O2和羥基(-OH),所以在制備、保存和使用PbS膠體量子點(diǎn)的環(huán)節(jié)應(yīng)盡量避免O2和H2O的混入。
圖2 PbS膠體量子點(diǎn):(a) 熱注入法生產(chǎn)PbS膠體量子點(diǎn);(b) PbS/CdS核殼結(jié)構(gòu);(c) PbS/CdS/ZnS核殼結(jié)構(gòu); (d) PbS膠體量子點(diǎn)中氧誘導(dǎo)的間隙態(tài)[35]
在不同的環(huán)境中,PbS失效的時(shí)間不同,通常有3方面的因素:①量子點(diǎn)大小及表面性質(zhì)對穩(wěn)定性的影響。隨著合成PbS膠體量子點(diǎn)化學(xué)計(jì)量比的變化及合成尺寸的不同,其晶粒表面的原子種類及表面所屬晶面有所區(qū)別[30-31],不同原子的各種晶面其環(huán)境穩(wěn)定性不同。②環(huán)境中O2和H2O含量高低對穩(wěn)定性的影響。當(dāng)PbS膠體量子點(diǎn)所處的環(huán)境含有較多O2和H2O時(shí),PbS的穩(wěn)定性會(huì)下降。③PbS結(jié)構(gòu)的影響。熱注入法制備的PbS膠體量子點(diǎn),其表面通常覆蓋一層有機(jī)物,這層有機(jī)物常被稱為配體[29]。由于所用前驅(qū)體的不同,其配體也有所差異,配體的存在阻止了PbS膠體量子點(diǎn)的團(tuán)聚和急劇氧化,表面配體的覆蓋率越高,PbS膠體量子點(diǎn)的表面越難被氧化[30];較長的配體以及殼結(jié)構(gòu)都會(huì)增強(qiáng)其穩(wěn)定性。此外,量子點(diǎn)表面鈍化[4, 10, 37-39]和增強(qiáng)電子供體[33]的措施也有一定效果。
根據(jù)影響PbS膠體量子點(diǎn)穩(wěn)定性的3個(gè)因素,可從以下方面進(jìn)行改善:①改善PbS膠體量子點(diǎn)的制備、保存和使用環(huán)境,減少O2和H2O的混入;②對于波段不敏感的應(yīng)用領(lǐng)域,控制Pb和S原子的化學(xué)計(jì)量比,同時(shí)控制量子點(diǎn)的尺寸,使其外表面為由Pb原子組成的(111)晶面[30-31],以增強(qiáng)PbS膠體量子點(diǎn)的穩(wěn)定性;③采用核殼結(jié)構(gòu),在PbS膠體量子點(diǎn)表面再包裹一層性能更穩(wěn)定的物質(zhì),增強(qiáng)核的穩(wěn)定性。例如:通過陽離子置換,在PbS外面包裹一層CdS,形成核殼結(jié)構(gòu)[38, 40-41],如圖2(b)所示。④從PbS膠體量子點(diǎn)生產(chǎn)到使用環(huán)節(jié),盡量減少其不穩(wěn)定階段的時(shí)間。例如,配體置換[6]可以在從母液中分離PbS時(shí)進(jìn)行,也可以在制備器件時(shí)進(jìn)行;從穩(wěn)定性的角度出發(fā),長鏈比短鏈更有利于量子點(diǎn)保存,在制備器件時(shí)再進(jìn)行配體置換利于PbS膠體量子點(diǎn)的穩(wěn)定。
表1列出了幾種常用技巧的適用領(lǐng)域及優(yōu)缺點(diǎn)。改善制備環(huán)境,幾乎是所有采用熱注入法制備PbS膠體量子點(diǎn)要考慮的首要因素。所以,使用熱注入法生產(chǎn)PbS時(shí),首先,需要在三口燒瓶中進(jìn)行充分換氣[38],使三口燒瓶中的氣體及物料幾乎不含O2才進(jìn)行下一步的合成操作。換氣的充分程度是成功制備PbS膠體量子點(diǎn)的基礎(chǔ)。但是,有些學(xué)者[1, 40]使用PbO作為Pb的前驅(qū)體,有些學(xué)者[42-43]使用無機(jī)Pb鹽作前驅(qū)體,還有的學(xué)者[43-44]使用有機(jī)鉛鹽作前驅(qū)體。不同Pb前驅(qū)體的含氧量有所區(qū)別,所制備的量子點(diǎn)穩(wěn)定性不同,但尚未發(fā)現(xiàn)這幾種Pb前驅(qū)體所制備的量子點(diǎn)穩(wěn)定性的對比研究,其可能原因是采用不同Pb前驅(qū)體時(shí),S前驅(qū)體也有所不同。有部分學(xué)者[45-47]研究三辛基膦(Trioctylphosphine,簡稱TOP)在量子點(diǎn)制備過程中的機(jī)理,發(fā)現(xiàn)TOP的引入可以提升量子產(chǎn)率和穩(wěn)定性,并研究了TOP還原性的作用??紤]到PbS制備過程中,可能會(huì)在原料和氣氛等多個(gè)環(huán)節(jié)殘存O2,還原性物質(zhì)和O2結(jié)合減少了制備環(huán)境中殘存O2的含量應(yīng)是一個(gè)重要原因;但很少有學(xué)者對其它還原性物質(zhì)進(jìn)行研究,也沒有看到這些物質(zhì)還原性高低的定量指標(biāo)。相同條件下,使用PbS膠體量子點(diǎn)制備器件時(shí),在手套箱中進(jìn)行比在空氣中進(jìn)行的穩(wěn)定性更好。
表1 增強(qiáng)PbS膠體量子點(diǎn)穩(wěn)定性的技巧
Choi研究組[31]和Beygi研究組[30]發(fā)現(xiàn),不同粒度的PbS膠體量子點(diǎn)與不同計(jì)量比相匹配,可使量子點(diǎn)表面的晶面有所不同(如圖3(a)所示)。Pb過量,粒徑小于2.7nm時(shí),晶粒為圖3(b)所示的八面體;粒徑大于4.74nm時(shí),晶粒為圖3(c)所示的立方八面體,中等粒徑時(shí)為沒有頂點(diǎn)的八面體(八面體向立方八面體的過度結(jié)構(gòu))[30]。小晶粒為八面體時(shí),晶粒表面為(111)晶面,表面自由能最低[30],其表面原子展開如圖3(d)所示,整個(gè)表面全部由Pb原子組成;大晶粒為(100)晶面和(111)晶面組合的立方八面體時(shí),表面自由能最低[30],其表面原子展開如圖3(e)所示,晶粒表面除了由Pb原子組成的(111)晶面外,還有由Pb原子和S原子交錯(cuò)形成的(100)晶面;中等尺寸時(shí),為達(dá)到表面自由能最低,(100)晶面和(111)晶面均有出現(xiàn),(100)晶面的比例相對較少。Beygi等[49]的XPS研究也表明,PbS膠體量子點(diǎn)氧化伴隨著PbSO3和PbSO4化合物在量子點(diǎn)的(100)面上形成。一般認(rèn)為,由Pb組成的(111)晶面穩(wěn)定性更強(qiáng),當(dāng)PbS粒度小于2.7nm且其表面均為Pb原子時(shí),其環(huán)境穩(wěn)定性顯著增強(qiáng)[30]。
Pichaandi等[50]總結(jié)PbS、PbSe和CdS的穩(wěn)定性,發(fā)現(xiàn)穩(wěn)定性依次減弱的順序是:CdS>PbS>PbSe,于是采用相對穩(wěn)定的化合物作殼,保護(hù)穩(wěn)定性更弱的處于核心的量子點(diǎn)。為了增強(qiáng)PbSe的穩(wěn)定性,在制備好PbSe后,向含有過量Pb前驅(qū)體的母液中注入S源,在PbSe表面形成PbS殼,通過PbS殼層增加PbSe的穩(wěn)定性[50];同理,為了改善PbS膠體量子點(diǎn)的穩(wěn)定性,可以在PbS母液中,通過陽離子交換,使PbS表面置換為CdS,形成如圖2(b)所示的PbS/CdS結(jié)構(gòu)[38-41],增強(qiáng)PbS的穩(wěn)定性。綜合看來,使用核殼結(jié)構(gòu)增強(qiáng)穩(wěn)定性,是利用更活潑的金屬進(jìn)行陽離子交換,或者利用活動(dòng)性更強(qiáng)的非金屬代替陰離子。這兩種置換方式均可形成離子鍵成分更多的殼結(jié)構(gòu),從而保護(hù)內(nèi)部離子鍵成分較少的量子點(diǎn),以增強(qiáng)穩(wěn)定性。同理,相對于PbS而言,ZnS的離子鍵成分更多,且生物毒性低,在醫(yī)學(xué)成像領(lǐng)域,多使用ZnS殼包裹PbS核或者PbS/CdS核殼結(jié)構(gòu),形成PbS/ZnS二層核殼結(jié)構(gòu)[51]或如圖2(c)所示的PbS/CdS/ZnS三層核殼結(jié)構(gòu)[20]。在這種結(jié)構(gòu)中,ZnS殼不僅增強(qiáng)了PbS膠體量子點(diǎn)的穩(wěn)定性,還增強(qiáng)了PbS在水溶液中的分散能力,降低了PbS膠體量子點(diǎn)的生物毒性。此外,除常用CdS和ZnS作為PbS殼外,也有研究者使用MnS[16]作為PbS膠體量子點(diǎn)的殼。
使用熱注入法制備PbS膠體量子點(diǎn),其表面配體一般是長鏈有機(jī)物;若直接制備成光電器件,長鏈配體會(huì)使量子點(diǎn)間距離偏大,從而影響器件的電荷收集效率和傳輸效率[36, 52-53],同時(shí)量子點(diǎn)表面的高密度陷阱態(tài)[39]對器件性能不利。為了縮短PbS膠體量子點(diǎn)的層內(nèi)間距及層間距,在制備光電器件時(shí),通常對PbS膠體量子點(diǎn)進(jìn)行配體置換,將絕緣的有機(jī)配體(如:油酸配體)替換為無機(jī)配體,尤其是鹵素配體[10],無機(jī)配體對量子點(diǎn)的表面處理顯著增強(qiáng)了量子在空氣環(huán)境中的抗氧化能力[49]。短且導(dǎo)電性強(qiáng)的無機(jī)配體取代原來的長鏈有機(jī)配體后可以削弱量子點(diǎn)表面的陷阱態(tài)[39],但同時(shí),置換后PbS膠體量子點(diǎn)的團(tuán)聚性增強(qiáng)[36, 53]。所以,從防止團(tuán)聚的角度出發(fā),應(yīng)在制備光電器件的過程中進(jìn)行配體置換而不是在分離PbS時(shí)就直接進(jìn)行配體置換,這樣可以減少帶短鏈配體PbS量子點(diǎn)的保存時(shí)間;若有暴露在有氧環(huán)境可能時(shí),則盡可能在暴露之前進(jìn)行無機(jī)配體的置換。
圖3 PbS膠體量子點(diǎn)的尺寸與形狀:(a) PbS膠體量子點(diǎn)尺寸與形狀的關(guān)系[30];(b) 八面體結(jié)構(gòu)的PbS膠體量子點(diǎn);(c) 八面體表面原子展開圖;(c) 立方八面體結(jié)構(gòu)的PbS膠體量子點(diǎn);(d) 立方八面體的表面原子展開圖
研究表明,在使用PbO為前驅(qū)體,油酸(Oleic Acid,OA)為配體,制備量子點(diǎn)的過程中,羥基的存在有利于PbS量子點(diǎn)(111)晶面的形成和穩(wěn)定[54];但羥基對于光伏器件而言,容易造成不利影響[48]。Cao等[48]認(rèn)為,表面鈍化成為基于PbS量子點(diǎn)的太陽能電池高性能的關(guān)鍵;但液相配體交換過程中,PbS量子點(diǎn)表面不可避免地存在羥基配體。目前,對基于PbS的太陽能電池而言,使用鹵素[4]進(jìn)行陰離子置換PbS量子點(diǎn)表面的羥基,使PbS膠體量子點(diǎn)表面鈍化,成為提高PbS太陽能電池穩(wěn)定性和轉(zhuǎn)換率的重要手段。
對于制備好的含有PbS膠體量子點(diǎn)的光電器件,在器件完成時(shí),及時(shí)在惰性氣氛下對器件封裝,隔絕環(huán)境中的O2和H2O,也是提升穩(wěn)定性的有效手段。
因H2O中的O2和羥基會(huì)降低PbS膠體量子點(diǎn)的穩(wěn)定性,從穩(wěn)定性角度出發(fā),水溶性PbS膠體量子點(diǎn)制備好后,應(yīng)盡快使用,以縮短PbS膠體量子點(diǎn)體系在H2O中的保存時(shí)間;或者制備出油溶性PbS膠體量子點(diǎn),在用于水溶性環(huán)境時(shí),再通過配體置換將油溶性PbS膠體量子點(diǎn)改性為水溶性的。量子點(diǎn)的配體交換可以在固相或溶液中進(jìn)行,如果需要將表面配體替換為碳鏈更短、導(dǎo)電性更強(qiáng)的配體,則配體交換通常在量子點(diǎn)薄膜中進(jìn)行[55]。
隨著鈣鈦礦研究的不斷深入,Beygi等[49]發(fā)現(xiàn),PbS量子點(diǎn)經(jīng)鈣鈦礦配體處理后具有較高的氧化穩(wěn)定性,而鈣鈦礦在空氣環(huán)境中則部分氧化生成PbO和PbCO3組分。
綜上所述,不同領(lǐng)域解決PbS膠體量子點(diǎn)穩(wěn)定性的技巧有所差異,但可以將其制備、保存及應(yīng)用全過程的多個(gè)增強(qiáng)穩(wěn)定性的技巧結(jié)合起來,共同發(fā)揮作用。
PbS膠體量子點(diǎn)因其制備成本低廉、方法簡單、可調(diào)諧波段涵蓋多個(gè)應(yīng)用領(lǐng)域的優(yōu)點(diǎn)在發(fā)光二極管、生物成像、太陽能電池、紅外探測器等方面具有很強(qiáng)的實(shí)用價(jià)值,但穩(wěn)定性限制了其在這些領(lǐng)域的深入推廣。本文對PbS膠體量子點(diǎn)穩(wěn)定性的研究進(jìn)行了總結(jié),并討論P(yáng)bS膠體量子點(diǎn)從制備、保存、應(yīng)用等多個(gè)環(huán)節(jié)提升穩(wěn)定性的可能方法及機(jī)理。最終提出根據(jù)實(shí)際應(yīng)用領(lǐng)域采用多種方法相結(jié)合,整體提升PbS膠體量子點(diǎn)穩(wěn)定性的思路。
[1] ZHAO Y, YANG S, ZHAO J, et al. PbS quantum dots based organic-inorganic hybrid infrared detecting and display devices[J]., 2017, 196: 176-178.
[2] HOU B, CHO Y, Kim B S, et al. Highly monodispersed PbS quantum dots for outstanding cascaded-junction solar cells[J]., 2016, 1(4): 834-839.
[3] ZHANG B, LI G, ZHANG J, et al. Synthesis and characterization of PbS nanocrystals in water/C12E9/cyclohexane microemulsions[J]., 2003, 14(4): 443-446.
[4] YANG X, YANG J, KHAN J, et al. Hydroiodic acid additive enhanced the performance and stability of PbS-QDs solar cells via suppressing hydroxyl ligand[J]., 2020, 12(1): 37.
[5] CHUANG C H, Brown P R, Bulovic V, et al. Improved performance and stability in quantum dot solar cells through band alignment engineering[J]., 2014, 13(8): 796-801.
[6] Shrestha A, Batmunkh M, Tricoli A, et al. Near-infrared active lead chalcogenide quantum dots: preparation, post-synthesis lig and exchange, and applications in solar cells[J]., 2019, 58(16): 5202-5224.
[7] Tavakoli Dastjerdi H, Tavakoli R, Yadav P, et al. Oxygen plasma-induced p-type doping improves performance and stability of PbS quantum dot solar cells[J]., 2019, 11(29): 26047-26052.
[8] LIN Q, YUN H J, LIU W, et al. Phase-transfer ligand exchange of lead chalcogenide quantum dots for direct deposition of thick, highly conductive films[J]., 2017, 139(19): 6644-6653.
[9] De Iacovo A, Venettacci C, Colace L, et al. PbS colloidal quantum dot photodetectors operating in the near infrared[J], 2016, 6: 37913.
[10] Venettacci C, Martin-Garcia B, Prato M, et al. Increasing responsivity and air stability of PbS colloidal quantum dot photoconductors with iodine surface ligands[J]., 2019, 30(40): 405204.
[11] Georgitzikis E, Malinowski P E, Li Y, et al. Integration of PbS quantum dot photodiodes on silicon for NIR imaging[J]., 2020, 20(13): 6841-6848.
[12] CHEN W, TANG H, CHEN Y, et al. Spray-deposited PbS colloidal quantum dot solid for near-infrared photodetectors[J]., 2020, 78: 105254.
[13] Ahn S, CHUNG H, CHEN W, et al. Optoelectronic response of hybrid PbS-QD/graphene photodetectors[J]., 2019, 151(23): 234705.
[14] SUN L, Choi J J, Stachnik D, et al. Bright infrared quantum-dot light-emitting diodes through inter-dot spacing control[J]., 2012, 7(6): 369-373.
[15] Shirasaki Y, Supran G J, Bawendi M G, et al. Emergence of colloidal quantum-dot light-emitting technologies[J]., 2013, 7(1): 13-23.
[16] Zaini M S, Liew J Y C, Alang Ahmad S A, et al. Photoluminescence investigation of carrier localization in colloidal PbS and PbS/MnS quantum dots[J]., 2020, 5(48): 30956-30962.
[17] Pradhan S, Di Stasio F, Bi Y, et al. High-efficiency colloidal quantum dot infrared light-emitting diodes via engineering at the supra-nanocrystalline level[J]., 2019, 14(1): 72-79.
[18] LIU H, ZHONG H, ZHENG F, et al. Near-infrared lead chalcogenide quantum dots: Synthesis and applications in light emitting diodes[J]., 2019, 28(12): 128504.
[19] Imamura Y, Yamada S, Tsuboi S, et al. Near-infrared emitting PbS quantum dots for in vivo fluorescence imaging of the thrombotic state in septic mouse brain[J]., 2016, 21(8): 1080.
[20] Benayas A, Ren F, Carrasco E, et al. PbS/CdS/ZnS quantum dots: A multifunctional platform for in vivo near-infrared low-dose fluorescence imaging[J]., 2015, 25(42): 6650-6659.
[21] Raissi M, Sajjad M T, Pellegrin Y, et al. Size dependence of efficiency of PbS quantum dots in NiO-based dye sensitised solar cells and mechanistic charge transfer investigation[J]., 2017, 9(40): 15566-15575.
[22] Cademartiri L, Bertolotti J, Sapienza R, et al. Multigram scale, solventless, and diffusion-controlled route to highly monodisperse PbS nanocrystals[J]., 2006, 110(2): 671-673.
[23] ZHOU S, LIU Z, WANG Y, et al. Towards scalable synthesis of high-quality PbS colloidal quantum dots for photovoltaic applications[J].., 2019, 7(6): 1575-1583.
[24] Moreels I, Lambert K, Smeets D, et al. Size-dependent optical properties of colloidal PbS quantum dots[J]., 2009, 3(10): 3023-3030.
[25] ZHANG J, Crisp R W, GAO J, et al. Synthetic conditions for high-accuracy size control of PbS quantum dots[J]., 2015, 6(10): 1830-1833.
[26] ?apek R K, Lambert K, Dorfs D, et al. Synthesis of extremely small CdSe and bright blue luminescent CdSe/ZnS nanoparticles by a prefocused hot-injection approach[J]., 2009, 21(8): 1743-1749.
[27] KUO Y C, WANG Q, Ruengruglikit C, et al. Antibody-conjugated CdTe quantum dots for escherichia coli detection[J]., 2008, 112(13): 4818-4824.
[28] MAO X, YU J, XU J, et al. Enhanced performance of all solid-state quantum dot-sensitized solar cells via synchronous deposition of PbS and CdS quantum dots[J]., 2020, 44(2): 505-512.
[29] Skurlov I D, Korzhenevskii I G, Mudrak A S, et al. Optical properties, morphology, and stability of iodide-passivated lead sulfide quantum dots[J]., 2019, 12(19): 3219.
[30] Beygi H, Sajjadi S A, Babakhani A, et al. Surface chemistry of as-synthesized and air-oxidized PbS quantum dots[J]., 2018, 457: 1-10.
[31] Choi H, Ko J H, Kim Y H, et al. Steric-hindrance-driven shape transition in PbS quantum dots: understanding size-dependent stability[J].., 2013, 135(14): 5278-5281.
[32] Kagan C R, Murray C B. Charge transport in strongly coupled quantum dot solids[J]., 2015, 10(12): 1013-1026.
[33] Kim S, Noh J, Choi H, et al. One-step deposition of photovoltaic layers using iodide terminated PbS quantum dots[J]., 2014, 5(22): 4002-4007.
[34] Shuklov I A, Toknova V F, Lizunova A A, et al. Controlled aging of PbS colloidal quantum dots under mild conditions[J]., 2020, 18: 100357.
[35] ZHANG Y, Zherebetskyy D, Bronstein N D, et al. Molecular oxygen induced in-gap states in PbS quantum dots[J]., 2015, 9(10): 10445-10452.
[36] Ushakova E V, Cherevkov S A, Litvin A P, et al. Ligand-dependent morphology and optical properties of lead sulfide quantum dot superlattices[J]., 2016, 120(43): 25061-25067.
[37] Weidman M C, Beck M E, Hoffman R S, et al. Monodisperse, air-stable PbS nanocrystals via precursor stoichiometry control[J]., 2014, 8(6): 6363-6371.
[38] ZHAO H, LIANG H, Vidal F, et al. Size dependence of temperature-related optical properties of PbS and PbS/CdS core/shell quantum dots[J]., 2014, 118(35): 20585-20593.
[39] LIU J, ZHANG H, Navarro-Pardo F, et al. Hybrid surface passivation of PbS/CdS quantum dots for efficient photoelectrochemical hydrogen generation[J]., 2020, 530: 147252.
[40] Tsukasaki Y, Morimatsu M, Nishimura G, et al. Synthesis and optical properties of emission-tunable PbS/CdS core–shell quantum dots for in vivo fluorescence imaging in the second near-infrared window[J], 2014, 4(77): 41164-41171.
[41] Nasilowski M, Nienhaus L, Bertram S N, et al. Colloidal atomic layer deposition growth of PbS/CdS core/shell quantum dots[J]., 2017, 53(5): 869-872.
[42] Maulu A, Navarro-Arenas J, Rodriguez-Canto P J, et al. Charge transport in trap-sensitized infrared PbS quantum-dot-based photoconductors: pros and cons[J]., 2018, 8(9): 677.
[43] CAO J, ZHU H, DENG D, et al. In vivo NIR imaging with PbS quantum dots entrapped in biodegradable micelles[J]., 2012, 100(4): 958-968.
[44] DENG D, CAO J, XIA J, et al. Two-phase approach to high-quality, oil-soluble, near-infrared-emitting PbS quantum dots by wsing various water-soluble anion precursors[J]., 2011, 2011(15): 2422-2432.
[45] Abel K A, Shan J, Boyer J-C, et al. Highly photoluminescent PbS nanocrystals: The beneficial effect of trioctylphosphine[J]., 2008, 20(12): 3794-3796.
[46] Moreels I, Justo Y, De Geyter B, et al. Size-tunable, bright, and stable PbS quantum dots: a surface chemistry study[J]., 2011, 5(3): 2004-2012.
[47] Steckel J S, Yen B K, Oertel D C, et al. On the mechanism of lead chalcogenide nanocrystal formation[J]., 2006, 128(40): 13032-13033.
[48] CAO Y, Stavrinadis A, Lasanta T, et al. The role of surface passivation for efficient and photostable PbS quantum dot solar cells[J]., 2016, 1(4): 16035.
[49] Beygi H, Sajjadi S A, Babakhani A, et al. Air exposure oxidation and photooxidation of solution-phase treated PbS quantum dot thin films and solar cells[J]., 2019, 203: 110163.
[50] Pichaandi J, van Veggel F C J M. Near-infrared emitting quantum dots: Recent progress on their synthesis and characterization[J]., 2014, 263-264: 138-150.
[51] Boercker J E, Woodall D L, Cunningham P D, et al. Synthesis and characterization of PbS/ZnS core/shell nanocrystals[J]., 2018, 30(12): 4112-4123.
[52] Speirs M J, Balazs D M, Fang H H, et al. Origin of the increased open circuit voltage in PbS–CdS core–shell quantum dot solar cells[J]., 2015, 3(4): 1450-1457.
[53] WANG Z, HU Z, Kamarudin M A, et al. Enhancement of charge transport in quantum dots solar cells by N-butylamine-assisted sulfur-crosslinking of PbS quantum dots[J]., 2018, 174: 399-408.
[54] Zherebetskyy D, Scheele M, Zhang Y, et al. Hydroxylation of the surface of PbS nanocrystals passivated with oleic acid[J]., 2014, 344(6190): 1380-1384.
[55] GU M, WANG Y, YANG F, et al. Stable PbS quantum dot ink for efficient solar cells by solution-phase ligand engineering[J]., 2019, 7(26): 15951-15959.
Research Progress on Stability of PbS Colloidal Quantum Dots
ZHAO Yiqun1,WU Zhenfen2,YANG Xiaojie1,DENG Dazheng3,LIU Xue’e1,ZHOU Huiqun1
(1. School of Architectural Engineering,Kunming Metallurgy College, Kunming 650033, China;2. Kunming University of Science and Technology, Kunming 650023, China; 3. Kunming Institute of Physics, Kunming 650223, China)
Due to the simple preparation, low cost, and adjustable bandgap via changing their sizes in the near-infrared band, PbS colloidal quantum dots (QDs) have been widely used in many fields such as solar cell, infrared detection, LED, and biological imaging. However, instability limits further practical application. In this study, the instability mechanism of PbS colloidal QDs was investigated, and measures to improve their stability are discussed in terms of preparation, structure, preservation, and application. Measures and mechanisms for further improving stability are proposed, which have great value for their application and development.
PbS colloidal QDs, applications of colloidal QDs, stability, core-shell structure
O434.3
A
1001-8891(2022)03-0205-07
2021-04-19;
2021-08-20.
趙逸群(1980-),男,博士,研究方向是光電材料。
吳楨芬(1981-),女,副教授,碩士生導(dǎo)師,主要從事化學(xué)與電路研究。E-mail:bitzhaoyq@163.com。
云南省教育廳科學(xué)研究基金項(xiàng)目(2018JS550);昆明理工大學(xué)分析測試基金(2020T20060036)。