施淋楓，袁皓，孟祥川,2，胡笑添,2，陳義旺,2,3

大面積柔性有機(jī)太陽電池：器件設(shè)計(jì)與印刷技術(shù)

施淋楓1，袁皓1，孟祥川1,2，胡笑添1,2，陳義旺1,2,3

（1.北京大學(xué)長三角光電科學(xué)研究院，江蘇 南通 226010；2.南昌大學(xué) 化學(xué)化工學(xué)院/高分子及能源化學(xué)研究院（IPEC），南昌 330031；3.江西師范大學(xué) 高等研究院/氟硅能源材料與化學(xué)教育部重點(diǎn)實(shí)驗(yàn)室，南昌 330022）

為研究者提供OSCs制造技術(shù)相關(guān)的全面見解和最新進(jìn)展，分析現(xiàn)有的技術(shù)瓶頸和無法解決的規(guī)模效率損失，以獲得可擴(kuò)展和可打印的大面積光伏組件。從功能層材料的選擇、印刷工藝研究現(xiàn)狀和大面積效率損失等方面展開綜述，重點(diǎn)闡述柔性高效大面積有機(jī)光伏器件印刷制備的技術(shù)難題。文中將進(jìn)一步推動可印刷有機(jī)半導(dǎo)體材料在下一代清潔能源中的集成應(yīng)用，并在可穿戴電子、光伏建筑一體化和物聯(lián)網(wǎng)等應(yīng)用領(lǐng)域引起廣泛關(guān)注。

有機(jī)光伏電池；模組化設(shè)計(jì)；柔性器件；印刷技術(shù)

與傳統(tǒng)光伏器件相比，可柔性是有機(jī)太陽電池（OSCs）最突出的優(yōu)勢，其顯示出巨大的商業(yè)潛能。目前已有研究工作者在界面/活性層合成，器件結(jié)構(gòu)設(shè)計(jì)，透明電極修飾和印刷技術(shù)創(chuàng)新等領(lǐng)域開展廣泛研究，單結(jié)OSCs的最大光電轉(zhuǎn)換效率（PCE）已超過19%，符合商業(yè)化應(yīng)用標(biāo)準(zhǔn)，但印刷技術(shù)的合理選擇、大面積印刷的性能損失和柔性組件的結(jié)構(gòu)設(shè)計(jì)仍然是限制柔性O(shè)SCs商業(yè)化的瓶頸。關(guān)于可印刷柔性大面積OSCs的打印技術(shù)/功能材料以及光伏組件的效率損失分析的最新進(jìn)展，目前還沒有詳細(xì)的綜述。文中綜述柔性有機(jī)太陽電池（OSCs）和組件（OSMs）的各種印刷技術(shù)、性能損失和模塊化設(shè)計(jì)的最新研究進(jìn)展，為可印刷和大規(guī)模有機(jī)半導(dǎo)體材料提供了一站式參考。

1 簡介

與晶體硅太陽電池和基于無機(jī)半導(dǎo)體材料的薄膜太陽電池相比，有機(jī)太陽電池（Organic Solar Cells，OSCs）具有質(zhì)輕、價廉、可溶液加工和可柔性等諸多優(yōu)點(diǎn)，在可穿戴電子設(shè)備的集成設(shè)計(jì)和與卷對卷（Roll-to-Roll，R2R）大面積印刷技術(shù)的適應(yīng)性上表現(xiàn)出巨大潛能[1-5]。近年來，隨著有機(jī)光伏材料和器件結(jié)構(gòu)的飛速創(chuàng)新，通過旋涂法制備的剛性O(shè)SCs的功率轉(zhuǎn)換效率（Power Conversion Efficiency，PCE）有了明顯提高，目前最佳PCE值已達(dá)到19%以上，這說明了其已具有一定的商業(yè)化價值[6-12]。此外，隨著各種R2R印刷方法的發(fā)展和研究的深入，印刷OSCs的PCE也已接近17%，這進(jìn)一步驗(yàn)證了溶液印刷光電器件的可行性[13-17]，因此，柔性可印刷OSCs在可穿戴能源、便攜式電子設(shè)備和異形顯示設(shè)備中具有廣闊的應(yīng)用前景，這引起了人們的廣泛關(guān)注。

圖1顯示了柔性O(shè)SCs的器件結(jié)構(gòu)以及基于剛性和柔性襯底、大面積和小面積襯底的OSCs的PCE值發(fā)展趨勢[13,15,18-100]。如圖1a所示，常規(guī)的OSCs器件一般包括頂部背電極層、p型有機(jī)半導(dǎo)體給體材料和n型有機(jī)半導(dǎo)體受體材料組成的光敏層，以及底部透明電極層，同時，為了保證足夠的電荷收集和傳輸，在透明電極層/背電極層與光敏層之間常使用兩層緩沖層材料[101-102]，因此，需要從上述5層中優(yōu)化OSCs的整體機(jī)械力學(xué)穩(wěn)定性（包括耐彎折、耐拉伸、扭轉(zhuǎn)、皮膚親和性等）。首先，柔性透明電極會顯著影響OSCs的光電性能和力學(xué)穩(wěn)定性。完美的透明電極需要具備以下特點(diǎn)：理想的方塊電阻、合適的透光率、光滑的表面粗糙度、足夠的機(jī)械強(qiáng)度和良好的熱穩(wěn)定性[103-107]。然而，當(dāng)前高效OSCs的透明電極通常是脆性的氧化銦錫（Indium Tin Oxide，ITO）材料，該材料不符合柔性O(shè)SCs的制備要求。因此，為了能找到在極端彎曲條件下有良好綜合性能的柔性透明電極，人們在制備ITO電極替代品方面做了許多研究工作，在這些替代品中，最具代表性材料有銀納米線或網(wǎng)格、超薄金屬層、碳基材料和導(dǎo)電聚合物等[72,107-118]。另外，OSCs光電性能的進(jìn)一步優(yōu)化還取決于高性能耐彎折緩沖層和光敏層材料的發(fā)展。因出色的空穴和電子選擇和收集能力，聚（3,4–乙二氧噻吩）∶聚（苯乙烯磺酸鹽）（PEDOT∶PSS）陽極緩沖層和聚電解質(zhì)陰極緩沖層是最常用于柔性O(shè)SCs的材料[72,119-127]。此外，具有光伏性能可設(shè)計(jì)性和厚度不敏感性的新型給體/受體材料的分子設(shè)計(jì)和合成為柔性O(shè)SCs的發(fā)展提供了必要的基礎(chǔ)[6,7,9,10,12,31,61-78]。迄今為止，柔性O(shè)SCs的最佳PCE值已超過16%（基于柔性銀納米線襯底），該P(yáng)CE已初步達(dá)到了光伏器件商業(yè)化的最低標(biāo)準(zhǔn)[74]?？傊M(jìn)一步開發(fā)高性能緩沖層和具有理想柔性、環(huán)境穩(wěn)定性、最佳形貌和相分離結(jié)構(gòu)的光敏層材料對于發(fā)展柔性O(shè)SCs來說仍有重要意義[128-139]。

圖1 有機(jī)太陽電池結(jié)構(gòu)及性能

為了滿足OSCs長遠(yuǎn)應(yīng)用的實(shí)際需求，相應(yīng)的大面積器件制備工藝也很重要。與發(fā)展較好的小面積OSCs的相比，各種R2R印刷技術(shù)制備的大面積OSCs效率損失顯著，尤其是在柔性襯底上[75,77,140-144]。2009年，Krebs等[145-147]總結(jié)了不同制備OSCs的成膜方法，他們指出旋涂技術(shù)不適合大規(guī)模柔性O(shè)SCs的生產(chǎn)，并介紹了一系列用來制備柔性大面積OSCs的印刷技術(shù)。這些技術(shù)主要有半月板刮涂、狹縫擠出印刷、凹版印、絲網(wǎng)印刷、噴墨打印等。最近，Li等[148]報(bào)道了一種高效的順序沉積制備準(zhǔn)平面異質(zhì)結(jié)OSCs的方法，即通過基于非鹵化溶劑體系的連續(xù)沉積來制備可印刷OSCs，獲得了16.77%的PCE值。Hou等[83]采用半月板刮涂技術(shù)，在1.0 cm2面積上基于鹵素或非鹵素溶劑體系制備的剛性O(shè)SCs效率達(dá)到15.5%或10.6%。Min等采用逐層刮涂的策略在PM6:Y6系統(tǒng)上制備OSCs，獲得了16.35%的PCE。此外，11.52 cm2的太陽電池組件獲得了11.86%的記錄性PCE，其幾何填充因子（Geometrical Fill Factor，GFF），也就是組件對于入射光的實(shí)際有效利用面積超過90%[81]。很容易發(fā)現(xiàn)，從實(shí)驗(yàn)室小規(guī)模制備到工業(yè)大面積生產(chǎn)，如何保持優(yōu)良的光伏特性一直是OSCs商業(yè)化轉(zhuǎn)變的致命弱點(diǎn)。因此，在旋涂或印刷過程中探索本體異質(zhì)結(jié)(BHJ) OSCs的形貌演化機(jī)制很有必要。Chen等[15]證實(shí)了通過狹縫擠出印刷制備可將柔性O(shè)SCs擴(kuò)展到大面積有機(jī)太陽電池組件（15 cm2），且不會造成明顯的性能損失。他們首先利用在旋涂和狹縫擠出印刷技術(shù)中的剪切沖量來調(diào)整富勒烯/非富勒烯OSCs體系有機(jī)光敏層的形貌演變，并獲得了狹縫擠出印刷和旋涂之間的定量剪切沖量轉(zhuǎn)換因子。與此同時，對于PTB7–Th:PC71BM和PBDB–T:ITIC光敏層，基于1.04 cm2的柔性狹縫擠出印刷OSCs的PCE分別達(dá)到9.10%和9.77%。在滿足機(jī)械穩(wěn)定性和制備重現(xiàn)性的前提下，15 cm2柔性有機(jī)太陽電池組件（Organic Solar Modules，OSMs）的效率可達(dá)8.90%。與小面積OSCs的制備相比，大面積OSCs印刷制備過程中的形貌演化控制規(guī)律和印刷技術(shù)都發(fā)生了變化，因此有必要對基于各種印刷方法制備的柔性大面積光電器件進(jìn)行全面回顧。

文中綜述了大面積OSCs的研究現(xiàn)狀和高效印刷制備方式的發(fā)展現(xiàn)狀，主要集中在以下兩方面。

1）用于大面積印刷制備的柔性有機(jī)光伏材料。為了實(shí)現(xiàn)OSCs和OSMs的高質(zhì)量大面積印刷，形貌和相分離的可控性研究以及活性層的厚度不敏感設(shè)計(jì)是必不可少的，相關(guān)研究已被廣泛報(bào)道，包括富勒烯受體體系、非富勒烯受體體系、全聚合物體系和三元共混體系等。

2）大面積制備OSCs的印刷方法。很多可大面積化的沉積制備技術(shù)已被證實(shí)可以用來制備OSCs或OSMs，這些技術(shù)主要包括半月板刮涂、狹縫擠出印刷、凹版印刷、絲網(wǎng)印刷、噴墨打印等?？傊?，通過結(jié)合以上兩點(diǎn)可以成功制備出低效率損失和高重現(xiàn)性的大面積柔性O(shè)SCs，這將有利于未來OSCs或OSMs的工業(yè)化制備和商業(yè)化發(fā)展。

2 高性能大面積OSCs的印刷制備思路

目前，具有優(yōu)異光電性能的OSCs制備方式通常是采用旋涂技術(shù)，這可確保光敏層形成納米級的互穿網(wǎng)絡(luò)結(jié)構(gòu)，同時在最佳效率條件下，光敏層的膜厚僅為110 nm左右，這些限制了柔性大面積OSCs的商業(yè)應(yīng)用。首先，光敏層形貌和相分離結(jié)構(gòu)的一致性會嚴(yán)重影響因等比例放大器件面積而導(dǎo)致的OSCs性能下降。然而，由于每種涂布/印刷方法都有其既定的操作模式，因此很難控制大面積BHJ薄膜的形貌和相分離結(jié)構(gòu)一致性。其次，目前高效給體/受體光敏層的綜合性能與膜厚有關(guān)，而商業(yè)化的R2R印刷技術(shù)還無法制備高精度的大面積納米級薄膜，這意味著其制備再現(xiàn)性較差。最后，結(jié)合上述關(guān)鍵問題，光敏層可能存在大量的點(diǎn)缺陷，這在粗糙度相對較高的柔性襯底（如銀納米線、銀網(wǎng)或ITO/PET透明電極等）上會加劇形貌劣化，從而導(dǎo)致器件效率不理想，因此，設(shè)計(jì)具有顯著成膜性能、厚度不敏感性的給體/受體材料以及探索旋涂工藝與R2R印刷技術(shù)之間的定量轉(zhuǎn)換關(guān)系，能幫助實(shí)現(xiàn)制備高質(zhì)量的柔性大面積OSCs或OSMs[149-151]。

以前的文獻(xiàn)中，人們?yōu)橛∷⒅苽涓咝阅躉SCs做了大量工作，包括調(diào)整光敏層結(jié)構(gòu)和合成對厚度不敏感的給體/受體材料。相分離結(jié)構(gòu)、相純度和給體/受體聚集程度組成的形貌決定了薄膜的質(zhì)量，可通過多種處理方法對其進(jìn)行優(yōu)化，例如三元共混設(shè)計(jì)、熱退火或溶劑–蒸汽處理等。上述優(yōu)化過程對于保持形貌一致性以實(shí)現(xiàn)大面積R2R印刷的高效厚膜器件具有重要意義[6-12,152-158]。除了形貌控制外，合成具有高載流子遷移率和低復(fù)合特性的新型給體/受體材料也適用于厚度不敏感性器件的制備[151]。其中一個有效的思路是將分子鏈做成face-on堆砌的分子排列結(jié)構(gòu)，這可以進(jìn)一步促進(jìn)載流子的梯度傳輸。在本節(jié)中，重點(diǎn)討論了大面積OSCs光敏層的形貌一致性控制，并簡要總結(jié)新型厚度不敏感性光敏層材料的設(shè)計(jì)[159]。通常，從旋涂OSCs到具有大面積光活性區(qū)域的印刷器件，可以觀察到明顯的效率損失，這已通過大量研究工作得到驗(yàn)證。造成這種現(xiàn)象的原因很復(fù)雜，例如：玻璃襯底和柔性襯底的形貌差異，針對大面積制備的不同印刷方法的適應(yīng)性，以及隨著器件尺寸的增加而導(dǎo)致成膜均勻性的變化等[159]?？傊?，主要原因在于不同器件面積、不同印刷方法制備的OSCs光敏層形貌一致性難以保證。形貌一致性包括2個方面，即內(nèi)部相分離結(jié)構(gòu)和活性層的薄膜厚度。

3 大面積制備的印刷技術(shù)及器件結(jié)構(gòu)設(shè)計(jì)

隨著剛性O(shè)SCs的PCE大幅提高至19%以上，大面積柔性O(shè)SCs和有機(jī)太陽電池組件（OSMs）已經(jīng)引起了研究人員的廣泛興趣和研究報(bào)道[12]。一般來說，旋涂工藝是制備OSCs的主要應(yīng)用技術(shù)，但旋涂工藝并不適合OSCs的大批量生產(chǎn)。因?yàn)殡S著旋涂制備OSCs有效面積的增大，活性層形貌和相分離會發(fā)生一些無意和非理想的退化，這些都會影響器件的整體性能。因此，針對高效剛性和柔性O(shè)SCs的大面積R2R印刷技術(shù)逐漸發(fā)展起來[4,5,13,15-17]。

考慮到生產(chǎn)效率和實(shí)際應(yīng)用，低溫印刷柔性O(shè)SCs的研究意義遠(yuǎn)高于剛性器件，這也是OSCs相對于無機(jī)太陽電池的優(yōu)勢所在。為了實(shí)現(xiàn)柔性O(shè)SCs的商業(yè)化生產(chǎn)，各種R2R打印方法已被廣泛探索和報(bào)道。然而，目前還沒有標(biāo)準(zhǔn)且優(yōu)秀的印刷技術(shù)來制備高效的大面積光電器件，因此開發(fā)合適的R2R印刷方法也是一個緊迫的挑戰(zhàn)[4-5,15]。根據(jù)印刷油墨是否與柔性襯底接觸，通常印刷/涂布技術(shù)可分為接觸式和非接觸式（圖2）[149-154,159-160]。其中刮涂、狹縫擠出印刷、凹版印刷、噴墨打印、絲網(wǎng)印刷、噴涂、平板刮涂、柔版印刷都是制備OSCs的有效印刷方法。Viana等[161]提出了印刷參數(shù)與薄膜質(zhì)量之間的聯(lián)系，將其應(yīng)用在柔性塑料襯底（PET、PEN、PI等）上制造印刷電子設(shè)備，并介紹了薄膜質(zhì)量總是與表面潤濕性、粘附性和延展性有關(guān)。對于柔性塑料襯底來說，印刷薄膜的均勻性和成膜質(zhì)量較差是由于表面能量低，這個問題可以通過在印刷前進(jìn)行額外表面處理（UVO或PLASMA處理）來解決。因此，在感光層從濕潤狀態(tài)轉(zhuǎn)變?yōu)楣虘B(tài)薄膜的過程中，控制早期材料聚集和相分離行為對其形貌演變非常重要。然而，選擇一個特定的印刷參數(shù)來確定不同印刷/涂布方法之間的內(nèi)在關(guān)系是不切實(shí)際的。Chen等[15]報(bào)道了通過計(jì)算沖量積累并采用旋涂工藝和狹縫擠出印刷方法制備富勒烯和非富勒烯受體體系OSCs光敏層形貌演變機(jī)制的研究工作。通過形貌、分子構(gòu)象測試以及粗?；肿觿恿W(xué)模擬，他們發(fā)現(xiàn)了基于剪切沖量累積量的不同沉積方式下光敏層形貌和相分離之間的明顯關(guān)系。他們進(jìn)一步研究了不同印刷方式下的光敏層形貌一致性，驗(yàn)證了旋涂和狹縫擠出印刷之間剪切沖量的定量轉(zhuǎn)換系數(shù)，發(fā)現(xiàn)該系數(shù)可適用于各種OSCs體系。

3.1 半月板刮涂

半月板刮涂是制備高效OSCs的有效方法，可初步替代旋涂技術(shù)（圖3）[13-16,83,92]。半月板涂覆工藝是利用半月板的水平位移將油墨涂覆在剛性或柔性襯底上，從而得到納米或微米厚度的薄膜。有機(jī)薄膜的印刷質(zhì)量可以通過控制半月板與印刷襯底的距離、襯底的表面能和半月板的位移率來實(shí)現(xiàn)。其中，半月板與印刷襯底的距離對薄膜厚度有直觀的影響，半月板液面的連續(xù)存在也可以保證印刷過程的順利進(jìn)行。襯底的表面能會調(diào)節(jié)襯底材料上油墨的潤濕性，這不僅對薄膜厚度有影響，而且對薄膜質(zhì)量有巨大影響。半月板涂布速度（）對薄膜厚度（）的影響是復(fù)雜的，它們之間的主要關(guān)系遵循兩種模型。第一個是蒸發(fā)模型，它要求半月板涂層速度小于4 mm/s，log()與log()的斜率約為?0.97。在該模型中，半月板離開油墨表面后，印刷油墨會迅速變干，半月板與襯底之間的溶劑蒸發(fā)決定了光敏層溶液的沉積質(zhì)量。當(dāng)半月板刮涂速度大于20 mm/s時，涂布過程遵循Landau?Levich模型。在這種模式下，log()與log()的斜率約為0.65，由于半月板刮涂速度非?？?，印刷油墨并未完全變干（圖3d）。因此，需要一個額外的處理來確保薄膜質(zhì)量[162]。除了設(shè)備參數(shù)需要調(diào)整外，油墨的表面張力、黏度等流變性能對最終成膜質(zhì)量也有明顯影響。干燥后的薄膜最終厚度可以通過下式計(jì)算。

圖2 OSCs當(dāng)前主流的印刷制備方法

(1)

式中：為薄膜厚度；為半月板與襯底之間的距離；為印刷油墨的濃度；為干燥薄膜的密度。

2008年，Mens等[163]首次報(bào)道了采用MDMO– PPV:PC61BM體系的光敏層通過半月板刮涂工藝制備OSCs。在相同的油墨條件下，半月板涂層薄膜中的PC61BM顯示出比旋涂薄膜中更高的結(jié)晶度，這與固態(tài)核磁共振表征結(jié)果相一致。這一結(jié)果表明，由于溶劑的快速蒸發(fā)過程，與半月板涂層薄膜相比，旋涂薄膜可能不完全適用于熱力學(xué)平衡規(guī)律。利用這一特殊現(xiàn)象，Ma等[83]通過半月板刮涂制備OSCs，證實(shí)光敏層內(nèi)給體和受體材料的平衡結(jié)晶性。結(jié)合三元共混策略，基于PBDB–T：PTB7–Th：FOIC的光電器件PCE值達(dá)到12.02%。2018年，Hou等[43]通過半月板涂覆工藝，用環(huán)保溶劑（四氫呋喃/異丙醇和鄰二甲苯/1–苯基萘）制備了高效的OSCs，基于PBTA–TF:IT–M體系可以獲得11.7%的優(yōu)異PCE。同時，當(dāng)器件尺寸增加到1 cm2時，基于半月板刮涂的THF/IPA主溶劑的OSCs獲得了10.6%的PCE。此外，他們通過共聚聚合物合成了一種效率超過15%的給體材料。因?yàn)樵摴簿畚镒顑?yōu)化的溶解度，基于環(huán)境友好型溶液（THF）的半月板刮涂的光電器件達(dá)到了令人印象深刻的13.1%的PCE。他們還為OSCs設(shè)計(jì)了陰極緩沖層材料（NDI–N和NDI–Br），采用NDI–N作為緩沖層，用半月板刮涂工藝制備的1 cm2大面積OSCs器件實(shí)現(xiàn)了13.2%的PCE[92]。最近，Min等[13]報(bào)道了幾項(xiàng)關(guān)于通過半月板刮涂工藝制備的具有雙層結(jié)構(gòu)的平面異質(zhì)結(jié)高效OSCs的研究工作。他們提出，由于復(fù)雜的形貌控制規(guī)律，本體異質(zhì)結(jié)結(jié)構(gòu)不適合大面積的OSCs批量制備。相比之下，雙層結(jié)構(gòu)具有許多獨(dú)特的特點(diǎn)，包括可控的“p-i-n”形態(tài)、良好的電荷傳輸和提取性能以及良好的普適性。結(jié)合半月板刮涂工藝，基于PM6∶Y6系統(tǒng)的逐層OSCs的最佳PCE達(dá)到16.35%。更重要的是，他們制備了11.52 cm2的OSMs，其幾何填充因子約為90%，最佳PCE值為11.86%（圖3a）。最近，Li等[148]報(bào)告了通過非鹵化溶劑連續(xù)沉積的分級體異質(zhì)結(jié)策略來制造高質(zhì)量的OSCs。通過這種方式，空氣環(huán)境中半月板刮涂的OSCs實(shí)現(xiàn)了16.77%的高PCE。

a 基于逐層（LbL）的大面積太陽組件的工藝流程 b 有效面積為11.52 cm2的太陽組件圖像[13] c 帶DIO的BHJ、無DIO的G-BHJ和帶DIO時G-BHJ在整個薄膜中聚合物重量含量的變化[148] d 使用葉片涂層NDI-N作為緩沖層的器件J-V和外部量子效率（EQE）曲線[92] e 薄膜厚度與半月板刮涂速度的關(guān)系 f 墨滴在疏水襯底上干燥時收縮和表面活性劑釘扎效應(yīng)[162]

與旋涂器件相比，除了OSCs相對樂觀的效率外，半月板刮涂還有一個最突出的優(yōu)勢，那就是節(jié)省原材料。一般來說，旋涂OSCs需要40～55 μL的光敏層溶液來滿足器件的制備，而半月板涂層只需要7～9 μL。對于未來商業(yè)化生產(chǎn)的OSCs來說，降低材料損耗是非常重要的。值得注意的是，半月板刮涂中的溶劑蒸發(fā)率也遠(yuǎn)低于旋涂處理中的溶劑蒸發(fā)率。這種緩慢的成膜過程可能會導(dǎo)致光敏層中給體和受體過度聚集或結(jié)晶[164]。因此，調(diào)節(jié)并合理適當(dāng)利用這一現(xiàn)象很有必要（圖3d）。

3.2 狹縫擠出印刷

狹縫擠出印刷也是一種印刷高效大面積OSCs的有效方法，它被認(rèn)為是有機(jī)光電器件R2R生產(chǎn)最具前景的方法（圖4）[165-171]。通過精密控制，狹縫擠出設(shè)備可連續(xù)印刷多層圖紋的剛性或柔性O(shè)SCs，這就減少了多次刻蝕過程，簡化了制備步驟，因此非常適合大面積OSCs的生產(chǎn)。在印刷過程中，油墨通過壓力槽或輸液泵被擠入槽頭，在此進(jìn)行圖案化和預(yù)成型階段。因此，適當(dāng)控制進(jìn)料速度、槽間距、圖案精度和印刷定位精度非常重要。與半月板刮涂工藝類似，狹縫擠出印刷也需要注意模頭與襯底之間的距離以及模頭或襯底的移動速度。只要上述參數(shù)能被嚴(yán)格控制，狹縫擠出印刷將是一項(xiàng)具有高度自動化的優(yōu)秀技術(shù)。狹縫擠出印刷工藝的原理圖和實(shí)物照片如圖4a所示，模頭是槽模設(shè)備中最重要的部件，它需要具備耐腐蝕、抗氧化、精度高等特點(diǎn)。膜厚控制也是值得進(jìn)一步探討的問題，它會在模頭中受到印刷油墨預(yù)成膜的影響。預(yù)成膜與槽距（0.2～100 mm）和油墨黏度（1～20 Pa·s）有關(guān)，因此油墨流變性與設(shè)備參數(shù)的協(xié)調(diào)控制成為生產(chǎn)高質(zhì)量薄膜的關(guān)鍵[4,62,165]。同時，狹縫擠出印刷為薄膜提供了一個緩慢的干燥過程，對其內(nèi)部結(jié)構(gòu)的形態(tài)和相分離調(diào)節(jié)處理是必不可免的。狹縫擠出印刷制備的干膜厚度可由下式計(jì)算。

(2)

式中：為干膜厚度；為進(jìn)料速度；為膠帶速度；為襯底寬度；為印刷油墨中的固體含量；為干膜密度。

2011年，Zimmermann等[167]通過狹縫擠出印刷技術(shù)制備了基于P3HT：PCBM系統(tǒng)的柔性O(shè)SCs，其PCE為0.64%。后來，Tan等[166]結(jié)合狹縫擠出印刷技術(shù)，在PV2000和PCBM系統(tǒng)上實(shí)現(xiàn)了全溶液和環(huán)境可加工有機(jī)光伏組件的PCE為7.56%。2017年，Bao等[85]證明了一種光敏層設(shè)計(jì)，該光敏層包括大面積、利用給體和受體之間具有合適的相分離結(jié)構(gòu)的溶液處理的全聚合物OSCs。通過使用不同結(jié)晶度的光敏層材料（給體和受體），他們驗(yàn)證了給體和受體的微相分離域的尺寸與共軛聚合物的結(jié)晶度成反比。由于這一特殊現(xiàn)象，通過狹縫擠出印刷工藝制備了大面積（10 cm2）的全聚合物OSCs，并實(shí)現(xiàn)了5%的PCE。Russell等[168]報(bào)道了一種高效的狹縫擠出印刷全聚合物OSCs，其活性層為PTzBI∶N2200系統(tǒng)，PCE高達(dá)9.1%，這是狹縫擠出印刷全聚合物OSCs的最佳效率。此外，Vak等[169]開發(fā)了一種用于OSCs的溫控狹縫擠出印刷技術(shù)，并研究了襯底和溶液溫度對器件性能、薄膜形態(tài)、分子結(jié)構(gòu)和載流子輸運(yùn)的影響。當(dāng)使用溫度為120 ℃和90 ℃的熱襯底和溶液，他們制備了剛性和柔性O(shè)SCs，PCE分別為10.0%和7.0%。2019年，Min等[170]使用PBDB-T-SF∶IT-4F體系作為狹縫擠出印刷的OSCs的光敏層，并在剛性襯底上實(shí)現(xiàn)了12.9%的PCE，與旋涂或半月板刮涂工藝相比，其PCE更高。同時，通過狹縫擠出印刷技術(shù)制造的基于柔性襯底的OSCs和OSMs效率分別達(dá)到12%和9%以上，這表明該大面積生產(chǎn)技術(shù)的可行性。最近，為了探索在不同模具溫度和襯底溫度下的聚集和結(jié)晶演化，Ma等[171]在狹縫擠出印刷過程中對PM7∶IT4F系統(tǒng)進(jìn)行了原位測量。由于改善了激子解離、電荷傳輸和抑制了非輻射電荷重組，在60 ℃模具溫度和60 ℃襯底溫度下，OSCs獲得13.2%的PCE值。

雖然狹縫擠出印刷可能是最適合OSCs商業(yè)化生產(chǎn)的印刷技術(shù)，但在實(shí)際應(yīng)用過程中仍有許多問題有待解決。首先是制備重現(xiàn)性性，目前對于高質(zhì)量薄膜的大規(guī)模生產(chǎn)，狹縫擠出印刷仍有困難，大部分的研究報(bào)告顯示，可通過在印刷薄膜上選擇高質(zhì)量的區(qū)域來制備光電器件，但連續(xù)且一致的高效制備技術(shù)還沒有實(shí)現(xiàn)。因此，加深對薄膜形貌和相分離調(diào)控的理解是必要的，這對柔性O(shè)SCs的商業(yè)化發(fā)展至關(guān)重要。其次是對新的制備技術(shù)的探索，在以前的報(bào)道中，一些成熟的技術(shù)如熱印刷和閃蒸干燥以及新穎的器件結(jié)構(gòu)如雙層印刷工藝是非常實(shí)用的，因此，應(yīng)該嘗試更多優(yōu)秀的方法來制備基于狹縫擠出印刷工藝的OSCs，這對于發(fā)展完美的狹縫擠出印刷技術(shù)也是非常重要的。

3.3 模組化OSCs的R2R印刷技術(shù)

R2R印刷技術(shù)一種特殊的印刷技術(shù)，已廣泛應(yīng)用于工業(yè)用品、塑料、玻璃、金屬片、陶瓷片、電子板等的制備。印刷油墨的高效率和高質(zhì)量成膜特性使R2R印刷能夠連續(xù)制備有機(jī)薄膜。一般來說，一個完整的R2R印刷技術(shù)由多個部件組成，包括放卷區(qū)、放卷區(qū)、表面處理區(qū)、印模區(qū)、糾偏區(qū)、超聲波清洗區(qū)、退火區(qū)、電暈區(qū)、風(fēng)淋區(qū)、防靜電區(qū)等。在印刷過程中，柔性塑料襯底被支撐在R2R放卷區(qū)和收卷區(qū)并做協(xié)調(diào)運(yùn)動，從而實(shí)現(xiàn)塑料襯底的定向運(yùn)動。在具體的制備過程中，首先是塑料襯底的清洗過程，一般采用醇類溶劑（乙醇、異丙醇等）多次超聲波處理，并低溫退火處理。然后，印刷模頭（通常是槽模頭）以設(shè)定的速度在襯底上涂抹油墨。為保證印刷質(zhì)量，在R2R印刷中加入電暈處理工藝，這將提高襯底的表面能，從而優(yōu)化油墨的滲透。結(jié)合與油墨成膜條件相匹配的退火工藝，可以得到具有條形圖案的干膜。對于OSCs的模組化條狀定位設(shè)計(jì)，襯底的定位偏差可以通過糾偏區(qū)域?qū)崿F(xiàn)，因此，合理改進(jìn)R2R印刷技術(shù)實(shí)際上可以完成除金屬背電極以外的所有OSCs結(jié)構(gòu)的制備，從而實(shí)現(xiàn)完整的印刷器件流程。由于低溫溶液制備的技術(shù)特點(diǎn)，OSCs的印刷工藝與R2R印刷技術(shù)完美兼容（圖5），對此的進(jìn)一步研究也是實(shí)現(xiàn)有機(jī)器件商業(yè)化的關(guān)鍵。

a 模塊制備的總體程序 [167] b 具有獨(dú)立控制參數(shù)的槽模涂層的概念圖 c 槽模涂層裝備的照片和實(shí)現(xiàn)的帶有ZnO層的高質(zhì)量BHJ薄膜 [170] d 熱槽模具涂層示意圖 e R2R熱槽模具涂層的實(shí)驗(yàn)裝備 f 槽模涂層OSCs的J–V特性[169] g 用于監(jiān)測成膜過程中形態(tài)演變的原位印刷技術(shù)示意圖[171]

Krebs等[62]早期就對R2R印刷制備OSCs作出了代表性的研究工作。他們通過狹縫擠出印刷在ITO/PET襯底上沉積ZnO、P3HT∶PCBM和PEDOT∶PSS油墨，然后通過絲網(wǎng)印刷覆蓋頂部金屬銀電極。通過這種方法，他們制備了一個全印刷的倒置OSCs（具體配置為PET/ITO/ZnO/P3HT∶PCBM/PEDOT∶PSS/Ag），其性能可與實(shí)驗(yàn)室小面積旋轉(zhuǎn)涂器件的PCE相媲美。此外，全印刷器件在潮濕的環(huán)境中表現(xiàn)出優(yōu)異的穩(wěn)定性，這優(yōu)于普通器件，但它很容易被氧氣影響。與旋涂器件類似，R2R印刷技術(shù)中也存在各種優(yōu)化思路和薄膜改善方案。在印刷參數(shù)方面，可以通過調(diào)整卷繞張力、基材移動速度、送墨速度、模頭與襯底間距、槽模頭間距等來實(shí)現(xiàn)均勻成膜和厚度控制。此外，也可以應(yīng)用一些常見的后處理工藝，如溶劑退火、溶劑添加劑、給體/受體配置、溶劑退火和納米級相分離調(diào)節(jié)等，其處理效果比旋涂技術(shù)更顯著。與旋涂工藝相比，R2R印刷參數(shù)的控制比旋涂速度和加速度的確定更簡單，材料損耗也少很多。既能降低生產(chǎn)成本，又能減少環(huán)境污染，這對商業(yè)轉(zhuǎn)型至關(guān)重要。更重要的是，R2R印刷技術(shù)提供了更具體、更精確的變量控制，這對于印刷工藝的標(biāo)準(zhǔn)化很重要，這也是旋涂工藝的最大劣勢。例如，對于旋涂工藝，為了獲得準(zhǔn)確的給體/受體比例，需要10多種不同的給體/受體比例，這需要消耗大約100 mg的聚合物材料和60 min。相比之下，對于R2R印刷，至少需要200種不同的給體/受體比例，但僅需要使用60 mg聚合物材料和35 s。這充分展示了R2R印刷技術(shù)的先進(jìn)性[174]。

狹縫擠出印刷和半月板刮涂在OSCs的光電性能方面也存在明顯的缺陷，特別是FF損耗。印刷有機(jī)器件的測試結(jié)果通常呈現(xiàn)“S”型曲線，這與正常器件的“J”型曲線不同。這種現(xiàn)象可能是由于光敏層或界面處的能級勢壘引起的載流子傳輸或提取的損失造成的。光浸泡處理可以緩解這一問題，它可以逐漸將“S”形曲線轉(zhuǎn)變?yōu)椤癑”形曲線，從而實(shí)現(xiàn)FF的恢復(fù)。不幸的是，這種FF損失會在幾天后再次出現(xiàn)，需要進(jìn)一步重復(fù)光浸泡處理[175]。這一動態(tài)降解過程可能與光電導(dǎo)率的變化、ZnO電子傳輸層中雜質(zhì)的降解或封裝器件中殘留氧氣的影響有關(guān)。光浸泡處理通常會帶來大量的能量損失，增加生產(chǎn)成本，并使有機(jī)器件的生產(chǎn)過程復(fù)雜化。同時，這不適合大面積OSCs的連續(xù)制備，因此需要開發(fā)或?qū)ふ倚录夹g(shù)來解決這一缺陷，這也是R2R印刷有機(jī)器件商業(yè)化生產(chǎn)的最大障礙?？偟膩碚f，雖然R2R印刷有明顯的缺陷，但它仍然是實(shí)現(xiàn)OSCs商業(yè)化生產(chǎn)的最佳技術(shù)。特別是柔性器件，下一階段將圍繞有機(jī)器件中這一技術(shù)的研究和設(shè)備開發(fā)。

a 用PDTTDABT生產(chǎn)R2R的照片以及成品模塊的疊層和在太陽模擬器下測試單個模塊的照片[172] b R2R印刷設(shè)備的照片[15] c OSCs模塊及其作為LED條紋和兒童夾克保暖口袋的能源供給者[173] d R2R涂層的PET–ITO卷軸和樣品條[173]

Krebs等[176]定義了大面積印刷OSCs的完整制備工藝，旨在實(shí)現(xiàn)有機(jī)器件從實(shí)驗(yàn)室的小面積制備到工業(yè)界的大面積生產(chǎn)轉(zhuǎn)移。但在生產(chǎn)成本方面，他們的研究沒有考慮到人工成本、材料消耗以及相關(guān)的水電費(fèi)用。報(bào)告的主要研究內(nèi)容是通過印刷一種新型的透明電極來取代ITO電極，這樣可避免OSCs每,層的圖案化過程?；谶@種通過R2R印刷技術(shù)實(shí)現(xiàn)的無ITO透明電極設(shè)計(jì)，結(jié)合含銅的Kapton箔和鈦金屬背電極，全印刷的有機(jī)器件得到0.061%的低PCE，sc為42.57 mA，oc為0.178 V和填充因子（FF）為25%。雖然這種方法為有機(jī)器件的印刷制備提供了指導(dǎo)和參數(shù)規(guī)范，但由于光電轉(zhuǎn)換效率低，不值得進(jìn)一步研究。Bundgaard等[172]展示了通過空氣中的全溶液處理和狹縫擠出印刷技術(shù)，結(jié)合印刷的金屬網(wǎng)格背電極制備的半透明柔性O(shè)SCs。這進(jìn)一步擴(kuò)大了印刷技術(shù)在連續(xù)大面積制造OSCs中的應(yīng)用潛力。Wei等[177]在ITO/PET襯底上沉積了電子傳輸層和光敏層，制備了2節(jié)或4節(jié)串聯(lián)的OSCs和OSMs。對于單結(jié)電池、雙結(jié)串聯(lián)電池和四結(jié)串聯(lián)電池，有機(jī)器件的光電效率分別達(dá)到5.75%、5.82%和5.18%。在校準(zhǔn)后的太陽模擬器下照射強(qiáng)度為100 mW/cm2的AM 1.5G照明下，四節(jié)串聯(lián)OSCs可正常工作。這些結(jié)果初步證明，目前商業(yè)化的R2R印刷技術(shù)可以實(shí)現(xiàn)全印刷OSCs的制備，這是其他印刷技術(shù)所不具備的優(yōu)勢，因此，進(jìn)一步的印刷探索和設(shè)備升級應(yīng)該是首要任務(wù)。Chen等[15]報(bào)道了一種將狹縫擠出R2R印刷設(shè)備制備的柔性有機(jī)光伏器件升級到模塊規(guī)模（15 cm2）而沒有明顯效率損失的一般方法。首先應(yīng)用涂布/印刷過程中的剪切沖力來調(diào)整富勒烯和非富勒烯受體系統(tǒng)的BHJ活性層的形態(tài)演變，并得到狹縫擠出印刷和旋涂之間剪切沖量的定量轉(zhuǎn)換系數(shù)。基于1.04 cm2通過狹縫擠出印刷的柔性O(shè)SCs的PCE在PTB7-Th∶PC71BM和PBDB-T∶ITIC系統(tǒng)中達(dá)到9.10%和9.77%。對于15 cm2的柔性模塊，其有效效率也達(dá)到了7.58%和8.90%，并具備令人滿意的機(jī)械力學(xué)穩(wěn)定性和制備重現(xiàn)性。

4 結(jié)語

隨著科技的飛速發(fā)展，可穿戴電子設(shè)備逐漸在生活中發(fā)揮著越來越重要的作用，因此，柔性連續(xù)電源器件作為其核心部件之一，其研究具有科學(xué)和實(shí)際應(yīng)用意義，可應(yīng)用于電動汽車、便攜式電子設(shè)備和物聯(lián)網(wǎng)領(lǐng)域。具有優(yōu)良光電轉(zhuǎn)換性能和環(huán)境穩(wěn)定性的大面積OSCs有望適應(yīng)未來民用光伏器件的實(shí)際應(yīng)用，特別是柔性O(shè)SCs在可穿戴電子領(lǐng)域具有巨大潛力。遺憾的是，盡管在剛性和柔性襯底上，單結(jié)OSCs的最大PCE已經(jīng)超過19%和16%，但現(xiàn)有的制備技術(shù)（旋涂等）、功能層材料和器件配置都不適合大面積OSMs的工業(yè)制備，因此，即使在選擇性能最好的給體/受體材料體系時，印刷技術(shù)的合理選擇、大面積印刷工藝的巨大性能損失仍然是限制OSCs商業(yè)化的瓶頸。

在此，文中總結(jié)了柔性O(shè)SCs各功能材料的可行性選擇，各種印刷技術(shù)的優(yōu)勢和挑戰(zhàn)，以及OSMs性能的優(yōu)化思路。文中旨在為讀者提供與先進(jìn)的印刷制備OSCs相關(guān)的全面見解和最新進(jìn)展，通過分析現(xiàn)階段的技術(shù)瓶頸和大面化制備OSCs過程中的效率損失，以獲得高性能、可印刷的大面積光伏組件。希望通過這篇綜述，為推動下一代柔性光伏清潔能源的商業(yè)化提供一站式參考，并突出低溫溶液法印刷有機(jī)光伏組件的技術(shù)優(yōu)勢。同時也相信，只要合理設(shè)計(jì)光伏材料、設(shè)計(jì)合理的模組化OSCs結(jié)構(gòu)和合適的印刷技術(shù)選擇，就能實(shí)現(xiàn)低效率損失的柔性有機(jī)光伏器件的連續(xù)印刷制備，未來有機(jī)太陽電池的商業(yè)化制造也將近在咫尺。

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Large-area Flexible Organic Solar Cells: Modular Design and Printing Technologies

SHI Lin-feng1, YUAN Hao1, MENG Xiang-chuan1,2, HU Xiao-tian1,2, CHEN Yi-wang1,2,3

(1. Peking University Yangtze Delta Institute of Optoelectronics, Jiangsu Nantong 226010, China; 2. College of Chemistry/Institute of Polymers and Energy Chemistry (IPEC), Nanchang University, Nanchang 330031, China; 3. Institute of Advanced Scientific Research (iASR)/Key Lab of Fluorine and Silicon for Energy Materials and Chemistry of Ministry of Education, Jiangxi Normal University, Nanchang 330022, China)

The work aims to provide investigators with comprehensive insights and recent advances related to OSCs manufacturing technology, analyze existing technical bottlenecks and unsolved scale efficiency losses to obtain scalable and printable large-area photovoltaic modules. This review introduced the selection of functional layer materials, the current status of printing process research and large-scale efficiency loss, and focused on the technical challenges in printing and preparation of flexible and high-efficiency large-area organic photovoltaic devices. This will promote the integrated application of printable organic semiconductor materials in next-generation clean energy, and attract widespread attention in application to wearable electronics, building-integrated photovoltaics, the Internet of Things, etc.

organic photovoltaic, modular design, flexible device, printing technology

TS801.4

A

1001-3563(2022)19-0011-16

10.19554/j.cnki.1001-3563.2022.19.002

2022–07–12

國家自然科學(xué)基金（51833004，22005131，52173169，52222312）

施淋楓（1991—），女，中級，主要研究方向?yàn)橛∷⒐怆娖骷?/p>

胡笑添（1990—），男，博士，研究員，主要研究方向?yàn)橛∷⒐怆娖骷?/p>

責(zé)任編輯：曾鈺嬋