실내 페로브스카이트 태양전지를 위한 진공 열 어닐링을 통한 강력한 페로브스카이트 형성

Oct 14, 2023

Scientific Reports 13권, 기사 번호: 10933(2023) 이 기사 인용

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페로브스카이트 재료는 차세대 태양광 장치를 위한 매력적인 후보입니다. 전하 캐리어 수명이 긴 금속 할로겐화물 페로브스카이트는 저조도 수확에 적합한 후보로 알려져 있습니다. 실내 조명의 방사 조도 스펙트럼을 일치시키기 위해 최적의 밴드 갭( 예) \(\sim\)1.80 eV. 실내 조건에서 광자 플럭스가 낮을 경우 최소한의 재결합이 매우 바람직합니다. 이러한 목표를 달성하기 위해 우리는 처음으로 반용매 증착과 진공 열 어닐링, 즉 VTA의 이중 사용을 결합하여 고품질 페로브스카이트 필름을 제조했습니다. VTA는 엑시톤 손실의 주요 원인인 표면 및 결정립계의 트랩 상태를 억제하면서 콤팩트하고 조밀하며 단단한 형태를 구현합니다. 저가형 탄소 전극 아키텍처를 사용하여 VTA 장치는 27.7 ± 2.7%의 평균 전력 변환 효율(PCE)을 나타냈으며 피크 PCE는 32.0%(Shockley-Queisser 한계는 50~60%) 및 평균 개방 회로 전압(Voc)은 0.93 ± 0.02 V, 피크 Voc는 0.96 V로, 가열 전 제어 및 진공 처리보다 훨씬 높습니다.

Energy demand has been dramatically increasing owing to population explosion and industrial expansion. Metal-halide perovskite-based materials are fascinating candidates for the next-generation solar devices. Because of exceptional light to electricity conversion characteristic and rapid increase of PCE over time to more than 25%, they are extremely promising for future commercial applications with PCE rivaling those of silicon solar cells1,2. Furthermore, perovskite solar cells (PSCs) have good optoelectronic properties such as high absorption over the visible spectrum3, low exciton binding energies4, low non-radiative recombination rates5, long charge carrier diffusion lengths in the \(\mu\)m range, and tunable energy band gaps (Eg) from 1.47 to more than 3.06 eV6,7. Interestingly, fabrication processes of PSCs are facile and economical with low consumption of energy due to high solubility at temperatures less than 100 °C8,9. Perovskite materials can be deposited by using several approaches, such as spin coating, vapor assisted solution deposition, thermal vapor deposition, inkjet printing, slot-die coating, and spray coating10,11,12,13. However, spin-coating deposition is a simple method for laboratory scale perovskite fabrication. One-step spin coating is a technique where precursor solution is directly spin–coated onto substrates14,15. Using antisolvent in one–step deposition, repeated cation doping, or adding some additives could be used to obtain large grain size, along with uniform and dense perovskite films10,16. Interestingly, Eg of perovskite-based materials with ABX3 structure can be tuned by substitution engineering at any site (A, B, and/or X), which is an advantage of perovskite technology, enabling several applications such as light emitting diodes (LEDs), photodetectors (PDs), and solar cells for both outdoor and indoor conditions. Up until now, researchers have paid a lot of attention to photovoltaics for low light that can be applied to portable electronics and wireless telecommunication technologies because of the rise of Internet of Things (IoTs)17,18,19. Perovskite–based materials are widely tunable in terms of energy band gaps, allowing a variety of Eg values each for an optimal performance under a specific light condition20,21. As indoor light sources provide different spectrum outputs compared to those of sunlight; according to computational calculation21,22, the well-fit energy band gap for indoor applications ranges from 1.8 to 1.9 eV, which can be achieved by partial substitution of A-site with cesium (Cs), methylammonium (MA), and/or formamidinium (FA) and/or X-site via iodine (I), bromine (Br), and/or chlorine (Cl)22,23,24,25,26. Cheng, R. et al. reported energy band gap tuning by the introduction of Br and Cl into pristine MAPbI3 perovskite. The Eg can be enlarged from 1.61 to 1.80 eV (MAPbI2−xBrClx). Moreover, the addition of chlorine reduces trap-state density, halide migration, and non-radiative recombination while improving crystallization, resulting in high open circuit voltage (Voc) of 1.028 V and PCE of 36.2% under 1000 lux fluorescent light21. Cheng, R. et al. demonstrated that perovskite solar cell performance was improved, particularly for indoor light applications by chlorine additive. The chlorine doping contributes to higher extraction capability at the perovskite/hole transport layer interface, which is attributed to lower defects19. With proper addition of Br, the grain sizes of perovskite were enlarged, suppressing non-radiative recombination. Moreover, the stability was improved by the formation of a pseudo-cubic phase and PCE of 34.5% was realized 34 %) of perovskite photovoltaics with controlled bromine doping”. Nano Energy 75, 104984. https://doi.org/10.1016/j.nanoen.2020.104984 (2020)." href="/articles/s41598-023-37155-4#ref-CR27" id="ref-link-section-d5183487e721"27. Apart from the perovskite absorber layer, electron transport layer (ETL) also plays important roles. Ann, M. H. et al. reported that compact TiO2 (c-TiO2) layer was more efficient for indoor light applications than mesoporous TiO2 (m-TiO2) layer owing to the high density of interfacial traps from using m-TiO2, although m-TiO2 was better for one sun condition28. Dagar, J. et al. also reported tin oxide (SnO2) as the electron transport layer for perovskite solar cell tested under indoor illumination, showing PCE of 21.3% at 400 lux29. From previous studies, the trap states at the interfaces and/or the grain boundaries are the main sources of non-radiative recombination22,23,28. Especially for low light applications, trap-state density is of great importance as there are less photo-generated charges under indoor light environment. To circumvent this problem under one sun, researchers have paid attention to the application of vacuum treatment to boost nucleation during crystallization and remove residual solvents without using antisolvent30,31,32. Li, X. et al. applied vacuum treatment to fabricate FA0.81MA0.15PbI2.51Br0.45 in DMSO-GBL solvent system and put the wet film under a vacuum environment for a few seconds to promote DMSO-PbI1.7Br0.3-(FAI)0.85(MABr)0.1 intermediate phase by eliminating solvent. The intermediate phase could delay crystal growth, leading to larger grain size and a high PCE of 20.5% under one sun30. In another study, low band gap FA0.8MA0.2Sn0.5Pb0.5I3 was deposited by applying vacuum-assisted growth control (VAGC) instead of antisolvent technique; the wet spin-coated films were placed under vacuum at 10 Pa for 10 s and further annealed under N2 atmosphere, resulting in smooth surfaces, no pin holes, large columnar grain orientations, fast transportation of charge carriers, and improved charge-carrier lifetime32. Zhang, J. et al. fabricated quasi-2D PEA2MAn-1PbnI3n+1 film by spin coating and vacuum treatment of the wet film to create uniform dispersion of different-n-value nanoplates to boost nucleations and limit the grain sizes by fast evaporation of residual solvents. The vacuum-treated films exhibited high fill factor (FF) of 82.4% and PCE of 18.04%31. Bi, D. et al. reported that perovskite solution (FA0.9Cs0.1PbI3) was added with molecular modulators (S, N, and SN) and fabricated by the one-step deposition method and then applied with a short vacuum treatment after spin coating to remove N, N-dimethylformamide (DMF) without using antisolvent to encourage fast crystallization of the intermediates. As a result, they achieved a PCE of over 20% with an active area of 1 cm233. Vacuum treatment was also applied to two-step deposition during the perovskite formation when MAI was dropped onto a PbI2 film, resulting in rapid solvent removal and a supersaturated state where a tremendous amount of nuclei are formed and simultaneously grown under the competitive pressure from neighbor nuclei; as a result, compact and smooth perovskite films with high hardness and thermal stability were produced34. Moreover, vacuum process can be applied during thermal annealing. Xie, F. X. et al. reported the CH3NH3PbI3 film fabricated by conducting vacuum treatment during thermal annealing to eliminate CH3NH3Cl (MACl), which is an unwanted byproduct of the reaction: 3CH3NH3I + PbCl2 \(\to\) CH3NH3PbI3 + 2CH3NH3Cl, yielding a high PCE of 14.5%35. Feng, J. et al. reported Cs0.15FA0.85PbI3 films fabricated under an all vacuum process. The PbI2, FAI, and CsI were separately evaporated layer-by-layer; all precursor layers react to form complete perovskite by annealing under vacuum environment. As a result, they obtained PCE of 21.32%36./p>

The XRD patterns of perovskite films fabricated with and without VTA are illustrated in Fig. 2A. We found full transformation into perovskite thin films since PbI2 and hexagonal non-perovskite phase (δ-phase) peak could not be detected36, 50%. RSC Adv. 9(18), 10148–10154. https://doi.org/10.1039/c9ra01625b (2019)." href="/articles/s41598-023-37155-4#ref-CR39" id="ref-link-section-d5183487e1204"39. The XRD peak of our samples located at 14.5° corresponds to the crystallographic plane of (100), which is cubic phase40. The peak positions of perovskite are shifted to higher 2\(\uptheta\) degrees compared with our reference, which is around 14.0°40. According to Bragg’s law,/p>

34 %) of perovskite photovoltaics with controlled bromine doping”. Nano Energy 75, 104984. https://doi.org/10.1016/j.nanoen.2020.104984 (2020)./p> 50%. RSC Adv. 9(18), 10148–10154. https://doi.org/10.1039/c9ra01625b (2019)./p>