Nanoscale, 2019, 11,11173-11182 DOI: 10.1039/C9NR01645G, Paper
Hung Q. Pham, Russell J. Holmes, Eray S. Aydil, Laura Gagliardi Two indium-based double perovskites, Cs2InCuCl6 and (CH3NH3)2InCuCl6, were proposed as promising materials for photovoltaic and optoelectronic applications with a suitable band gap and exceptional optical and electrical properties. The content of this RSS Feed (c) The Royal Society of Chemistry
J. Mater. Chem. C, 2019, 7,7548-7553 DOI: 10.1039/C9TC01763A, Paper
Ying Su, Qinghui Zeng, Xuejiao Chen, Weiguang Ye, Lushuang She, Ximing Gao, Zhongyuan Ren, Xiaomeng Li The structure transformation from CsPbBr3 to Cs4PbBr6 perovskite nanocrystals induced fluorescence enhancement was detected and applied in the LED devices. The content of this RSS Feed (c) The Royal Society of Chemistry
by Hang Zhao,
Jia Xu,
Shijie Zhou,
Zhenzhen Li,
Bing Zhang,
Xin Xia,
Xiaolong Liu,
Songyuan Dai,
Jianxi Yao
Nondoped and Ca2+‐doped γ ‐CsPbI3 films are prepared at low temperature (60 °C). The theoretical simulation and experimental results testify that adding Ca2+ can lower the total cohesive energy of γ‐CsPbI3 and yield a more stable γ‐CsPbI3 film. The Ca2+‐doped γ‐CsPbI3 perovskite solar cells achieve a hysteresis‐free J–V curve and a maximum power conversion efficiency of 9.20%.
Abstract
Inorganic cubic CsPbI3 perovskite (α‐CsPbI3) has been widely explored for perovskite solar cells (PSCs) due to its thermal stability and suitable bandgap of 1.73 eV. However, α‐CsPbI3 usually requires high synthesis temperatures (>320 °C). Additionally, it usually undergoes phase transition to the nonperovskite structure phase (β‐CsPbI3), which results in poor photoelectric performance in devices. In this study, it is first found that the tortuous 3D CsPbI3 phase (γ‐CsPbI3) can be prepared and used for PSCs by solution process without any additive at low temperature (60 °C). The γ‐CsPbI3 exhibits suitable bandgap of 1.75 eV and favorable photoelectric properties. However, γ‐CsPbI3 is a metastable phase and easily transforms into β‐CsPbI3 in ambient moisture. In order to improve the stability of γ‐CsPbI3, calcium ions (Ca2+) with a relatively small radius of 100 pm are used to partially substitute lead ions (119 pm). This research proves that Ca2+ can effectively improve the stability of the γ‐CsPbI3 at room temperature. By optimizing the doping concentration of Ca2+ (CsPb1−xCaxI3, x is from 0% to 2%), the Ca2+‐doped γ‐CsPbI3 PSCs achieve a hysteresis‐free J–V curve and a maximum power conversion efficiency (PCE) of 9.20%.
J. Mater. Chem. C, 2019, 7,6956-6963 DOI: 10.1039/C9TC01741K, Paper
Chongyang Xu, Zhihai Liu, Eun-Cheol Lee A mixture of C60/C70 can improve the solubility and maintain the original electron-transport property at the same time. The content of this RSS Feed (c) The Royal Society of Chemistry
by Yuliar Firdaus,
Vincent M. Le Corre,
Jafar I. Khan,
Zhipeng Kan,
Frédéric Laquai,
Pierre M. Beaujuge,
Thomas D. Anthopoulos
The efficiency limits in non‐fullerene organic solar cells are examined using a numerical simulator. Power conversion efficiency (PCE) of over 18% using recently reported carrier mobility values and voltage losses, are predicted. Increasing the mobility to >10−3 cm2 V−1 s−1 and decreasing the recombination constant to <10−12 cm3 s−1 is shown to yield a single‐junction and 2T‐tandem cell with PCEs of >20% and >25%, respectively.
Abstract
The reported power conversion efficiencies (PCEs) of nonfullerene acceptor (NFA) based organic photovoltaics (OPVs) now exceed 14% and 17% for single‐junction and two‐terminal tandem cells, respectively. However, increasing the PCE further requires an improved understanding of the factors limiting the device efficiency. Here, the efficiency limits of single‐junction and two‐terminal tandem NFA‐based OPV cells are examined with the aid of a numerical device simulator that takes into account the optical properties of the active material(s), charge recombination effects, and the hole and electron mobilities in the active layer of the device. The simulations reveal that single‐junction NFA OPVs can potentially reach PCE values in excess of 18% with mobility values readily achievable in existing material systems. Furthermore, it is found that balanced electron and hole mobilities of >10−3 cm2 V−1 s−1 in combination with low nongeminate recombination rate constants of 10−12 cm3 s−1 could lead to PCE values in excess of 20% and 25% for single‐junction and two‐terminal tandem OPV cells, respectively. This analysis provides the first tangible description of the practical performance targets and useful design rules for single‐junction and tandem OPVs based on NFA materials, emphasizing the need for developing new material systems that combine these desired characteristics.
by Chun Ma,
Changxu Liu,
Jianfeng Huang,
Yuhui Ma,
Zhixiong Liu,
Lain-Jong Li,
Thomas D. Anthopoulos,
Yu Han,
Andrea Fratalocchi,
Tom Wu
Various strategies related to light management and photocarrier collection are developed to enhance perovskite solar cell performance. The exploration of novel plasmonic nanostructures with predesigned size and shape is needed in the field. Herein, a bioinspired nanostructure of Au nanorod–nanoparticle dimers with structural darkness is used to enhance the light harvesting and performance of perovskite solar cells.
Hybrid perovskites have recently attracted enormous attention for photovoltaic applications, and various strategies related to light management and photocarrier collection are developed to enhance their performance. As an effective route toward near‐field light enhancement, metal nanostructures with subwavelength dimensions can couple incident photons with conduction electrons, giving rise to localized surface plasmon resonances. However, efficiency enhancements through plasmonic routes are limited to the short wavelength range corresponding to metal extinction wavelength. Thus, the exploration of novel plasmonic nanostructures with predesigned sizes and shapes is needed to advance this field. Herein, for the first time, a bioinspired nanostructure of Au nanorod–nanoparticle dimers with structural darkness is exploited to enhance the light harvesting and performance of perovskite solar cells. Differing from conventional metallic nanoparticles, biometric nanoparticles introduce geometric singularity to the system, providing a broadband response for energy harvesting. By embedding the core–shell gold dimers in the perovskite solar cells, a notable enhancement of broadband light absorption is observed, and sequentially, the efficiency of perovskite solar cells increases by 16%.
J. Mater. Chem. A, 2019, 7,13215-13224 DOI: 10.1039/C9TA02209K, Paper
Philipp Maisch, Lena M. Eisenhofer, Kai Cheong Tam, Andreas Distler, Monika M. Voigt, Christoph J. Brabec, Hans-Joachim Egelhaaf A novel strategy to overcome wetting problems is applied to manufacture inverted structure P3HT:O-IDTBR solar cells with 5% efficiency. The content of this RSS Feed (c) The Royal Society of Chemistry
J. Mater. Chem. A, 2019, 7,13256-13264 DOI: 10.1039/C9TA03351C, Paper
Xiaobing Wang, Jihuai Wu, Yuqian Yang, Xuping Liu, Qiyao Guo, Zeyu Song, Guodong Li, Zhang Lan, Miaoliang Huang Perovskite solar cells with vanadic oxide doping achieve a power conversion efficiency of 20.5%. The content of this RSS Feed (c) The Royal Society of Chemistry
Author(s): Yuanhang Cheng, Menglin Li, Xixia Liu, Sin Hang Cheung, Hrisheekesh Thachoth Chandran, Ho-Wa Li, Xiuwen Xu, Yue-Min Xie, Shu Kong So, Hin-Lap Yip, Sai-Wing Tsang
Abstract
Despite the success of solution processed nickel oxide (s-NiOx) as the hole transporting layer (HTL) in organic solar cells, applying s-NiOx in perovskite solar cells (PVSCs) is not that straight forward. The reported power conversion efficiencies (PCEs) of the s-NiOx based PVSCs span a wide range from 8% to over 20% even with a similar recipe. Here, we report that one of the causes for the performance discrepancy might be the large surface dipole on the s-NiOx surface. We find that the perovskite deposited on the as-prepared sol-gel derived s-NiOx has large number of defects at the s-NiOx/perovskite interface. Based on the in-depth mechanism study with various spectroscopy techniques, we propose that the strong surface dipole of the s-NiOx composite film induces adhesion of perovskite precursor ions on the surface of s-NiOx during the perovskite film formation and creates defects in the perovskite crystals at the interface. Such interfacial dipole-ion attachment has been demonstrated can be dissociated by ultraviolet (UV) light soaking experiment. The high energy of the UV light helps to dissociate the physical dipole-ion attachment and mobilize the ions to accommodate the perovskite defect sites. The defect density of the perovskite film on s-NiOx has been significantly reduced by an amount of 4.1 × 1017 cm−3 after the UV light soaking as evidenced by photothermal deflection spectroscopy (PDS) measurement. By treating the s-NiOx surface with a dipolar molecule n-Butylamine, the surface dipole of the s-NiOx film is efficiently reduced and it significantly reduces the defect density in the perovskite film. As a result, the PVSCs based on the n-Butylamine treated s-NiOx layer have achieved a dramatical enhancement in PCE to 18.9% with decent stability at the maximum power point tracking. It is believed that this work provides insight and strategy to develop highly reproducible PVSCs with solution derived metal oxide as interlayers.
by Cho Fai Jonathan Lau, Meng Zhang, Xiaofan Deng, Jianghui Zheng, Jueming Bing, Qingshan Ma, Jincheol Kim, Long Hu, Martin A. Green, Shujuan Huang, Anita Ho-Baillie
by Fei Zheng,
Weijian Chen,
Tongle Bu,
Kenneth P. Ghiggino,
Fuzhi Huang,
Yibing Cheng,
Patrick Tapping,
Tak W. Kee,
Baohua Jia,
Xiaoming Wen
The passivation effect of K+ doping in mixed‐cation mixed‐halide perovskite is triggered by light illumination to form stable KBr‐like compounds and reduce the interface trapping defect density to facilitate a high‐efficiency and hysteresis‐free perovskite solar cell.
Abstract
Potassium (K+) doping has been recently discovered as an effective route to suppress hysteresis and improve the performance stability of perovskite solar cells. However, the mechanism of these K+ doping effects is still under debate, and rationalization of the improved performance in these perovskites is needed. Herein, the photoluminescence (PL) properties and device performance of mixed‐cation mixed‐halide perovskite are dynamically monitored with and without K+ doping under bias light illumination via a confocal fluorescence microscope, together with ultrafast transient absorption as well as time‐dependent and time‐resolved PL measurements. It is demonstrated that illumination is essential to trigger the passivation effect of K+ by forming KBr‐like compounds, leading to the elimination of interface trapping defects and suppression of mobile ion migration, thus resulting in improved power conversion efficiency and negligible current–voltage hysteresis of solar cells. This work provides novel insight into the hysteresis suppression upon K+ doping and highlights the significance of light illumination when using this protocol.
by Zhili Ye,
Junshuai Zhou,
Jie Hou,
Fei Deng,
Yan-Zhen Zheng,
Xia Tao
Pb(SCN)2 functions at the grain boundaries and pinholes to in situ polish the perovskite film surface. A 425 nm‐thick CsPbI2Br film with high crystalline, smooth, and uniform surface morphology is obtained, with an efficiency of 10.44% for a low cost and stable carbon‐based perovskite solar cell processed under low‐temperature (150 °C).
Improvement in stability and an economical processing technique are the main aspects of the commercialization of perovskite solar cells (PSCs). In this study, a 425 nm‐thick CsPbI2Br film with a high crystalline, smooth, and uniform surface morphology is obtained by Pb(SCN)2 passivating the grain boundaries under low temperature (150 °C). The results of a series of electrochemical analyses, including space‐charge‐limited‐current (SCLC), open‐circuit voltage decay (OCVD), electrical impedance spectroscopy (EIS), intensity‐modulated photocurrent spectroscopy (IMPS), and intensity‐modulated photovoltage spectroscopy (IMVS), demonstrate that the trap density of the CsPbI2Br film is greatly reduced with Pb(SCN)2, which effectively inhibits the interface recombination and promotes charge transport in CsPbI2Br PSC. Efficiencies of 12.22% and 10.44% are achieved for low‐temperature‐processed CsPbI2Br planar‐architecture PSCs with ITO/SnO2/CsPbI2Br/ poly(3‐hexylthiophene) (P3HT)/Ag and ITO/SnO2/CsPbI2Br/carbon, respectively. This low‐cost, high‐efficiency carbon‐based inorganic PSC shows potential industrial application, especially for tandem solar cells.
by Qiaoyun Chen,
Ligang Yuan,
Ruomeng Duan,
Peng Huang,
Jianfei Fu,
Hui Ma,
Xiaocheng Wang,
Yi Zhou,
Bo Song
A betaine‐based zwitterionic polymer poly sulfobetaine methacrylate (PSBMA) is employed as interfacial material in p‐i‐n perovskite solar cells. Through improving the interfacial affinity and regulating the energy level at the anode and cathode, respectively, the power conversion efficiency as well as storage stability of the devices greatly improve. In addition, PSBMA also shows advantages in large active area devices.
To improve the performance of perovskite solar cells (Pero‐SCs), a betaine‐based zwitterionic polymer poly(sulfobetaine methacrylate) (denoted by PSBMA) is employed as interlayers at both the anode and cathode in p‐i‐n Pero‐SCs. 1) At the anode side, PSBMA acts as a glue to stitch the two interfacially unfavorable materials: perovskite and poly(bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine), by which the quality of perovskite films as well as the corresponding device performance greatly improve. 2) At the cathode side, PSBMA smoothes the energy levels between PC61BM and Al, and thus facilitates the electron injection efficiency. The power conversion efficiency (PCE) is promoted from 17.31% to 19.16% after PSBMA is introduced as both anode and cathode sides of the p‐i‐n Pero‐SCs. More importantly, PSBMA also shows great potential for large active area (1 cm × 1 cm) Pero‐SCs, and a PCE as high as 15.7% is achieved.
Author(s): Zhi Fang, Minghui Shang, Xinmei Hou, Yapeng Zheng, Zhentao Du, Zuobao Yang, Kuo-Chih Chou, Weiyou Yang, Zhong Lin Wang, Ya Yang
Abstract
A relatively wide bandgap and intrinsically phase instability of α-CsPbI3 perovskites (PVSKs) greatly hinder their potential applications in solar cells. One of the popular solutions is based on high-concentration doping, which however encounters big difficulty in the balance between phase stability and optical performance. Here, we report the advance on bandgap alignment of CsPbI3 through B-site (Pb2+ cation) minor doping engineering employing density functional theory (DFT). It is discovered that the bandgaps could be finely aligned by minor doping of Si2+, Sn2+ and Ge2+, which is caused by the downshift of conduction band minimum contributed by B-p orbital level within CsPb1-xBxI3 PVSKs, and thus offer shrunken gaps and enlarged imaginary part of dielectric function for enhanced photo absorption. Furthermore, the minor doping of Sn2+ could not only bring a suitable tolerance factor for CsPbI3 with a slighter lattice distortion, but also increase the charge density of Pb2+ to enhance the interaction between Pb2+ and I−, which consequently improve their structure stability.
Graphical abstract
We reported the advance on bandgap alignment of α-CsPbI3 perovskites (PVSKs) through B-site minor doping engineering with synergistically enhanced stability and optical property, which was predicted by density functional theory calculation. The present work establishes the rule that the bandgaps of α-CsPbI3 PVSKs decrease with the sequential change of dopants from Ge, to Sn and then to Si at a fixed doping level, and reduce with the raise of doping concentrations for a given dopant, suggesting the bandgap engineering of PVSKs via B-site minor doping strategy. Furthermore, it is discovered that minor doping of Sn2+ with an optimal concentration 2.8 at.% could not only bring a suitable tolerance factor for CsPbI3 PVSKs with a slighter lattice distortion, but also increase the charge density of Pb2+ to enhance the interaction between Pb2+ and I−, which consequently improve their global stability. Current work might direct and advance the exploration of novel PVSKs with totally improved performance, which could inspire their future applications in efficient solar cell.
by Shafket Rasool, Nasir Khan, Muhammad Jahankhan, Da Hun Kim, Thuy Thi Ho, Ly Thi Do, Chang Eun Song, Hang Ken Lee, Sang Kyu Lee, Jong-Cheol Lee, Won-Wook So, Sang-Jin Moon, Won Suk Shin
by Lijun Hu,
Jiehao Fu,
Ke Yang,
Zhuang Xiong,
Ming Wang,
Bo Yang,
Xinhua Wang,
Xiaosheng Tang,
Zhigang Zang,
Meng Li,
Jun Li,
Kuan Sun
An oxidized poly(3,4‐ethylenedioxythiphene):poly(styrenesulfonate) (PEDOT:PSS) monolayer is constructed to demonstrate the in‐plane movement of charge carriers in the charge transfer layer, which possibly leads to severe charge recombination at the interfaces. Consequently, a perovskite solar cell fabricated on the oxidized PEDOT:PSS monolayer yields a power conversion efficiency of 18.8% with a high fill factor of 82%.
Charge extraction at the active layer‐electrode interfaces is critical in obtaining highly efficient planar perovskite solar cells (PSCs). It is commonly achieved by enhancing the charge carrier mobility of the charge transfer layer (CTL) that possesses a desirable energy level. Nevertheless, the in‐plane movement of charge carriers in the CTL possibly leads to severe charge recombination in the presence of defects at the interfaces. To verify this overlooked possibility, herein, an oxidized monolayer of poly(3,4‐ethylenedioxythiphene):poly(styrenesulfonate) (PEDOT:PSS) hole transfer layer (HTL) is constructed by water rinsing followed by H2O2 oxidation. The oxidized PEDOT:PSS monolayer ensures a high charge transfer ability from perovskite to electrode, but at the same time limits in‐plane charge transport. An inverted planar PSC fabricated on the oxidized PEDOT:PSS monolayer yields a power conversion efficiency (PCE) of 18.8%, higher than 17.0% of the control device based on a pristine PEDOT:PSS monolayer. The main contribution comes from the fill factor (FF), which is as high as 82%. Characterizations indicate that the conjugation length of PEDOT chains is decreased after H2O2 oxidation, which lowers the conductivity of PEDOT:PSS HTL in the in‐plane direction. This study suggests that the charge recombination at the electrode interfaces due to in‐plane charge transport in the CTLs is not to be neglected.
Author(s): Francesco Lamberti, Teresa Gatti, Enrico Cescon, Roberto Sorrentino, Antonio Rizzo, Enzo Menna, Gaudenzio Meneghesso, Moreno Meneghetti, Annamaria Petrozza, Lorenzo Franco
The Bigger Picture
The development of solid-state hole-transporting materials (HTMs) dates back to the first reports on solid-state dye-sensitized solar cells in 1998, which provided solar cell efficiencies around 1%. The need for these components has then steadily grown with the advent in 2009 of perovskite-based photovoltaics, which cannot sustain any liquid electrolyte. Spiro-OMeTAD molecules have been for many years the material of choice for this application. When doped with LiTFSI salts and tert-butylpyridine, the resulting mixture can efficiently extract photogenerated holes in the perovskite absorber and transport them to the collecting electrode. This benchmark for hole transport in third-generation hybrid photovoltaics suffers from intrinsic limitations, which have been studied widely over the years. A detailed molecular-level understanding of the processes involved in Spiro-OMeTAD-based HTM degradation is a key requirement for the future development of new stable and efficient substitutes for this task.
Summary
Spiro-OMeTAD is the most-employed molecular hole-transporting material (HTM) in n-i-p perovskite solar cells (PSCs). Ease of processing from solution and good filmability on top of the perovskite photo-active layer are characteristics that make this HTM outstanding and incomparable for the role. However, chemical doping with both tert-butylpyridine (tBP) and lithium bis(trifluoromethylsulfonyl)-imide (LiTFSI), coupled with further oxidation steps, is required in order to achieve high hole mobility and conductivity. Previous investigations have revealed that tBP is fundamental for addressing the best morphology in the hole-transporting layer during processing. Here, we provide spectroscopic evidence of the detrimental impact on long-term conservation of Spiro-OMeTAD structural and electrical properties when tBP is used as an additive. These aspects are crucial for the future design and understanding of new molecular HTMs for PSCs.
by Licheng Tan,
Yilin Wang,
Jingwen Zhang,
Shuqin Xiao,
Huanyu Zhou,
Yaowen Li,
Yiwang Chen,
Yongfang Li
A low temperature–processed metal oxide with excellent mechanical properties and thickness‐insensitivity is exploited as an electron transporting layer for high‐efficiency robust flexible polymer solar cells (PSCs). A record efficiency of 11.5% is achieved for the flexible PSCs, and over 91% of initial efficiency is well maintained after 1500 bending cycles.
Abstract
Landmark power conversion efficiency (PCE) over 14% has been accomplished for single‐junction polymer solar cells (PSCs). However, the inevitable fracture of inorganic transporting layers and deficient interlayer adhesion are critical challenges to achieving the goal of flexible PSCs. Here, a bendable and thickness‐insensitive Al‐doped ZnO (AZO) modified by polydopamine (PDA) has emerged as a promising electron transporting layer (ETL) in PSCs. It has special ductility and adhesion to the active layer for improving the mechanical durability of the device. Nonfullerenes PSCs based on PBDB‐T‐2F:IT‐4F with AZO:1.5% PDA (80 nm) ETL yield the best PCE of 12.7%. More importantly, a prominent PCE, approaching 11.5%, is reached for the fully flexible device based on Ag‐mesh flexible electrode, and the device retains >91% of its initial PCE after bending for 1500 cycles. Such thickness insensitivity, mechanical durability, and interfacial adhesion properties for the inorganic ETLs are desired for the development of flexible and wearable PSCs with reliable photovoltaic performance and large‐area roll‐to‐roll printing manufacture.
Xixia Liu, Yuanhang Cheng, Chao Liu, Tianxiang Zhang, Nengduo Zhang, Siwen Zhang, Jingshen Chen, Qinghua Xu, Jianyong Ouyang, Hao Gong The content of this RSS Feed (c) The Royal Society of Chemistry
by Jafar I. Khan,
Raja S. Ashraf,
Maha A. Alamoudi,
Mohammed N. Nabi,
Hamza N. Mohammed,
Andrew Wadsworth,
Yuliar Firdaus,
Weimin Zhang,
Thomas D. Anthopoulos,
Iain McCulloch,
Frédéric Laquai
The power conversion efficiency of poly(3‐hexylthiophene) P3HT:O‐IDTBR bulk heterojunction solar cells peaks at intermediate (34 kDa) polymer molecular weights (MWs). Combined transient absorption and time‐delayed collection field experiments demonstrate that charges are generated more efficiently at intermediate P3HT MWs compared with high and low MWs.
Large‐scale production of organic solar modules requires low‐cost and reliable materials with reproducible batch‐to‐batch properties. In case of polymers, their (photo)physical properties depend strongly on the polymers’ molecular weight (MW). Herein, the impact of the MW of the donor polymer poly(3‐hexylthiophene) (P3HT) on the photophysics is studied in blends with a recently developed rhodanine‐endcapped indacenodithiophene nonfullerene acceptor (IDTBR), a bulk heterojunction (BHJ) system that potentially fulfills the aforementioned criteria for large‐scale production. It is found that the power conversion efficiency (PCE) increases when the weight‐average MW is increased from 17 kDa (PCE: 4.0%) to 34 kDa (PCE: 6.6%), whereas a further increase in MW leads to a reduced PCE of 4.4%. It is demonstrated that the charge generation efficiency, as estimated from time‐delayed collection field experiments, varies with the P3HT MW and is the reason for the differences in photocurrent and device performance. These findings provide insight into the fundamental photophysical reasons of the MW dependence of the PCE, which is taken into account when using polymer‐based nonfullerene acceptor blends in solar cell devices and modules.
J. Mater. Chem. C, 2019, 7,6391-6397 DOI: 10.1039/C9TC01058K, Paper
Ke-Hao Hu, Zhao-Kui Wang, Li Meng, Kai-Li Wang, Yue Zhang, Liang-Sheng Liao The BHJ composed of PTB7 and ITIC was penetrated into the CH3NH3PbI3 layer via anti-solvent engineering. The content of this RSS Feed (c) The Royal Society of Chemistry
by Zhenghui Luo,
Fei Wu,
Teng Zhang,
Xuan Zeng,
Yiqun Xiao,
Tao Liu,
Cheng Zhong,
Xinhui Lu,
Linna Zhu,
Shihe Yang,
Chuluo Yang
The combination of perylene diimide and fullerene results in a new hybrid as electron transporting material (ETM) in inverted perovskite solar cells. This hybrid ETM enables a high power conversion efficiency of 18.6 % and good device stability.
Abstract
Electron transport materials (ETM) play an important role in the improvement of efficiency and stability for inverted perovskite solar cells (PSCs). This work reports an efficient ETM, named PDI‐C60, by the combination of perylene diimide (PDI) and fullerene. Compared to the traditional PCBM, this strategy endows PDI‐C60 with slightly shallower energy level and higher electron mobility. As a result, the device based on PDI‐C60 as electron transport layer (ETL) achieves high power conversion efficiency (PCE) of 18.6 %, which is significantly higher than those of the control devices of PCBM (16.6 %) and PDI (13.8 %). The high PCE of the PDI‐C60‐based device can be attributed to the more matching energy level with the perovskite, more efficient charge extraction, transport, and reduced recombination rate. To the best of our knowledge, the PCE of 18.6 % is the highest value in the PSCs using PDI derivatives as ETLs. Moreover, the device with PDI‐C60 as ETL exhibits better device stability due to the stronger hydrophobic properties of PDI‐C60. The strategy using the PDI/fullerene hybrid provides insights for future molecular design of the efficient ETM for the inverted PSCs.
Author(s): Rui Wang, Jingjing Xue, Lei Meng, Jin-Wook Lee, Zipeng Zhao, Pengyu Sun, Le Cai, Tianyi Huang, Zhengxu Wang, Zhao-Kui Wang, Yu Duan, Jonathan Lee Yang, Shaun Tan, Yonghai Yuan, Yu Huang, Yang Yang
Context & Scale
To overcome the barrier of the commercialization of metal halide perovskite solar cells, a simple, cost-effective, and generalized strategy that mitigates the intrinsic thermal instability is strongly needed. Here, caffeine is introduced to simultaneously enhance the efficiency and thermal stability of the solar cells based on various kinds of perovskite materials. The strong interaction between caffeine and Pb2+ ions serves as a “molecular lock” that increases the activation energy during film crystallization, delivering a perovskite film with preferred orientation, improved electronic properties, reduced ion migration, and greatly enhanced thermal stability. Ultimately, a champion-stabilized efficiency of 19.8% with 1,300 h thermal stability at 85°C in nitrogen was achieved.
Summary
To increase the commercial prospects of metal halide perovskite solar cells, there is a need for simple, cost-effective, and generalized approaches that mitigate their intrinsic thermal instability. Here we show that 1,3,7-trimethylxanthine, a commodity chemical with two conjugated carboxyl groups better known by its common name caffeine, improves the performance and thermal stability of perovskite solar cells based on both MAPbI3 and CsFAMAPbI3 active layers. The strong interaction between caffeine and Pb2+ ions serves as a “molecular lock” that increases the activation energy during film crystallization, delivering a perovskite film with preferred orientation, improved electronic properties, reduced ion migration, and greatly enhanced thermal stability. Planar n-i-p solar cells based on caffeine-incorporated pure MAPbI3 perovskites, which are notoriously unstable, exhibit a champion-stabilized efficiency of 19.8% and retain over 85% of their efficiency under continuous annealing at 85°C in nitrogen.
Author(s): Waqas Siddique Subhani, Kai Wang, Minyong Du, Shengzhong Frank Liu
Abstract
All-inorganic Br-rich perovskite photovoltaics with excellent stability have gained ever-increasing attention despite their slightly lower efficiency. Nowadays, trace heteroatom substitution has become a plausible approach to optimize perovskite properties as well as device performance. However, the substitution is limited by the Goldschmidt tolerance factor (t, 0.8 < t < 1.0), leading to the situation that the alternative deviating from the Goldschmidt rule is always overlooked, let alone utilized to enhance performance. Given this, Ba(II) is partially substituted for Pb(II) in CsPbIBr2 to investigate how the dopants-induced deviation from the Goldschmidt rule would affect perovskite property. Intriguingly, the result verifies that Ba(II) enables increased the grain size and enhances the crystallinity of CsPbIBr2. As such, the trap state density is reduced and the non-radiative recombination in the perovskite is suppressed. These advantages bring about an increase of the power conversion efficiency (PCE) of Ba(II)-doped devices to 10.51%, outperforming that (8.4%) of the pristine counterpart. In addition, the perovskite stability is immune to Ba(II) substitution, even though it inflates the perovskite crystal lattice. These findings indicate that the perovskite films are tolerant to homovalent heteroatoms with a larger radius, stimulating further development of perovskite substitution engineering.
Author(s): Kai Wang, Luyao Zheng, Tao Zhu, Xiang Yao, Chao Yi, Xiaotao Zhang, Yu Cao, Lei Liu, Wenping Hu, Xiong Gong
Abstract
Recently, hybrid perovskite materials have emerged as attractive alternatives for realizing cost-effective efficient perovskite solar cells. To date, impressive efficiency has been realized from the state-of-the-art solar cells through generic interface engineering and film morphological manipulation of perovskite active-layer in macroscopic scale. To further boost the efficiency of perovskite solar cells, microscopically tuning optoelectronic properties of hybrid perovskite materials represents a promising direction. In this study, we report efficient perovskite solar cells by a novel hybrid perovskites material that is incorporated with heterovalent neodymium cations (Nd3+). As compared with pristine hybrid perovskite materials, Nd3+-doped hybrid perovskite materials possess superior film quality with highly reduced trap-states, significantly enlarged charge carrier lifetimes, dramatically enhanced and balanced charge carrier mobilities. As a result, planar heterojunction perovskite solar cells by Nd3+-doped hybrid perovskite materials exhibit highly reproducible power conversion efficiency of 21.15% and significantly suppressed photocurrent hysteresis. These findings open a new window of tuning the optoelectronic properties of hybrid perovskite materials and boosting the device performance of perovskite solar cells. 21.15% power conversion efficiency and significantly suppressed photocurrent hysteresis were demonstrated from planar heterojunction perovskite solar cell using heterovalent neodymium cation doped hybrid perovskite materials.
Open Access
