Symmetry breaking provides a new material design strategy for nonfullerene small molecule acceptors (SMAs). The past 10 years have witnessed significant advances in asymmetric nonfullerene SMAs in organic solar cells (OSCs). In this review, the progress of asymmetric nonfullerene SMAs is reviewed. The structure–property relationships and the perspectives for future development of asymmetric non‐fullerene SMAs are also discussed.
Abstract
Symmetry breaking provides a new material design strategy for nonfullerene small molecule acceptors (SMAs). The past 10 years have witnessed significant advances in asymmetric nonfullerene SMAs in organic solar cells (OSCs) with power conversion efficiency (PCE) increasing from ≈1% to ≈14%. In this review, the progress of asymmetric nonfullerene SMAs, including early reports of asymmetric nonfullerene SMAs, asymmetric PDI‐based nonfullerene SMAs, and asymmetric acceptor–donor–acceptor (A–D–A)‐type nonfullerene SMAs, is summarized. The structure–property relationships and the perspectives for future development of asymmetric nonfullerene SMAs are also discussed.
Porous molecular crystals are easy to fabricate but thought to have limited stability as they are bound by non-covalent interactions. Here, a porous crystal composed of C60 and phthalocyanine is demonstrated with stability to heat, acid, base and high pressures.
Irrespective of the success on reduction of contact resistivity, lack of chemical passivation of evaporated metal oxides heavily hinders their applications as passivating contacts, such contacts can be an alternative route for high efficiency and cost effective silicon solar cells. Here, we demonstrate that electron beam evaporated magnesium oxide (MgOx) thin film can work as a promising electron-selective passivating contact for n-Si solar cells after a post-annealing treatment and an alumina-initiated atomic hydrogenation. 10 nm MgOx on n-Si provided a surface recombination velocity down to 14.9 cm/s while 1 nm MgOx showed a low contact resistivity of 14 mΩ cm2. Comprehensive characterizations revealed the formation of Si–O–Mg bonds and the activation of atomic hydrogens were the main reasons for such high-level passivation. A PERC-like dopant-free rear contact was formed by using the 1 nm-MgOx as electron-collector and the 10 nm-MgOx as passivating layer, the resultant solar cells achieved 27% increment in efficiency and 51 mV increase in open-circuit voltage in comparison with reference devices. The ways of improving passivation quality of MgOx and novel design of contact structure open up the possibility of using evaporation-processed metal oxides as effective and low-cost carrier-selective passivating contacts for n-Si photovoltaic devices.
Graphical abstract
Effective passivation over c-Si substrates by electron beam deposited MgOx followed by a low-temperature post-annealing and an alumina-initiated atomic hydrogen passivation has been achieved. a PERC-like dopant-free rear contact with 1 nm-MgOx as electron-transporting layer and 10 nm-MgOx as passivating layer was fabricated to underscore the great potential of MgOx passivating contact.
Organic n‐type materials as electron transport layers (ETLs) in inverted perovskite solar cells (p–i–n PSCs) have attracted many scientists' attention, not only because of their several advantages, including easy synthesis, tunable frontier molecular orbitals, decent electron mobility, and reasonable chemical/thermal stability, but also because of their ability to make large‐scale solution‐processing p–i–n PSCs possible.
Abstract
Organic n‐type materials (e.g., fullerene derivatives, naphthalene diimides (NDIs), perylene diimides (PDIs), azaacene‐based molecules, and n‐type conjugated polymers) are demonstrated as promising electron transport layers (ETLs) in inverted perovskite solar cells (p–i–n PSCs), because these materials have several advantages such as easy synthesis and purification, tunable frontier molecular orbitals, decent electron mobility, low cost, good solubility in different organic solvents, and reasonable chemical/thermal stability. Considering these positive factors, approaches toward achieving effective p–i–n PSCs with these organic materials as ETLs are highlighted in this Review. Moreover, organic structures, electron transport properties, working function of electrodes caused by ETLs, and key relevant parameters (PCE and stability) of p–i–n PSCs are presented. Hopefully, this Review will provide fundamental guidance for future development of new organic n‐type materials as ETLs for more efficient p–i–n PSCs.
High‐performance inverted lead‐free perovskite solar cells (PVSCs) with enhanced UV stability are demonstrated via grain boundaries modification by PTN‐Br. The gradient band alignment of FASnI3 films with a PEDOT:PSS hole‐transport layer ensures excellent hole transportation and higher open‐circuit voltage. This study provides a strategy to develop high‐performance tin‐based PVSCs based on balanced charge transportation and reduced trap states.
Abstract
High electronic quality perovskite films with a balanced charge transportation is critical for satisfying high‐performance for perovskite solar cells (PVSCs). However, the inferior band alignment of tin‐based perovskite films with an adjacent hole‐transport layer (HTL) leads to a poor hole transportation and collection. In this work, the semiconducting molecule poly[tetraphenylethene 3,3′‐(((2,2‐diphenylethene‐1,1‐diyl)bis(4,1‐phenylene))bis(oxy))bis(N,N‐dimethylpropan‐1‐amine)tetraphenylethene] (PTN‐Br) is introduced into a lead‐free perovskite precursor to form a bulk heterojunction film. In addition, the PTN‐Br molecule with the suitable highest occupied molecular orbital energy level (−5.41 eV) can fill into the grain boundaries of the perovskite film, serving as a hole‐transport medium between grains. The gradient band alignment of the perovskite film with poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HTL ensures excellent hole transportation and higher open‐circuit voltage. In addition, the π‐conjugated polymer PTN‐Br can passivate trap states within the perovskite film due to the formation of Lewis adducts between uncoordinated Sn atoms and the dimethylamino of PTN‐Br. Consequently, a champion efficiency of 7.94% is achieved with significant enhancements in the open‐circuit voltage and fill factor. Furthermore, the PTN‐Br incorporated device shows better ultra violet (UV) stability because of the UV barrier and passivating effect of PTN‐Br, retaining about 66% of its initial efficiency after 5 h of continuous UV light irradiation.
by Jueng‐Eun Kim,
Seok‐Soon Kim,
Chuantian Zuo,
Mei Gao,
Doojin Vak,
Dong‐Yu Kim
Roll‐to‐roll processed perovskite solar cells are fabricated using slot‐die coating by the hot deposition method. The hot deposition approach is scalable and can be performed in an uncontrolled ambient environment without additional processes. A polymer additive, polyethylene oxide, is introduced to improve the processability and proves useful for improving tolerance to humidity, resulting in improved reliability for industrial manufacturing.
Abstract
Heating‐assisted deposition is an industry‐friendly scalable deposition method. This manufacturing method is employed together with slot die coating to fabricate perovskite solar cells via a roll‐to‐roll process. The feasibility of the method is demonstrated after initial testing on a rigid substrate using a benchtop slot die coater in air. The fabricated solar cells exhibit power conversion efficiencies (PCEs) up to 14.7%. A nonelectroactive polymer additive is used with the perovskite formulation and found to improve its humidity tolerance significantly. These deposition parameters are also used in the roll‐to‐roll setup. The perovskite layer and other solution‐processed layers are slot die‐coated, and the fabricated device shows PCEs up to 11.7%, which is the highest efficiency obtained from a fully roll‐to‐roll processed perovskite solar cell to date.
by Tao Liu,
Wei Gao,
Yilin Wang,
Tao Yang,
Ruijie Ma,
Guangye Zhang,
Cheng Zhong,
Wei Ma,
He Yan,
Chuluo Yang
Unconjugated side‐chain engineering is performed on non‐fullerene small molecule acceptors based on a fused‐benzodithiophene core. Thieno[3,2‐b]thiophene is superior to thiophene and benzene owing to its dual roles of promoting the molecular energy level (δ‐inductive effect) and optimizing the morphology. Thus, organic solar cells based on PBDB‐T:BTTIC‐TT achieve the highest power conversion efficiency of 13.44% among three devices.
Abstract
2D conjugated side‐chain engineering is an effective strategy that is widely utilized to construct benzodithiophene‐based polymers. Herein, an unconjugated side‐chain strategy to design fused‐benzodithiophene‐based non‐fullerene small molecule acceptors (SMAs) via vertical aromatic side‐chain engineering on the ladder‐type core is employed. Three SMAs named BTTIC‐Th, BTTIC‐TT, and BTTIC‐Ph with thiophene, thieno[3,2‐b]thiophene, and benzene, respectively, as side chains, are designed and synthesized. Three SMAs exhibit similar absorption ranges but different lowest unoccupied molecular orbital (LUMO) energy levels due to the different strength of the δ‐inductive effect between vertical aromatic side chains and their electron‐rich core. Organic solar cells based on PBDB‐T:BTTIC‐TT achieve a power conversion efficiency (PCE) of 13.44%, which is higher than the PCE of devices based on PBDB‐T:BTTIC‐Th (12.91%) and PBDB‐T:BTTIC‐Ph (9.14%). The difference in device performance is investigated by electrical and morphological characterizations. A large domain size and different types of π–π stacking are found in the bulk heterojunction layer of PBDB‐T:BTTIC‐Ph blend film, which are detrimental to exciton dissociation and charge transport. Overall, it is demonstrated that when designing unconjugated side chains, thieno[3,2‐b]thiophene is superior to thiophene and benzene through its dual roles of promoting the LUMO energy level and optimizing the morphology. These results shed light on the side‐chain engineering of high‐performance non‐fullerene SMAs.
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 acquire 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 (PCE) 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%.
Surface‐clean and highly crystalline SnO2 ETL is fabricated by a simple hydrothermal treatment at temperatures as low as 100 °C. The perovskite solar cells based on this hydrothermally treated SnO2 ETL exhibit a champion PCE of 20.3% on a rigid ITO/Glass substrate, and a champion PCE of 18.1% and certified PCE of 17.3% on a flexible ITO/PEN substrate.
Abstract
Perovskite solar cells (PSCs) are one of the most promising solar energy conversion technologies owing to their rapidly developing power conversion efficiency (PCE). Low‐temperature solution processing of the perovskite layer enables the fabrication of flexible devices. However, their application has been greatly hindered due to the lack of strategies to fabricate high‐quality electron transport layers (ETLs) at the low temperatures (≈100 °C) that most flexible plastic substrates can withstand, leading to poor performances for flexible PSCs. In this work, through combining the spin‐coating process with a hydrothermal treatment method, ligand‐free and highly crystalline SnO2 ETLs are successfully fabricated at low temperature. The flexible PSCs based on this SnO2 ETL exhibit an excellent PCE of 18.1% (certified 17.3%). The flexible PSCs maintained 85% of the initial PCE after 1000 bending cycles and over 90% of the initial PCE after being stored in ambient air for 30 days without encapsulation. The investigation reveals that hydrothermal treatment not only promotes the complete removal of organic surfactants coated onto the surface of the SnO2 nanoparticles by hot water vapor but also enhances crystallization through the high vapor pressure of water, leading to the formation of high‐quality SnO2 ETLs.
by Saba Gharibzadeh,
Bahram Abdollahi Nejand,
Marius Jakoby,
Tobias Abzieher,
Dirk Hauschild,
Somayeh Moghadamzadeh,
Jonas A. Schwenzer,
Philipp Brenner,
Raphael Schmager,
Amir Abbas Haghighirad,
Lothar Weinhardt,
Uli Lemmer,
Bryce S. Richards,
Ian A. Howard,
Ulrich W. Paetzold
By coating n‐butylammonium bromide on wide‐bandgap double‐cation perovskite absorber layers (EG ≈ 1.72 eV), a thin 2D Ruddlesden–Popper perovskite layer of intermediate phase is formed. The resulting heterostructure mitigates nonradiative recombination and enables a high open‐circuit voltage of up to 1.31 V and stable power output efficiencies of up to 19.4%.
Abstract
In this work, the authors realize stable and highly efficient wide‐bandgap perovskite solar cells that promise high power conversion efficiencies (PCE) and are likely to play a key role in next generation multi‐junction photovoltaics (PV). This work reports on wide‐bandgap (≈1.72 eV) perovskite solar cells exhibiting stable PCEs of up to 19.4% and a remarkably high open‐circuit voltage (VOC) of 1.31 V. The VOC‐to‐bandgap ratio is the highest reported for wide‐bandgap organic−inorganic hybrid perovskite solar cells and the VOC also exceeds 90% of the theoretical maximum, defined by the Shockley–Queisser limit. This advance is based on creating a hybrid 2D/3D perovskite heterostructure. By spin coating n‐butylammonium bromide on the double‐cation perovskite absorber layer, a thin 2D Ruddlesden–Popper perovskite layer of intermediate phases is formed, which mitigates nonradiative recombination in the perovskite absorber layer. As a result, VOC is enhanced by 80 mV.
by Yang Wang,
Bin Liu,
Chang Woo Koh,
Xin Zhou,
Huiliang Sun,
Jianwei Yu,
Kun Yang,
Hang Wang,
Qiaogan Liao,
Han Young Woo,
Xugang Guo
A series of polycyclic aromatic hydrocarbon (PAH) cores with distinct π‐conjugation size are incorporated to construct a new family of fused‐ring electron acceptors (FREAs) via a simple and low‐cost synthetic route. The optoelectronic properties can be fine‐tuned at a molecular level over a wide range, which enables pyrene‐based DTP‐IC‐4Ph achieving a promising power conversion efficiency (PCE) of 10.37% in additive‐free nonfullerene organic solar cells.
Abstract
A series of polycyclic aromatic hydrocarbons (PAHs) with extended π‐conjugated cores (from naphthalene, anthracene, pyrene, to perylene) are incorporated into nonfullerene acceptors for the first time. Four different fused‐ring electron acceptors (FREAs), i.e., DTN‐IC‐2Ph, DTA‐IC‐3Ph, DTP‐IC‐4Ph, and DTPy‐IC‐5Ph, are prepared via simple and facile synthetic procedures, yielding a remarkable platform to study the structure–property relationship for nonfullerene solar cells. With the PAH core being extended systematically, the gradually redshifted absorption with enhanced molar extinction coefficient (ε) is realized, the energy level of the highest occupied molecular orbital is up‐shifted, and the electron mobility is greatly enhanced. Meanwhile, the solubility decreases and the molecular packing becomes strengthened. As a result, with an optimized combination of these characteristics, DTP‐IC‐4Ph attains good solubility, high molar extinction coefficient, complementary absorption, suitable morphology, well‐matched energy levels, as well as efficient charge dissociation and transport in blend film. Consequently, the DTP‐IC‐4Ph‐based solar cells with a donor polymer, poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene))‐alt‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethylhexyl)benzo[1′,2′‐c:4′,5′‐c′]dithiophene‐4,8‐dione))] (PBDB‐T) exhibit a promising power conversion efficiency of 10.37% without any additives, which is close to the best performance achieved in additive‐free nonfullerene solar cells (NFSCs). The results demonstrate that the PAH building blocks have great potential for the construction of novel FREAs for efficient additive‐free NFSCs.
Efficient electron transport layer‐free perovskite solar cells (ETL‐free PSCs) with cost‐effective and simplifed design can greatly promote the large area flexible application of PSCs. Within this review, the recent advancement, key issues, working mechanism, existing problems, and future direction of ETL‐free PSCs are summarized.
Abstract
Perovskite solar cells (PSCs) have shown great potential for photovoltaic applications with their unprecedented power conversion efficiency advancement. Such devices generally have a complex structure design with high temperature processed TiO2 as the electron transport layer (ETL). Further careful design of device configuration to fully tap the potentials of perovskite materials is expected. Particularly, for the practical application of PSCs, it is crucial to simplify their device structures thus the associated manufacturing process and cost while maintaining their efficiency to be comparable with the conventional devices. But how simple is simple? ETL‐free PSCs promise the simplest structured, thus simple manufacturing processes and low cost large area PSCs in practical applications. They can also help the further exploration of the great potential of perovskite materials and understanding the working principle of PSCs. Within this review, the evolution of the PSC is outlined by discussing the recent advances in the simplification of device configuration and processes for cost effective, highly efficient, and robust PSCs, with a focus on ETL‐free PSCs. Their advancement, key issues, working mechanism, existing problems, and future performance enhancements. This review aims to promote the future development of low cost and robust ETL‐free PSCs toward more efficient power output.
by Xiaomei Lian,
Jiehuan Chen,
Minchao Qin,
Yingzhu Zhang,
Tian Shuoxun,
Xinhui Lu,
Gang Wu,
Hongzheng Chen
High‐quality two‐dimensional perovskite film: Phenylethylammonium iodide (PEAI) added in a precursor solution can induce aggregation. The precursor aggregates are favorable for the formation of two‐dimensional Ruddlesden–Popper perovskite films with enlarged grain size over 1 mm and preferential orientation growth. The PCE of the solar cells are dramatically improved from 2.32 % (0 PEAI) to 14.09 % (0.1 PEAI).
Abstract
The fabrication of high‐quality film with large grains oriented along the direction of film thickness is important for 2D Ruddlesden–Popper perovskite‐based solar cells (PVSCs). High‐quality 2D BA2MAn−1PbnI3n+1 (BA+=butylammonium, MA+=methylammonium, n=5) perovskite films were fabricated with a grain size of over 1 μm and preferential orientation growth by introducing a second spacer cation (SSC+) into the precursor solution. Dynamic light scattering showed that SSC+ addition can induce aggregation in the precursor solution. The precursor aggregates are favorable for the formation of large crystal grains by inducing nucleation and decreasing the nucleation sites. Applying phenylethylammonium as SSC+, the optimized inverted planar PVSCs presented a maximum PCE of 14.09 %, which is the highest value of the 2D BA2MAn−1PbnI3n+1 (n=5) PVSCs. The unsealed device shows good moisture stability by maintaining around 90 % of its initially efficiency after 1000 h exposure to air (Hr=25±5 %).
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
Nanoscale, 2019, 11,12507-12516 DOI: 10.1039/C9NR02903F, Paper
Yi-June Huang, Yong-Jie Lin, Hung-Jei Chien, Yi-Feng Lin, Kuo-Chuan Ho The best carbon aerogel CE gives an η of 9.08% at 100 mW cm−2 and 20.1% at 2.18 mW cm−2. The content of this RSS Feed (c) The Royal Society of Chemistry
by Lirong Wu,
Jiaming Huang,
Yangyang Xie,
Ling Hong,
Ruixiang Peng,
Wei Song,
Like Huang,
Liqiang Zhu,
Wengang Bi,
Ziyi Ge
CdSe/ZnS quantum dots (QDs) are used as the cathode interlayer (CIL) modifier to enhance the power conversion efficiency of organic solar cells (OSCs) from 13.0% to 14.6% by improving the open‐circuit voltage (Voc) and short‐circuit current density (Jsc). The highest reported performance in QD‐modified OSCs is achieved.
Interfacial engineering plays an important role to improve the photovoltaic performance of organic solar cells (OSCs). Herein, CdSe/ZnS quantum dots (QDs) are used as a cathode interlayer (CIL) modifier. By using this strategy, an enhanced power conversion efficiency (PCE) from 13.0% to 14.6% is achieved, mainly due to the increase in open‐circuit voltage (Voc) and short‐circuit current density (Jsc). A single QD layer of a proper size can reduce the defects on the surface of the active layer and smoothen the interface between the active layer and cathode. Furthermore, the low work function of the QDs with dipole moment facilitates charge transport and suppresses charge recombination at the interface by strengthening the built‐in field, thus contributing to the enhancement of PCE. The excitons generated by the QDs can also be dissociated at the IT‐4F/QD interface, which boosts the photon harvesting capability of the device. As a result, a high PCE of 14.6% is achieved for QD‐modified OSCs.
by Nan‐Nan Chen,
Gan Jin,
Li‐Jing Wang,
He‐Nan Sun,
Qing‐Sen Zeng,
Bai Yang,
Hai‐Zhu Sun
A thicker bulk heterojunction film is successfully fabricated leading to generation of more carriers, extendsion of depleted region width, prolonged carrier lifetime, and improved carrier extraction efficiency. The highest short current density of 19.5 mA cm−2, power conversion efficiency of 6.51% and the widest depletion region (177 nm) are obtained based on aqueous‐processed hybrid solar cells.
Abstract
Environmental friendly aqueous‐processed solar cells have become one of the most promising candidates for the next‐generation photovoltaic devices. Researchers have made lots of progress in designing active materials with novel structures, manipulating the defects in active materials, optimizing device architecture, etc. However, it has long been a challenge to control the width of the depletion region and enhance carrier extraction ability. Fabrication of a thick bulk heterojunction (BHJ) film is an effective strategy to address these issues but difficult to realize. Herein, the thicker BHJ film of ZnO:CdTe is successfully fabricated and incorporated into CdTe‐poly(p‐phenylenevinylene) hybrid solar cells. As expected, this BHJ film enhances light absorption, extends the width of the depletion region, prolongs carrier lifetime, and promotes carrier extraction ability. Moreover, the electron transport layer of sol–gel ZnO with excellent transmittance and electrical conductivity boosts electron generation, transport, and injection, which further improves the device performance. As a result, the highest short current density (Jsc) of 19.5 mA cm−2, power conversion efficiency of 6.51%, and the widest depletion region (177 nm) are obtained in aqueous‐processed hybrid solar cells.
J. Mater. Chem. C, 2019, 7,5235-5243 DOI: 10.1039/C8TC04231D, Paper
Arthur Connell, Zhiping Wang, Yen-Hung Lin, Peter C. Greenwood, Alan A. Wiles, Eurig W. Jones, Leo Furnell, Rosie Anthony, Christopher P. Kershaw, Graeme Cooke, Henry J. Snaith, Peter J. Holliman Organic hole-transporting materials (HTM) have shown excellent ability in achieving high efficiency perovskite solar cells. The content of this RSS Feed (c) The Royal Society of Chemistry
by Kai Wang,
Marios Neophytou,
Erkan Aydin,
Mingcong Wang,
Thomas Laurent,
George T. Harrison,
Jiang Liu,
Wenzhu Liu,
Michele De Bastiani,
Jafar I. Khan,
Thomas D. Anthopoulos,
Frédéric Laquai,
Stefaan De Wolf
The small organic molecule (2‐(1,10‐phenanthrolin‐3‐yl)naphth‐6‐yl)diphenylphosphine oxide is explored as cathode interfacial material to reduce the extraction barrier between phenyl‐C61‐butyric acid methyl ester and Ag. With the better contact quality thanks to this molecule, both opaque and semitransparent p‐i‐n perovskite solar cell achieve improved performance and stability.
Abstract
Metal halide perovskite solar cells (PSCs) in the inverted planar p‐i‐n configuration often employ phenyl‐C61‐butyric acid methyl ester (PC61BM) as electron transport layer, onto which Ag is deposited as outer electrode. However, the energy offset between PC61BM and Ag imposes an energy barrier for electron extraction. In this work, to improve the contact quality of this stack, a small organic molecule (2‐(1,10‐phenanthrolin‐3‐yl)naphth‐6‐yl)diphenylphosphine oxide (DPO) as a cathode interfacial material (CIM), inserted between PC61BM and Ag, is introduced. In devices with the indium tin oxide (ITO)/NiOx/methylammonium lead iodide (MAPbI3)/PC61BM/CIM/Ag configuration, it is found that this results in fill factor (FF) and short‐circuit current density values (JSC) that are up to ≈34% and ≈1 mA cm−2 higher, respectively, compared to DPO‐free devices. Inserting additional thin ZnO nanoparticle layers further improves the contact quality, leading to a power conversion efficiency of 18.2%. Semitransparent PSCs, utilizing DPO as an interlayer buffer layer are also realised. Resultant devices exhibit improved performance compared to DPO‐free devices. This proves that DPO withstands the sputtering of ITO, and may thus find application in perovskite‐based tandem devices. It is concluded that DPO acts as an excellent cathode modifier, opening new device‐engineering opportunities for p‐i‐n PSCs, especially in their semitransparent implementation.
Organic n‐type materials as electron transport layers (ETLs) in inverted perovskite solar cells (p–i–n PSCs) have attracted many scientists' attention, not only because of their several advantages, including easy synthesis, tunable frontier molecular orbitals, decent electron mobility, and reasonable chemical/thermal stability, but also because of their ability to make large‐scale solution‐processing p–i–n PSCs possible.
Abstract
Organic n‐type materials (e.g., fullerene derivatives, naphthalene diimides (NDIs), perylene diimides (PDIs), azaacene‐based molecules, and n‐type conjugated polymers) are demonstrated as promising electron transport layers (ETLs) in inverted perovskite solar cells (p–i–n PSCs), because these materials have several advantages such as easy synthesis and purification, tunable frontier molecular orbitals, decent electron mobility, low cost, good solubility in different organic solvents, and reasonable chemical/thermal stability. Considering these positive factors, approaches toward achieving effective p–i–n PSCs with these organic materials as ETLs are highlighted in this Review. Moreover, organic structures, electron transport properties, working function of electrodes caused by ETLs, and key relevant parameters (PCE and stability) of p–i–n PSCs are presented. Hopefully, this Review will provide fundamental guidance for future development of new organic n‐type materials as ETLs for more efficient p–i–n PSCs.
by Meng Li,
Ying‐Guo Yang,
Zhao‐Kui Wang,
Tin Kang,
Qiong Wang,
Silver‐Hamill Turren‐Cruz,
Xing‐Yu Gao,
Chain‐Shu Hsu,
Liang‐Sheng Liao,
Antonio Abate
Embracing perovskite grains in a soft fullerene network represents a new and scalable approach, to make perovskite mechanically stable and thus compatible with flexible substrates. The method is demonstrated to prepare flexible perovskite solar cells with the highest ever reported power conversion efficiency. The superior mechanical stability from device performance under working conditions is characterized in situ.
Abstract
Halide perovskite films processed from solution at low‐temperature offer promising opportunities to make flexible solar cells. However, the brittleness of perovskite films is an issue for mechanical stability in flexible devices. Herein, photo‐crosslinked [6,6]‐phenylC61‐butyric oxetane dendron ester (C‐PCBOD) is used to improve the mechanical stability of methylammonium lead iodide (MAPbI3) perovskite films. Also, it is demonstrated that C‐PCBOD passivates the grain boundaries, which reduces the formation of trap states and enhances the environmental stability of MAPbI3. Thus, MAPbI3 perovskite solar cells are prepared on solid and flexible substrates with record efficiencies of 20.4% and 18.1%, respectively, which are among the highest ever reported for MAPbI3 on both flexible and solid substrates. The result of this work provides a step improvement toward stable and efficient flexible perovskite solar cells.
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
Defects in metal halide perovskites contribute to nonradiative recombination of photo‐carriers. On device level, such recombination undesirably inflates the open‐circuit voltage deficit and acts as a significant roadblock toward the theoretical efficiency limit of 30% perovskite solar cells. Such voltage‐limiting mechanisms are assessed by focusing on their origin and possible mitigation strategies.
Abstract
Metal‐halide perovskites are rapidly emerging as an important class of photovoltaic absorbers that may enable high‐performance solar cells at affordable cost. Thanks to the appealing optoelectronic properties of these materials, tremendous progress has been reported in the last few years in terms of power conversion efficiencies (PCE) of perovskite solar cells (PSCs), now with record values in excess of 24%. Nevertheless, the crystalline lattice of perovskites often includes defects, such as interstitials, vacancies, and impurities; at the grain boundaries and surfaces, dangling bonds can also be present, which all contribute to nonradiative recombination of photo‐carriers. On device level, such recombination undesirably inflates the open‐circuit voltage deficit, acting thus as a significant roadblock toward the theoretical efficiency limit of 30%. Herein, the focus is on the origin of the various voltage‐limiting mechanisms in PSCs, and possible mitigation strategies are discussed. Contact passivation schemes and the effect of such methods on the reduction of hysteresis are described. Furthermore, several strategies that demonstrate how passivating contacts can increase the stability of PSCs are elucidated. Finally, the remaining key challenges in contact design are prioritized and an outlook on how passivating contacts will contribute to further the progress toward market readiness of high‐efficiency PSCs is presented.
by Xiaomei Lian,
Jiehuan Chen,
Minchao Qin,
Yingzhu Zhang,
Tian Shuoxun,
Xinhui Lu,
Gang Wu,
Hongzheng Chen
High‐quality two‐dimensional perovskite film: Phenylethylammonium iodide (PEAI) added in a precursor solution can induce aggregation. The precursor aggregates are favorable for the formation of two‐dimensional Ruddlesden–Popper perovskite films with enlarged grain size over 1 mm and preferential orientation growth. The PCE of the solar cells are dramatically improved from 2.32 % (0 PEAI) to 14.09 % (0.1 PEAI).
Abstract
The fabrication of high‐quality film with large grains oriented along the direction of film thickness is important for 2D Ruddlesden–Popper perovskite‐based solar cells (PVSCs). High‐quality 2D BA2MAn−1PbnI3n+1 (BA+=butylammonium, MA+=methylammonium, n=5) perovskite films were fabricated with a grain size of over 1 μm and preferential orientation growth by introducing a second spacer cation (SSC+) into the precursor solution. Dynamic light scattering showed that SSC+ addition can induce aggregation in the precursor solution. The precursor aggregates are favorable for the formation of large crystal grains by inducing nucleation and decreasing the nucleation sites. Applying phenylethylammonium as SSC+, the optimized inverted planar PVSCs presented a maximum PCE of 14.09 %, which is the highest value of the 2D BA2MAn−1PbnI3n+1 (n=5) PVSCs. The unsealed device shows good moisture stability by maintaining around 90 % of its initially efficiency after 1000 h exposure to air (Hr=25±5 %).
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 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%.
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.
