Herein, allylammonium cations (CH2CH2CH3NH3 +) are incorporated into tin‐based perovskite to induce a preferred crystal orientation, leading to enhanced carrier transport and reduced trap density in the lead‐free films. The photovoltaic devices with an optimized perovskite layer exhibit a high power conversion efficiency of 9.48% and improved stability.
The low power conversion efficiency (PCE) of tin‐based perovskite solar cells is mainly caused by severe Sn2+ oxidation and trap state formation. Herein, the reduction of Sn4+ content and trap density is realized through the formation of quasi‐2D tin‐based perovskite by incorporating allylammonium (ALA) cations into formamidinium tin iodide (FASnI3). The composition modification substantially enhances the crystallinity and morphology of the perovskite films, leading to a preferred crystal orientation that facilitates charge carrier transport. After optimization, a high maximum PCE of 9.48% is achieved in a planar p‐i‐n photovoltaic device based on (ALA)2(FA) n−1Sn n X3n+1 (<n> = 25). In the meantime, the device also shows improved stability compared with the FASnI3‐based one.
An ultra‐flexible and transparent biomass‐derived conductive substrate is fabricated from polylactic acid. It exhibits high mechanical durability even when subjected to 15 000 bending cycles. Perovskite solar cells based on the biomass electrodes show good mechanical stability, retaining over 86% of its original power conversion efficiency after bending 1500 times at a curvature radius of 5 mm.
Biomass substrates are urgently needed to develop green electronics. Herein, an ultra‐flexible and transparent biomass‐derived conductive substrate is originated from nature polylactic acid (PLA) with silver nanowires (AgNWs) modified by PH1000. The composite electrode exhibits low sheet resistance of 25 Ω sq−1, high transmittance (over 82% in the region of 400–800 nm), and excellent mechanical durability. After bending tests of 15 000 times at a curvature radius of 3 and 5 mm, the sheet resistances of the composite electrodes only increase to 89 and 51 Ω sq−1, respectively. Biomass electrode–based flexible perovskite solar cells are demonstrated with a champion power conversion efficiency (PCE) of 11.44% and high bending tolerance with preserving over 86% of the initial PCE after 1500 bending cycles at a curvature radius of 5 mm. The biomass electrode exhibits great potential for the development of green flexible devices.
Water is added into the precursor solution to assist crystal growths of quasi‐2D perovskite films featuring ordered phase distribution and favored crystal orientation. A champion efficiency of 18.04% is realized in (BA)2(MA0.8FA0.15Cs0.05)4Pb5I16‐based quasi‐2D perovskite solar cells.
Organic–inorganic hybrid quasi‐2D perovskites have shown excellent stability for perovskite solar cells (PSCs), while the poor charge transport in quasi‐2D perovskites significantly undermines their power conversion efficiency (PCE). Here, studies on water‐controlled crystal growth of quasi‐2D perovskites are presented to achieve high‐efficiency solar cells. It is demonstrated that the (BA)2MA4Pb5I16‐based PSCs (n = 5) processed with water‐containing precursors display an increased short‐circuit current density (J sc) of 19.01 mA cm−2 and PCE over 15%. The enhanced performance is attributed to synergetic growths of the 3D and 2D phase components aided by the formed hydration (MAI∙H2O), leading to modulations on the crystal orientation and phase distribution of various n‐value components, which facilitate interphase charge transfer and charge sweepout throughout the device. The water‐assisted crystallization is further applied to triple cation‐based (BA)2(MA0.8FA0.15Cs0.05)4Pb5I16 quasi‐2D perovskites, which generate a remarkable PCE of 18.04%. Despite the presence of water in the precursors, the devices exhibit a satisfactory thermal stability with the PCE degradation <15% under continuous thermal aging at 60 °C for over 500 h.
A homochiral molecular ferroelectric was incorporated into a perovskite film to enlarge the built‐in electric field of the perovskite solar cell (PSC), thereby facilitating charge separation and transportation. The molecular ferroelectric component of the PSC passivates the defects in the perovskite active layers to induce an approximately eightfold enhancement in photoluminescence intensity and a reduction in electron trap‐state density.
The nonradiative recombination of electrons and holes has been identified as the main cause of energy loss in hybrid organic–inorganic perovskite solar cells (PSCs). Sufficient built‐in field and defect passivation can facilitate effective separation of electron–hole pairs to address the crucial issues. For the first time, we introduce a homochiral molecular ferroelectric into a PSC to enlarge the built‐in electric field of the perovskite film, thereby facilitating effective charge separation and transportation. As a consequence of similarities in ionic structure, the molecular ferroelectric component of the PSC passivates the defects in the active perovskite layers, thereby inducing an approximately eightfold enhancement in photoluminescence intensity and reducing electron trap‐state density. The photovoltaic molecular ferroelectric PSCs achieve a power conversion efficiency as high as 21.78 %.
High‐temperature degradation of perovskite solar cells with spiro‐OMeTAD hole transport layer is investigated. The postdoping of the spiro‐OMeTAD layer by iodine released from an iodine‐containing perovskite layer at high temperature is discovered as one reason for the high‐temperature degradation. Using an iodine‐free perovskite absorber, thermally stable perovskite solar cells are demonstrated.
Organic–inorganic halide perovskites are promising as the light absorber of solar cells because of their efficient solar power conversion. An issue frequently occurring in perovskite solar cells (PSCs) with a hole transport layer of N,N‐di(4‐methoxyphenyl)amino]‐9,9′‐spirobifluorene (spiro‐OMeTAD) is a quick performance degradation at high temperature. Herein, it is discovered that postdoping of the spiro‐OMeTAD layer by iodine released from the perovskite layer is one possible mechanism for the high‐temperature PSC degradation. Iodine doping leads to the highest occupied molecular orbital level of the spiro‐OMeTAD layer becoming deeper and, therefore, induces the formation of an energy barrier for hole extraction from the perovskite layer. It is demonstrated that it is possible to suppress the high‐temperature degradation by using an iodine‐blocking layer or an iodine‐free perovskite in PSCs. These findings will guide the way for the realization of thermally stable perovskite optoelectronic devices in the future.
Saddle‐shaped small molecules α, β‐COTh‐Ph‐OMeTAD and β, β‐COTh‐Ph‐OMeTAD are synthesized and systemically characterized as dopant‐free hole‐transporting material (HTM) in inverted perovskite solar cells (i‐PSCs). High power conversion efficiencies (PCEs) (17.59% and 18.53%) and stable‐enhanced PSCs devices are achieved, and more than 80% of the maximum PCE is retained after storing in glove box for 150 days.
Two saddle‐shaped hole‐transporting materials (HTMs), α, β‐COTh‐Ph‐OMeTAD and β, β‐COTh‐Ph‐OMeTAD are designed with a strategy of flexible core with tunable conformation (FCTC) and applied in inverted planar perovskite solar cells (PSCs) as dopant‐free HTMs. As a result, the device based on α, β‐COTh‐Ph‐OMeTAD demonstrates a high power conversion efficiency (PCE) of 17.59% with J sc = 21.32 mA cm−2, V oc = 1.02 V, and FF = 80.75%, and the one based on β, β‐COTh‐Ph‐OMeTAD yields a higher PCE of 18.53% with J sc = 22.68 mA cm−2, V oc = 1.04 V, and FF = 78.48%. Moreover, the green‐solvent‐processed PSCs are also fabricated by dissolving the HTMs in ethyl acetate. Without any encapsulation, the devices based on both HTMs retain 80% of their initial PCEs after storage for 150 days in a glove box, and 60% of their initial PCEs after storing for 300 h in ambient air with 40% relative humidity. All these results demonstrate that the materials α, β‐COTh‐Ph‐OMeTAD and β, β‐COTh‐Ph‐OMeTAD based on FCTC strategy are promising HTMs for highly efficient and stable PSCs.
Crystallization tailoring (F− doping) of perovskite and construction of multilayer cascade charge transport layers (NiO x /Zn:CuGaO2 and TiO2/PC61BM/ZnO) for inverted CsPbI2Br solar cells are collaboratively presented, resulting in excellent device efficiency (over 15%) with improved stability. The present strategy can be extended to hybrid wide‐bandgap perovskite solar cells.
It is imperative to improve the quality of light absorber and reduce the charge‐carrier recombination for efficient perovskite solar cells (PSCs). Herein, a synergistic regulation strategy that combines the tailoring of crystallinity and construction of multilayer cascade charge transport layers (CTLs) for inverted CsPbI2Br solar cells is presented. The film quality of CsPbI2Br is well tuned via F− doping. In addition, gradient energy alignment between perovskite and CTLs, i.e., NiO x /Zn:CuGaO2/perovskite and perovskite/TiO2/PC61BM/ZnO, favors the charge transfer and depresses carrier recombination. Noticeably, the TiO2 interlayer with deep valence band maximum effectively blocks the hole back‐transfer from perovskite to PC61BM. These unique characteristics of the novel structured CsPbI2Br device give a champion power conversion efficiency (PCE) of 15.10% along with good thermal and operational stability. Moreover, the graded CTLs can be expanded to methylammonium‐free hybrid perovskite device (E g = ≈1.76 eV) by delivering a PCE of 18.12%, showing great promise in tandem solar cells for use as top cell.
An industry compatible slot‐die coating process combined with near‐infrared irradiation heating enables rapid manufacture of large‐area and uniform perovskite solar cells in air. The highest power conversion efficiency for a device, which is fabricated using the slot‐die coated four layer, is nearly 11%.
Currently, high‐efficiency perovskite solar cells are mainly fabricated by the spin‐coating process, which limits the possibility of commercial mass‐production of perovskite solar cells. In this work, the slot‐die coating process is combined with near‐infrared irradiation heating to quickly manufacture perovskite solar cells in air. The composition of the perovskite precursor solution is tuned by adding n‐butanol, with its low boiling point and low surface tension, to increase the near‐infrared energy absorption, facilitate the evaporation of the solvent system and film formation, and accelerate the crystallization of perovskite. High‐quality uniform perovskite film can be prepared within 18 s. Moreover, the all slot‐die coating process is demonstrated to prepare over an area of 12 cm × 12 cm, four layers of uniform film overlay on top of each other for the devices except electrode in ambient air. A power conversion efficiency of ≈11% is achieved when this all slot‐die coated film is used to fabricate device. This facile process can greatly reduce the cost, time and bypass post‐annealing to fabricate high‐efficiency large‐area perovskite solar cells in ambient air.
In article number https://doi.org/10.1002/aenm.2020007722000772, Siva Krishna Karuturi, Heping Shen and co‐workers report a perovskite/Si dual absorber tandem cell for stand‐alone solar water splitting. An unprecedented over 17% solar‐to hydrogen conversion efficiency is achieved when a Si photocathode is paired in tandem with a high bandgap (≈1.75 eV) semitransparent perovskite solar cell.
Barriers with compact morphology/structure and shielding capability can be designed/ integrated in perovskite solar cells to prevent issues like product volatilization, ion diffusion, electrode corrosion, and ingress of the harmful components brought about by the intrinsic interface failure or the attack of heat, sunlight, electric bias, and H2O/O2, leading to robust stability of the whole device.
Perovskite solar cells (PSCs) have attracted much attention in the past decade and their power conversion efficiency has been rapidly increasing to 25.2%, which is comparable with commercialized solar cells. Currently, the long‐term stability of PSCs remains as a major bottleneck impeding their future commercial applications. Beyond strengthening the perovskite layer itself and developing robust external device encapsulation/packaging technology, integration of effective barriers into PSCs has been recognized to be of equal importance to improve the whole device’s long‐term stability. These barriers can not only shield the critical perovskite layer and other functional layers from external detrimental factors such as heat, light, and H2O/O2, but also prevent the undesired ion/molecular diffusion/volatilization from perovskite. In addition, some delicate barrier designs can simultaneously improve the efficiency and stability. In this review article, the research progress on barrier designs in PSCs for improving their long‐term stability is reviewed in terms of the barrier functions, locations in PSCs, and material characteristics. Regarding specific barriers, their preparation methods, chemical/photoelectronic/mechanical properties, and their role in device stability, are further discussed. On the basis of these accumulative efforts, predictions for the further development of effective barriers in PSCs are provided at the end of this review.
A recast strategy is proposed to optimize the spatial distribution of components in organic bulk‐heterojunction (BHJ) films in an all‐inorganic perovskite/BHJ integrated solar cells, leading to extended photoresponse, enhanced ambipolar charge transport, and suppressed charge carrier recombination. A record power conversion efficiency of 11.08% and robust thermal stability are obtained.
All‐inorganic CsPbIBr2 perovskite solar cells (pero‐SCs) exhibit excellent overall stability, but their power conversion efficiencies (PCEs) are greatly limited by their wide bandgaps. Integrated solar cells (ISCs) are considered to be an emergent technology that could extend their photoresponse by directly stacking two distinct photoactive layers with complementary bandgaps. However, rising photocurrents always sacrifice other photovoltaic parameters, thereby leading to an unsatisfactory PCE. Here, a recast strategy is proposed to optimize the spatial distribution components of low‐bandgap organic bulk‐heterojunction (BHJ) film, and is combined with an all‐inorganic perovskite to construct perovskite/BHJ ISCs. With this strategy, the integrated perovskite/BHJ film with a top‐enriched donor‐material spatial distribution is shown to effectively improve ambipolar charge transport behavior and suppress charge carrier recombination. For the first time, the ISC is not only significantly extended and enhanced the photoresponse achieving a 20% increase in current density, but also exhibits a high open‐circuit voltage and fill factor at the same time. As a result, a record PCE of 11.08% based on CsPbIBr2 pero‐SCs is realized; it simultaneously shows excellent long‐term stability against heat and ultraviolet light.
A robust strategy for constructing flexible perovskite solar cells that can be conveniently biodegraded is introduced. The results signify the great potential of meniscus‐assisted solution printing for controllably assembling aligned conductive nanomaterials for biodegradable electrodes. As such, it represents an important endeavor toward environmentally friendly, multifunctional, and flexible electronics.
Increasing performance demand associated with the short lifetime of consumer electronics has triggered fast growth in electronic waste, leading to serious ecological challenges worldwide. Herein, a robust strategy for judiciously constructing flexible perovskite solar cells (PSCs) that can be conveniently biodegraded is reported. The key to this strategy is to capitalize on meniscus‐assisted solution printing (MASP) as a facile means of yielding cross‐aligned silver nanowires in one‐step, which are subsequently impregnated in a biodegradable elastomeric polyester. Intriguingly, the as‐crafted hybrid biodegradable electrode greatly constrains the solvent evaporation of the perovskite precursor solution, thereby generating fewer nuclei and in turn resulting in the deposition of a large‐grained dense perovskite film that exhibits excellent optoelectronic properties with a power conversion efficiency of 17.51% in PSCs. More importantly, the hybrid biodegradable electrode‐based devices also manifest impressive robustness against mechanical deformation and can be thoroughly biodegraded after use. These results signify the great potential of MASP for controllably assembling aligned conductive nanomaterials for biodegradable electrodes. As such, it represents an important endeavor toward environmentally friendly, multifunctional and flexible electronic, optoelectronic, photonic, and sensory materials and devices.
In article number https://doi.org/10.1002/adma.2020014762001476, Xugang Guo and co‐workers develop two ultranarrow‐bandgap n‐type polymer semiconductors, which enable efficient electron transport in organic thin‐film transistors with a highest electron mobility of 1.72 cm2 V−1 s−1 and which deliver remarkable photovoltaic performance with a highest power conversion efficiency of 10.22% and short‐circuit current up to 22.52 mA cm−2. The emergence of such polymers will guide materials innovation for realizing highperformance fully flexible all‐polymer solar cell modules.
In this paper, laboratory and rooftop performance of perovskite solar cells under changing temperature and irradiance is analyzed. By integrating laboratory data trends and measured weather data into optical energy yield model, the temperature‐dependent energy yield model is developed and validated, and can be used to predict generated energy of perovskite solar cells or track their degradation during field testing.
Perovskite solar cells (PSC) have shown that under laboratory conditions they can compete with established photovoltaic technologies. However, controlled laboratory measurements usually performed do not fully resemble operational conditions and field testing outdoors, with day‐night cycles, changing irradiance and temperature. In this contribution, the performance of PSCs in the rooftop field test, exposed to real weather conditions is evaluated. The 1 cm2 single‐junction devices, with an initial average power conversion efficiency of 18.5% are tracked outdoors in maximum power point over several weeks. In parallel, irradiance and air temperature are recorded, allowing us to correlate outside factors with generated power. To get more insight into outdoor device performance, a comprehensive set of laboratory measurements under different light intensities (10% to 120% of AM1.5) and temperatures is performed. From these results, a low power temperature coefficient of −0.17% K−1 is extracted in the temperature range between 25 and 85 °C. By incorporating these temperature‐ and light‐dependent PV parameters into the energy yield model, it is possible to correctly predict the generated energy of the devices, thus validating the energy yield model. In addition, degradation of the tested devices can be tracked precisely from the difference between measured and modelled power.
A new fluorinated organic ammonium halide salt, 4‐trifluoromethyl phenethylammonium iodide (CFPEAI), is utilized to passivate the surface of CsPbI2Br perovskite for solar cells with enhanced efficiency as well as improved stability.
Surface modification is demonstrated as an efficient strategy to enhance the efficiency and stability of perovskite solar cells (PVSCs). Fluorinated organic ammonium salts featuring a strong hydrophobic nature are seldom used as passivation agents for the surface modification of CsPbI2Br perovskites. Herein, a fluorinated organic ammonium halide salt, 4‐trifluoromethyl phenethylammonium iodide (CFPEAI), is incorporated into the surface of CsPbI2Br perovskite for the first time. After the CFPEAI modification, the defects of CsPbI2Br perovskite are significantly passivated with reduced trap densities. The best‐performance PVSC with CFPEAI modification shows an excellent power conversion efficiency (PCE) of 16.07% with a high fill factor (FF) of 84.65%, a short‐circuit current density (J SC) of 15.45 mA cm−2, and an open‐circuit voltage (V OC) of 1.23 V. In contrast, the control PVSCs without the surface modification exhibit a lower PCE of 14.50% with a FF of 80.56%, a J SC of 15.05 mA cm−2, and a V OC of 1.20 V. With CFPEAI passivation, the CsPbI2Br perovskite film exhibits enhanced hydrophobicity, thereby leading to improved stability for the corresponding PVSC in comparison with the control PVSC without any surface modification.
1‐Naphthylmethylammonium bromide (NMABr)passivates the surface of 3D perovskite by the in situ formation of a 2D/3D type‐II heterostructure. The 2D perovskite layer blocks the transfer of electrons, reduces the trap densities, and delivers better stability. As a result, NMABr‐passivated perovskite solar cells deliver a champion efficiency of 21.09% with enhanced stability.
Heterojunction engineering is essential to reduce energy loss and enhance the stability of perovskite solar cells (PSCs). Herein, 1‐naphthylmethylammonium bromide (NMABr) is introduced to in situ generate an ultrathin p‐type 2D perovskite with wide bandgap between the 3D perovskite film and the hole transport layer (HTL). Cascade 2D/3D perovskites in situ form a type‐II heterojunction, which largely contributes to the improvement of photovoltaic performance. The type‐II heterojunction not only blocks the electron transfer and reduces the charge recombination on the surface and grain boundaries of the 3D perovskite film, but also promotes the hole extraction. The microphotoluminescence indicates the reduction of nonradiative recombination on the surface, consistent with the reduced trap density in Mott–Schottky plots and the increased recombination resistance in impedance spectra. The champion power conversion efficiency (PCE) of the NMABr‐passivated 2D/3D PSC reaches 21.09% under the AM1.5 illumination. In addition, the NMABr‐passivated 2D/3D PSC remains 80% of the initial PCE for 105 h at 85 °C in nitrogen and retains 80% of initial PCE for 350 h in 70–80% relative humidity in the air. This work provides a crucial in situ fabrication of type‐II 2D/3D heterojunction to improve the stability and efficiency of PSCs.
A low‐temperature crystallization strategy of CsPbIBr2 perovskite solar cells is reported. The additive n‐butylammonium iodide (BAI) is incorporated into the perovskite precursor to improve crystallinity, optimize morphology, and passivate defects at 160 °C. As a result, a high‐level PCE of 10.78% with a high open‐circuit voltage (V OC) of 1.25 V is achieved.
Inorganic cesium lead halide perovskite solar cells (PSCs) have been widely explored due to their outstanding thermal stability and photovoltaic performance. However, the application and development of CsPbIBr2‐based PSCs is still hindered by major challenges such as high fabrication temperature and large voltage loss. To address these difficulties, additive engineering is conducted using n‐butylammonium iodide (BAI). It is found that it not only improves the crystallization and morphology of perovskite layers but also substantially decreases the annealing temperature. In addition, the BAI incorporation decreases trap state density and restrains nonradiative recombination. As such, a high power conversion efficiency (PCE) of 10.78% is achieved, 21% higher compared with that of the control sample (8.88%). It should be noted that this is particularly high for the CsPbIBr2 PSCs fabricated at low temperatures (<200 °C) that are required for flexible devices based on polymeric substrates.
Tandem solar cells hold promise for breaking the second law of thermodynamics and Shockley–Queisser limits. So far, such devices have to be made via costly methods. The advent of perovskite‐based absorbers enables the fabrication of various tandem devices through low‐cost techniques by combination with different subcells.
Tandem solar cells (TSCs) comprising stacked narrow‐bandgap and wide‐bandgap subcells are regarded as the most promising approach to break the Shockley–Queisser limit of single‐junction solar cells. As the game‐changer in the photovoltaic community, organic–inorganic hybrid perovskites became the front‐runner candidate for mating with other efficient photovoltaic technologies in the tandem configuration for higher power conversion efficiency, by virtue of their tunable and complementary bandgaps, excellent photoelectric properties, and solution processability. In this review, a perspective that critically dilates the progress of perovskite material selection and device design for perovskite‐based TSCs, including perovskite/silicon, perovskite/copper indium gallium selenide, perovskite/perovskite, perovskite/CdTe, and perovskite/GaAs are presented. Besides, all‐inorganic perovskite CsPbI3 with high thermal stability is proposed as the top subcell in TSCs due to its suitable bandgap of ≈1.73 eV and rapidly increasing efficiency. To minimize the optical and electrical losses for high‐efficiency TSCs, the optimization of transparent electrodes, recombination layers, and the current‐matching principles are highlighted. Through big data analysis, wide‐bandgap perovskite solar cells with high open‐circuit voltage (V oc) are in dire need in further study. In the end, opportunities and challenges to realize the commercialization of TSCs, including long‐term stability, area upscaling, and mitigation of toxicity, are also envisioned.
Layered hybrid perovskites based on (PDMA)FA n –1Pb n I3 n +1 (n = 1–3; PDMA = 1,4‐phenylenedimethanammonium) compositions are investigated by using combination of techniques, including X‐ray scattering measurements, molecular dynamics simulations, and density functional theory calculations, along with time‐resolved microwave conductivity measurements, to unravel unique structural and photophysical properties relevant to optoelectronic applications.
Layered hybrid perovskites have emerged as a promising alternative to stabilizing hybrid organic–inorganic perovskite materials, which are predominantly based on Ruddlesden‐Popper structures. Formamidinium (FA)‐based Dion‐Jacobson perovskite analogs are developed that feature bifunctional organic spacers separating the hybrid perovskite slabs by introducing 1,4‐phenylenedimethanammonium (PDMA) organic moieties. While these materials demonstrate competitive performances as compared to other FA‐based low‐dimensional perovskite solar cells, the underlying mechanisms for this behavior remain elusive. Here, the structural complexity and optoelectronic properties of materials featuring (PDMA)FA n –1Pb n I3 n +1 (n = 1–3) formulations are unraveled using a combination of techniques, including X‐ray scattering measurements in conjunction with molecular dynamics simulations and density functional theory calculations. While theoretical calculations suggest that layered Dion‐Jacobson perovskite structures are more prominent with the increasing number of inorganic layers (n), this is accompanied with an increase in formation energies that render n > 2 compositions difficult to obtain, in accordance with the experimental evidence. Moreover, the underlying intermolecular interactions and their templating effects on the Dion‐Jacobson structure are elucidated, defining the optoelectronic properties. Consequently, despite the challenge to obtain phase‐pure n > 1 compositions, time‐resolved microwave conductivity measurements reveal high photoconductivities and long charge carrier lifetimes. This comprehensive analysis thereby reveals critical features for advancing layered hybrid perovskite optoelectronics.
Publication date: November 2020
Source: Nano Energy, Volume 77
Author(s): Qian-Qian Chu, Zhijian Sun, Bin Ding, Kyoung-sik Moon, Guan-Jun Yang, Ching-Ping Wong
