Ligang Yuan

Four new polymers containing the novel asymmetrical backbone, thienobenzodithiophene, are synthesized and applied in high‐performance nonfullerene solar cells. The asymmetrical backbone can dramatically effect the polymer geometric configuration and modulate the polymer aggregation and crystallinity. This work reveals that the versatile asymmetric backbone is an excellent moiety to construct light‐harvesting copolymers and to modulate the microstructure for highly efficient PSCs.

Abstract

In this work, a new asymmetrical backbone thienobenzodithiophene (TBD) containing four aromatic rings is designed, and then four polymers PTBD‐BZ, PTBD‐BDD, PTBD‐FBT, and PTBD‐Tz are synthesized. The planar and high degree of π‐conjugation configuration can guarantee effective charge carrier transport and the distinct flanked dihedral angles between the TBD core and conjugated side chain can subtly regulate the molecular aggregation and crystallinity. The four polymer/3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone)‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]‐dithiophene (ITIC) blending films exhibit predominantly face‐on orientation. The photovoltaic devices based on wide bandgap polymers PTBD‐BZ and PTBD‐BDD achieve power conversion efficiencies (PCEs) as high as 12.02% and 11.39% without any post‐treatment. For the medium bandgap polymers PTBD‐FBT and PTBD‐Tz, the devices also show good PCEs of 10.18% and 11.02% with high V _OC of 0.94 and 1.02 V, respectively, which indicates simultaneously achieving a V _OC > 1 V and a high J _SC is feasible to further improve the PSCs' performance by modifying this new backbone. This work reveals that the versatile asymmetric backbone is an excellent moiety to construct light‐harvesting copolymers and to modulate the microstructure for highly efficient PSCs.

The absence of a charge transfer (CT) state is found in the (6,5) single‐walled carbon nanotube:PC₇₀BM system and a detailed analysis of the open‐circuit voltage (V _OC) is reported. The analysis reveals that the lack of the CT state enables very small radiative as well as nonradiative V _OC losses for an organic cell, despite the ultranarrow bandgap of this system.

Abstract

Current state‐of‐the‐art organic solar cells (OSCs) still suffer from high losses of open‐circuit voltage (V _OC). Conventional polymer:fullerene solar cells usually exhibit bandgap to V _OC losses greater than 0.8 V. Here a detailed investigation of V _OC is presented for solution‐processed OSCs based on (6,5) single‐walled carbon nanotube (SWCNT): [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester active layers. Considering the very small optical bandgap of only 1.22 eV of (6,5) SWCNTs, a high V _OC of 0.59 V leading to a low E _gap/q − V _OC = 0.63 V loss is observed. The low voltage losses are partly due to the lack of a measurable charge transfer state and partly due to the narrow absorption edge of SWCNTs. Consequently, V _OC losses attributed to a broadening of the band edge are very small, resulting in V _OC,SQ − V _OC,rad = 0.12 V. Interestingly, this loss is mainly caused by minor amounts of SWCNTs with smaller bandgaps as well as (6,5) SWCNT trions, all of which are experimentally well resolved employing Fourier transform photocurrent spectroscopy. In addition, the low losses due to band edge broadening, a very low voltage loss are also found due to nonradiative recombination, ΔV _OC,nonrad = 0.26 V, which is exceptional for fullerene‐based OSCs.

Hybrid solar cells incorporated with conjugated polyelectrolytes show the molecular rearrangement and vertical phase separation, which result from a molecular dipole between the conjugated backbone and the side chain. With the simple one‐pot coating process of fullerene based hybrid active layer, the power conversion efficiency reaches to 8.7% with the enhanced stability.

Abstract

Hybrid organic solar cells are made through a simple one‐pot coating process with conjugated polyelectrolytes (CPEs), poly[9,9‐bis(4′‐sulfonatobutyl)fluorenealt‐thiophene‐doped (PFT‐D). The hybrid active layer incorporated with PFT‐D shows vertical phase separation by self‐assembled properties of PFT‐D, which result from a molecular dipole between the conjugated backbone and the side chain. The hybrid active layer with PFT‐D shows that homogeneous morphology, surface potential properties, and hydrophobic surface properties favor for enhancing photovoltaic performance. These results are identified by contact angle characteristics, X‐ray photoelectron spectroscopy (XPS) profiling, and X‐ray diffraction (XRD), atomic force measurement (AFM), and electrostatic force measurement (EFM) analyses. With fullerene based hybrid active layer, the power conversion efficiency (PCE) reaches to 8.7% with the enhanced short‐circuit current density (J _SC), open‐circuit voltage (V _OC), and fill factor (FF). The hybrid device with PFT‐D has a higher stability with a lower reduction ratio of 5.74% compared with only bulk‐heterojunction device (with reduction rate of 30.15%) and incorporating poly(3,4‐ethylene dioxythiophene)‐poly(styrene sulfonate) (PEDOT:PSS) device (with reduction rate of 10.84%). These results are also found in nonfullerene based system (PCE of 10.8%) and other conjugated polyelectrolytes system (PCE of 8.4%). These results have the potential of significantly contributing to the upsizing and commercialization of organic solar cells.

A record‐high E‐field‐induced ferromagnetic resonance field shift of 1400 Oe is achieved in an yttrium iron garnet/Cu/Pt/ionic liquid/Au capacitor heterostructure with a small voltage bias of 4.5 V characterized via in situ electron spin resonance spectroscopy. The giant magnetoelectric tunability comes from voltage‐induced extra ferromagnetic ordering in the Cu layer, confirmed by the first‐principle calculation.

Abstract

Ferromagnetic insulator thin film nanostructures are becoming the key component of the state‐of‐the‐art spintronic devices, for instance, yttrium iron garnet (YIG) with low damping, high Curie temperature, and high resistivity is explored into many spin–orbit interactions related spintronic devices. Voltage modulation of YIG, with great practical/theoretical significance, thus can be widely applied in various YIG‐based spintronics effects. Nevertheless, to manipulate ferromagnetism of YIG through electric field (E‐field), instead of current, in an energy efficient manner is essentially challenging. Here, a YIG/Cu/Pt layered nanostructure with a weak spin–orbit coupling interaction is fabricated, and then the interfacial magnetism of the Cu and YIG is modified via ionic liquid gating method significantly. A record‐high E‐field‐induced ferromagnetic resonance field shift of 1400 Oe is achieved in YIG (17 nm)/Cu (5 nm)/Pt (3 nm)/ionic liquid/Au capacitor layered nanostructures with a small voltage bias of 4.5 V. The giant magnetoelectric tunability comes from voltage‐induced extra ferromagnetic ordering in Cu layer, confirmed by the first‐principle calculation. This E‐field modulation of interfacial magnetism between light metal and magnetic isolator may open a door toward compact, high‐performance, and energy‐efficient spintronic devices.

An ultrathin ferroelectric oxide PbTiO₃ layer is incorporated between the electron transport material and the halide perovskite in the hole transport material (HTM) free carbon‐based perovskite solar cell (C‐PSCs). The achieved power conversion efficiency is as high as 16.37%, which is the highest record for HTM‐free C‐PSCs to date, mainly ascribable to the ferroelectric layer enhanced open circuit voltage.

Abstract

The hole transport material (HTM) free carbon based perovskite solar cells (C‐PSCs) are promising for its manufactural simplicity, but they currently suffer from low power conversion efficiencies (PCE) largely because of the voltage loss. Here, a new strategy to increase the PCE by incorporating an ultrathin ferroelectric oxide PbTiO₃ layer between the electron transport material and the halide perovskite is reported. The resulting C‐PSCs have achieved PCEs up to 16.37%, which is the highest record for HTM‐free C‐PSCs to date, mainly ascribable to the ferroelectric layer enhanced open circuit voltage. Detail measurements and analysis show an enhanced built‐in potential in the C‐PSCs as well as suppression of the non‐radiative recombination due to the ferroelectric PbTiO₃ layer incorporation, accounting for the boosted V _OC and photovoltaic performance.

PbTiO₃ (PTO) with suitable band alignment is a promising electron‐selective layer in hybrid perovskite solar cells. Reversal of the local polarization of PTO upon alternating external poling can tune the transfer direction of the photogenerated carriers in the active layer, thereby improving the photovoltaic performance of the solar cells.

Abstract

PbTiO₃ (PTO) is explored as a versatile and tunable electron‐selective layer (ESL) for perovskite solar cells. To demonstrate effectiveness of PTO for electron–hole separation and charge transfer, perovskite solar cells are designed and fabricated in the laboratory with the PTO as the ESL. The cells achieve a power conversion efficiency (PCE) of ≈12.28% upon preliminary optimization. It is found that the PTO ferroelectric layer can not only increase the PCE, but also tune the photocurrent via tuning PTO's ferroelectric polarization. Moreover, to understand the physical mechanism underlying the carrier transport by the ferroelectric polarization, the electronic structure of PTO/CH₃NH₃PbI₃ heterostructure is computed using the first‐principles methods, for which the triplet state is used to simulate charge transfer in the heterostructure. It is shown that the synergistic effect of type II band alignment and the specific ferroelectric polarization direction provide the effective extraction of electrons from the light absorber, while minimize recombination of photogenerated electron–hole pairs. Overall, the ferroelectric PTO is a promising and tunable ESL for optimizing electron transport in the perovskite solar cells. The design offers a different strategy for altering direction of carrier transport in solar cells.

A new method to control current–voltage hysteresis of planar structured FA_0.83Cs_0.17PbI₃ perovskite solar cells (PSCs) is presented while enhancing device efficiency through tailoring the crystal structure of the perovskite compound with a guanidinium cation (Gu⁺)‐dopant. New insights into the correlation of the dynamics of device hysteresis with the interfacial charge recombination and accumulation in the PSCs are revealed.

Abstract

Current–voltage hysteresis of perovskite solar cells (PSCs) has raised the concern of accurate performance measurement in practice. Although various theories have been proposed to elucidate this phenomenon, the origin of hysteresis is still an open question. Herein, the use of guanidinium cation (Gu⁺)‐dopant is demonstrated to tailor the crystal structure of mixed‐cation formamidinium‐cesium lead triiodide (FA_0.83Cs_0.17PbI₃) perovskite, resulting in an improved energy conversion efficiency and tunable current–voltage hysteresis characteristic in planar solar cells. Particularly, when the concentration of Gu‐dopant for the perovskite film increases, the normal hysteresis initially observed in the pristine PSC is first suppressed with 2%‐Gu‐dopant, then changed to inverted hysteresis with a higher Gu‐dopant. The hysteresis tunability behavior is attributed to the interplay of charge/ion accumulation and recombination at interfaces in the PSC. Furthermore, compared to the cell without Gu⁺‐dopant, the optimal content of 2% Gu⁺‐dopant also increases the device efficiency by 14%, reaching over 17% under one sun illumination.

F4‐TCNQ is applied to manipulate the morphological, electrical, and photovoltaic properties of nonfullerene solar cells. Adding a trace amount of F4‐TCNQ yields a higher current density and fill factor, in comparison to the reference device. The combined techniques evidence that the addition of F4‐TCNQ increases charge lifetime, charge mobility, and mean‐square composition variation.

Abstract

Fluorinated molecule 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4‐TCNQ) and its derivatives have been used in polymer:fullerene solar cells primarily as a dopant to optimize the electrical properties and device performance. However, the underlying mechanism and generality of how F4‐TCNQ affects device operation and possibly the morphology is poorly understood, particularly for emerging nonfullerene organic solar cells. In this work, the influence of F4‐TCNQ on the blend film morphology and photovoltaic performance of nonfullerene solar cells processed by a single halogen‐free solvent is systematically investigated using a set of morphological and electrical characterizations. In solar cells with a high‐performance polymer:small molecule blend FTAZ:IT‐M, F4‐TCNQ has a negligibly small effect on the molecular packing and surface characteristics, while it clearly affects the electronic properties and mean‐square composition variation of the bulk. In comparison to the control devices with an average power conversion efficiency (PCE) of 11.8%, inclusion of a trace amount of F4‐TCNQ in the active layer has improved device fill factor and current density, which has resulted into a PCE of 12.4%. Further increase in F4‐TCNQ content degrades device performance. This investigation aims at delineating the precise role of F4‐TCNQ in nonfullerene bulk heterojunction films, and thereby establishing a facile approach to fabricate highly optimized nonfullerene solar cells.

Next‐generation solar cells consisting of organic materials are studied. To develop novel dyes for dye‐sensitized solar cells, the essential dye structures are explored to attain high efficiency. Additionally, the interfaces in the perovskite solar cells are characterized via electrochemical methods, and newly developed laser deposition methods for perovskite layers are discussed.

Abstract

Next‐generation organic solar cells such as dye‐sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) are studied at the National Institute of Advanced Industrial Science and Technology (AIST), and their materials, electronic properties, and fabrication processes are investigated. To enhance the performance of DSSCs, the basic structure of an electron donor, π‐electron linker, and electron acceptor, i.e., D–π–A, is suggested. In addition, special organic dyes containing coumarin, carbazole, and triphenylamine electron donor groups are synthesized to find an effective dye structure that avoids charge recombination at electrode surfaces. Meanwhile, PSCs are manufactured using both a coating method and a laser deposition technique. The results of interfacial studies demonstrate that the level of the conduction band edge (CBE) of a compact TiO₂ layer is shifted after TiCl₄ treatment, which strongly affects the solar cell performance. Furthermore, a special laser deposition system is developed for the fabrication of the perovskite layers of PSCs, which facilitates the control over the deposition rate of methyl ammonium iodide used as their precursor.

Current cost drivers and potential avenues to reduce cost for organic solar modules by constructing a comprehensive bottom‐up cost model are examined. Moreover, the impact on the cost of alternative materials and constructions, process throughputs, module efficiency, and module lifetime, etc. is presented, and avenues for the further reduction of the minimum sustainable price and levelized cost of energy values are discussed.

Abstract

Organic photovoltaics (OPVs) have become a potential candidate for clean and renewable photovoltaic productions. This work examines the current cost drivers and potential avenues to reduce costs for organic solar modules by constructing a comprehensive bottom‐up cost model. The direct manufacturing cost (MC) and the minimum sustainable price (MSP) for an opaque single solar module (SSM) (MC = 187 ¥ m⁻², MSP = 297 ¥ m⁻²) and for a tandem solar module (MC = 224 ¥ m⁻², MSP = 438 ¥ m⁻²) are analyzed in detail. Within this calculation, the most expensive layers and processing steps are identified and highlighted. Importantly, the low levelized cost of energy (LCOE) value for an SSM with a 10% power conversion efficiency in a 20‐year range from 0.185 to 0.486 ¥ kWh⁻¹, with a national average of 0.324 ¥ kWh⁻¹ in China under an average solar irradiance of 1200 kWh m⁻² year⁻¹. Moreover, the impact on the cost of alternative materials and constructions, process throughputs, module efficiency, and module lifetime, etc., is presented and avenues to further reduce the MSP and LCOE values are indicated. The analysis shows that OPVs can emerge as a competitive alternative to established power generation technologies if the remaining issues (e.g., active layer material cost, module efficiency, and lifetime) can be resolved.

Trivalent cations (Sb³⁺ and In³⁺) can be spontaneously distributed with a gradient in organometal halide perovskites from homogeneous precursors, because of their difference in ionic size and electrostatic interaction between the dopants and the host atoms. This phenomenon can facilitate charge separation and collection of photoelectrons, leading to excellent photovoltaic performance.

Abstract

A gradient heterosturcture is one of the basic methods to control the charge flow in perovskite solar cells (PSCs). However, a classical route for gradient heterosturctures is based on the diffusion technique, in which the guest ions gradually diffuse into the films from a concentrated source of dopants. The gradient heterosturcture is only accessible to the top side, and may be time consuming and costly. Here, the “intolerant” n‐type heteroatoms (Sb³⁺, In³⁺) with mismatched cation sizes and charge states can spontaneously enrich two sides of perovskite thin films. The dopants at specific sides can be extracted by a typical hole‐transport layer. Theoretical calculations and experimental observations both indicate that the optimized charge management can be attributed to the tailored band structure and interfacial electronic hybridization, which promote charge separation and collection. The strategy enables the fabrication of PSCs with a spontaneous graded heterojunction showing high efficiency. A champion device based on Sb³⁺ doped film shows a stabilized power‐conversion efficiency of 21.04% with a high fill factor of 0.84 and small hysteresis.

Two novel A₁‐A₂ type polymer donors, PB24‐3TDC and PB68‐3TDC, with deep HOMO energy levels are proposed for non‐fullerene polymer solar cells. Slightly regulating the alkyl side‐chains causes a substantial difference in molecular stacking and photoluminescence emission energy loss, leading to broadly varied V _oc and J _sc. The best efficiency of 10.3% was achieved based on PB24‐3TDC:ITIC‐Th.

Introducing electron‐withdrawing groups onto donor‐acceptor (D‐A) type conjugated materials is a commonly used method for lowering their highest occupied molecular orbital (HOMO) energy level to achieve higher open circuit voltage (V _oc) in polymer solar cells (PSCs). However, this method is rather costly due to the tedious synthesis and low yield involved in preparing the target monomers. Here, a novel design concept of using two different acceptor units to construct acceptor₁‐acceptor₂ (A₁‐A₂) type polymers with a deep HOMO level is proposed. Two A₁‐A₂ type wide bandgap (WBG) polymers, PB24‐3TDC and PB68‐3TDC, were designed for PSCs. The developed polymers possess proper energy levels and complementary absorption with an efficient electron acceptor ITIC‐Th. More importantly, by slightly regulating the alkyl side‐chains, molecular stacking and photoluminescence (PL) emission energy loss of polymers can be alternated significantly. As a result, tuned V _oc from 0.9 to 1.0 V and short‐circuit current (J _sc) from 9.4 to 17.0 mA cm⁻² can be achieved. The device based on PB24‐3TDC:ITIC‐Th exhibits a higher power conversion efficiency (PCE) of 10.3% compared to PB68‐3TDC:ITIC‐Th based device with a PCE of 7.88%. These results show that the design concept of A₁‐A₂ type polymer donors have great potential for blending with non‐fullerene acceptors for achieving high performance PSCs.

A novel device structure of double‐side‐passivated perovskite solar cells is devised through intentionally distributing PbI₂ to both front/rear‐side surfaces and grain boundaries of perovskite film and a stabilized efficiency of 22% is achieved. Double‐side‐passivation effectively boosts the limits of open circuit voltage toward a record potential loss of 0.38 V for 1.53 eV‐bandgap perovskites.

An ideal crystal quality in the grain interior of perovskite polycrystalline films is well recognized; therefore, understanding interfacial impact and the ways to limit interfacial recombination is critical to fabricating highly efficient solar cells. In perovskite solar cells, PbI₂ has been used to passivate defects at grain boundaries, yet a systematic PbI₂ passivation engineering to boost the high‐performance perovskite solar cells has not been fully explored. Here, a novel device structure comprised of double‐side‐passivated perovskite solar cells (DSPC) is devised through intentionally distributing PbI₂ to both the front/rear‐side surfaces and grain boundaries of the formamidinium‐lead‐iodide‐based (FAPbI₃‐based) perovskite film. The minority carrier lifetime in double‐side‐passivated perovskite is extended to 1.1 μs with single‐exponential decay using time‐resolved photoluminescence. This result indicates a generic passivation effect of PbI₂ on perovskite interfaces, resembling SiO₂ passivation in silicon solar cells. Correspondingly, the best photovoltaic device with TiO₂‐based planar structure presents a stabilized efficiency of 22%. Moreover, DSPC effectively boosts the limits of open circuit voltages toward a record potential loss of 0.38 V for 1.53 eV‐bandgap perovskites. The architecture of double‐side‐passivated perovskite opens up new opportunities to exceed the efficiency of state‐of‐the‐art perovskite solar cells.

Melamine hydroiodide (MLAI) has been successfully introduced for preparing hetero structured MAPbI₃ perovskite for enhancing the photovoltaic performance and stability of perovskite solar cells in a robust humid ambient atmosphere (35 °C, 60–70% relative humidity). The power conversation efficiency of perovskite solar cells based on MLAI functionalized perovskite is 25% higher than that of pristine MAPbI₃ perovskite with nearly no hysteresis and high stability.

Despite the remarkable performance of organometallic halide perovskite solar cells (PSCs), their ultimate stability is still a major issue that inhibits the commercialization of this eminent technology. Herein, melamine hydroiodide (MLAI) is added to function methyl ammonium (CH3NH3⁺, MA⁺) lead iodide perovskite for fabricating structured perovskite with enhanced photovoltaic performance and stability in the harsh ambient atmosphere (35 °C, 60–70% relative humidity). Nearly no new phase formed even incorporated 25 mol.% MLAI induces the strain in the perovskite crystal structure. The MLAI‐structured perovskite film shows a denser and smoother surface than the pristine MAPbI₃ perovskite. Planar PSCs based on 2 mol.% MLAI‐functionalized perovskite show 17.2% power conversion efficiency with nearly no hysteresis which is much higher than pristine MAPbI₃ PSCs. Most importantly, the solar cell devices based on 2 mol.% MLAI‐functionalized perovskite still retain over 90% of the initial performance after being kept in ambient atmosphere for more than 560 h without encapsulation.

The energy level mismatch between a FA0.6MA0.4 Sn0.6Pb0.4I3 absorber and PEDOT:PSS based hole transporting layer are reduced and an improved V_OC over 50 mV and hence power conversion efficiencies of up to 15.85% are achieved.

Small bandgap Sn‐Pb mixed perovskite is generally regarded as the most promising structure to further enhance the power conversion efficiency of perovskite solar cells. However, the open circuit voltages (V _OCs) are usually lower than expected. In this work, by doping the generally used hole transporting layer (HTL) poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS) with a perfluorinated ionomer (PFI), we can tune the work function of it from −5.02 to −5.19 eV. This reduces the energy level mismatch between the FA_0.6MA_0.4 Sn_0.6Pb_0.4I₃ (FAMA) absorber and HTL, giving rise to enhanced built‐in voltage and better carrier extraction. The V _OC improves to over 50 mV, up to 0.783 V, resulting in an improved champion power conversion efficiency (PCE) of 15.85%. Moreover, the devices based on modified HTLs show improved stability at maximum power point. These results demonstrate that energy level tuning of the HTL is a promising strategy for the improvement of the PCEs of Sn‐Pb mixed inverted PSCs, and the addition of PFI is an effective method to tune the work function of PEDOT:PSS.

In article no. 1800167, Xinhua Li, Jianming Dai, Zhengguo Xiao, and co‐workers use an ultra‐thin Ti as a cathode interlayer, without using any organic or inorganic electron transport layers, to improve the efficiency of perovskite solar cells. Ti forms a bonding layer with nitrogen atoms in metylammonium anions at the perovskite/Ti interface, which passivates surface defects and suppresses surface decomposition of the perovskite film. A power conversion efficiency of 18.1% is achieved. Furthermore, Ti has low diffusivity and prevents the diffusion of the cathode metal atoms into the perovskite layer, resulting in improved device stability.

A high‐performance (12.9%) non‐fullerene organic solar cell processed using a sequential bilayer deposition method from non‐halogenated solvents is reported. Using this method, the organic solar cell can be scaled up to a larger area (1 cm²) while maintaining a high performance of 11.4% by doctor‐blade coating. This method offers a truly compatible processing technique for printing large area organic solar cell modules.

Abstract

While the performance of laboratory‐scale organic solar cells (OSCs) continues to grow over 13%, the development of high‐efficiency large area OSCs still lags. One big challenge is that the formation of bulk heterojunction morphology is an extremely complicated process and the formed morphology is also a highly delicate balance involving many parameters such as domain size, purity, miscibility, etc. The morphology control becomes much more challenging when the device area is scaled up. In this work, a highly efficient (12.9%) nonfullerene organic solar cell processed using a sequential bilayer deposition method from nonhalogenated solvents, is reported. Using this bilayer processing method, the organic solar cells can be scaled up to a larger area (1 cm²) while maintaining a high performance of 11.4% using doctor‐blade‐coating technique. Moreover, as the acceptor is hidden behind the polymer donor, the possibility of degradation by sunlight is lessened. Thus, improved photostability is observed in the bilayer structure device when compared with the bulk heterojunction device. This method offers a truly compatible processing technique for printing large‐area OSC modules.

The bulk and surface defects of perovskite films are suppressed by using SnO₂/TiO₂ double layer oxide, addition of methylammonium chloride (MACl) as a crystallization aid to the precursor solution, and surface passivation of perovskite films with iodine solution, due to the formation of high‐quality large‐grain perovskite films and retardation of radiationless carrier recombination.

Abstract

The presence of bulk and surface defects in perovskite light harvesting materials limits the overall efficiency of perovskite solar cells (PSCs). The formation of such defects is suppressed by adding methylammonium chloride (MACl) as a crystallization aid to the precursor solution to realize high‐quality, large‐grain triple A‐cation perovskite films and that are combined with judicious engineering of the perovskite interface with the electron and hole selective contact materials. A planar SnO₂/TiO₂ double layer oxide is introduced to ascertain fast electron extraction and the surface of the perovskite facing the hole conductor is treated with iodine dissolved in isopropanol to passivate surface trap states resulting in a retardation of radiationless carrier recombination. A maximum solar to electric power conversion efficiency (PCE) of 21.65% and open circuit photovoltage (V _oc) of ≈1.24 V with only ≈370 mV loss in potential with respect to the band gap are achieved, by applying these modifications. Additionally, the defect healing enhances the operational stability of the devices that retain 96%, 90%, and 85% of their initial PCE values after 500 h under continuously light illumination at 20, 50, and 65 °C, respectively, demonstrating one of the most stable planar PSCs reported so far.

In article number 1801892, Steve Albrecht, Vytautas Getautis and co‐workers demonstrate a novel promising concept for the formation of a hole selective monolayer in perovskite solar cells. A low temperature dopant‐free technique makes it suitable for different substrates.

By combining optical modeling and experimental results, the authors provide a full optical analysis for semitransparent organic solar cells (STOSCs). Defined as the sum of external quantum efficiency and transmittance, the term “quantum utilization efficiency (QUE)” is proposed as a parameter to describe light energy use in the semitransparent devices, which provides a new angle for analyzing STOSCs.

Semitransparent organic solar cells (STOSCs) show great potential for application as power generating windows for buildings. The power conversion efficiency (PCE) and the average visible transmittance (AVT) are both important parameters with which to evaluate the overall performance of STOSCs. However, it is very challenging to simultaneously improve these two performance parameters because they are intrinsically contradictory to each other. In this work, the optical and photovoltaic properties of STOSCs are investigated based on two model samples including PTB7‐Th:PC₆₁BM and PTB7‐Th:PC₇₁BM by systematically tuning their device structures. By combining optical modeling and experimental results, a full optical analysis is provided for the STOSCs with details on photon harvesting, optical losses, transmission properties, energy distribution spectrum, electric field intensity distribution, and photon absorption rate distribution within the devices. Defined as the sum of the external quantum efficiency and the transmittance, the term “quantum utilization efficiency” is used as a subjective parameter to describe the light energy use in the semitransparent devices, which provides an alternative angle for analyzing STOSCs.

Non‐peripheral octamethyl‐substituted copper (II) phthalocyanine nanowires are incorporated in poly(3‐hexylthiophene) to form nanocomposite, which exhibited higher hole mobilities and well‐matched energy levels. A power conversion efficiency of 16.61% is achieved for a perovskite solar cell based on composite hole‐transport material which retains 90% of their initial efficiencies after 800 h of storage at 25 °C with a relative humidity of 75% without any encapsulations.

New efficient hole‐transport material (HTM) composites based on low‐cost easy‐preparation non‐peripheral octamethyl‐substituted copper (II) phthalocyanine (N‐CuMe₂Pc) nanowire and poly(3‐hexylthiophene) (P3HT) are developed for CH₃NH₃PbI₃ (MAPbI₃)‐based perovskite solar cells (PSCs). Compared with pristine P3HT, the prepared nanocomposite HTMs provided thin films with better qualities and reduced trap densities, and exhibited higher hole mobilities and well‐matched energy levels with the perovskite layer. Depending on the ratio of the two components, the power conversion efficiency (PCE) reached up to 16.61%, which is higher than the efficiency of the standard device based on doped spiro‐OMeTAD (16.13%). Moreover, the long‐term stability of the PSCs is also improving greatly. The best performing devices based on P1C1 HTM retained 90% of their initial efficiencies after 800 h of storage with a relative humidity of 75%. These results indicate N‐CuMe₂Pc nanowire/P3HT nanocomposites can be an effective HTM to realize superior performance in PSCs.

Cellulose paper, as one of the four great inventions of China, possesses admirable properties like biocompatibility, biodegradability, and low cost and is a promising alternative to conventional substrates for perovskite solar cells (PSCs). In article no. 1800175, Bingqiang Cao, Jinghua Yu, and co‐workers fabricate a flexible holetransport‐ material‐free PSC with a power conversion efficiency of 9.05% on the cellulose paper, for the first time, which could be utilized in wearable electronics.

Publication date: 16 January 2019

Source: Joule, Volume 3, Issue 1

Author(s): Qian Kang, Long Ye, Bowei Xu, Cunbin An, Samuel J. Stuard, Shaoqing Zhang, Huifeng Yao, Harald Ade, Jianhui Hou

Context & Scale

Summary

Graphical Abstract