Accelerated Sequential Deposition Reaction via Crystal Orientation Engineering for Low-Temperature,High-Efficiency Carbon-Electrode CsPbBr_(3) Solar Cells

Low-temperature,ambient processing of high-quality CsPbBr_(3)films is demanded for scalable production of efficient,low-cost carbon-electrode perovskite solar cells(PSCs).Herein,we demonstrate a crystal orientation engineering strategy of PbBr_(2)precursor film to accelerate its reaction with CsBr precursor during two-step sequential deposition of CsPbBr_(3)films.Such a novel strategy is proceeded by adding CsBr species into PbBr_(2)precursor,which can tailor the preferred crystal orientation of PbBr_(2)film from[020]into[031],with CsBr additive staying in the film as CsPb_(2)Br_(5)phase.Theoretical calculations show that the reaction energy barrier of(031)planes of PbBr_(2)with CsBr is lower about 2.28 eV than that of(O2O)planes.Therefore,CsPbBr_(3)films with full coverage,high purity,high crystallinity,micro-sized grains can be obtained at a low temperature of 150℃.Carbon-electrode PSCs with these desired CsPbBr_(3)films yield the record-high efficiency of 10.27%coupled with excellent operation stability.Meanwhile,the 1 cm^(2)area one with the superior efficiency of 8.00%as well as the flexible one with the champion efficiency of 8.27%and excellent mechanical bending characteristics are also achieved.

Optimization of solvent swelling for efficient organic solar cells via sequential deposition

Compared to bulk heterojunction(BHJ)organic solar cells(OSCs)prepared by the blend casting in“one step process”,sequential deposition(SD)processed OSCs can realize an ideal profile of vertical component distribution due to the swelling of polymer films.Herein,we did trials on several kinds of second solvents for swelling the polymer layer,and investigated the packing structure and morphology of the swollen films and the performance of the resulting devices.We found that an optimized morphology can be achieved by solvent swelling while using orthodichlorobenzene(o-DCB)as the second layer processing-solvent,with polymer donor PffBT-3 as bottom layer,PC71BM as top layer and bicontinuous networks in the middle.Such solvent swelling process also makes the SD method exempt from thermal annealing treatment.The device based on SD yields a power conversion effi-ciency(PCE)up to 8.7%without any post-treatment,outperforming those from the devices based on SD using other solvents and that(7.06%)from BHJ device,respectively.We also extended the use of this approach to allpolymer blend system,and successfully improved the efficiency from 4.72%(chloroform)to 9.35%(o-DCB),which is among the highest PCEs in all-polymer-based OSCs fabricated with SD method.The results demonstrate that the swelling of the polymer by the second layer solvent is a necessity for SD,paving the way towards additivefree high-performance OSCs.

Intermediate phase assisted sequential deposition of reverse-graded quasi-2D alternating cation perovskites for MA-free perovskite solar cells

One-step deposition approaches have been widely applied and developed in the fabrication of quasi-2D perovskites.However,the regulation of quantum wells(QWs)and crystalline orientation is difficult and complicated when using this methodology.Sequential deposition is another widespread synthetic approach for preparing perovskite films and perovskite dimension engineering.In this article,δ-CsPbI_(3)intermediate phase assisted sequential(IPAS)deposition is successfully carried out to fabricate MA-free quasi-2D ACI perovskites.The amount of theδ-CsPbI_(3)intermediate phase in the PbI2 layer and the concentration of GAI molecule in the IPA solution both play important roles in the production of MA-free quasi-2D ACI perovskite films.The n value of the MA-free quasi-2D ACI perovskites can be adjusted,which affects the photovoltaic performance and device stability.Compared with one-step deposition,the MA-free quasi-2D ACI perovskites prepared via IPAS deposition have opposite reverse-graded QW distribution and improved vertical orientation,leading to a remarkable PEC of up to 18.86%and allowing the preparation of unpackaged devices with prominent working stability(80%,400 h).The underlying mechanism and crystallization pathway of IPAS deposition confirm that sequential deposition has unique superiority in regulating the QW distribution and crystalline orientation of quasi-2D perovskites.

Enhancement of vertical phase separation in sequentially deposited organic photovoltaics through the independent processing of additives

Herein,the impact of the independent control of processing additives on vertical phase separation in sequentially deposited (SD) organic photovoltaics (OPVs) and its subsequent effects on charge carrier kinetics at the electron donor-acceptor interface are investigated.The film morphology exhibits notable variations,significantly depending on the layer to which 1,8-diiodooctane (DIO) was applied.Grazing incidence wide-angle X-ray scattering analysis reveals distinctly separated donor/acceptor phases and vertical crystallinity details in SD films.Time-of-flight secondary ion mass spectrometry analysis is employed to obtain component distributions in diverse vertical phase structures of SD films depending on additive control.In addition,nanosecond transient absorption spectroscopy shows that DIO control significantly affects the dynamics of separated charges in SD films.In SD OPVs,DIO appears to act through distinct mechanisms with minimal restriction,depending on the applied layer.This study emphasizes the significance of morphological optimization in improving device performance and underscores the importance of independent additive control in the advancement of OPV technology.

Over 16% efficiency all-polymer solar cells by sequential deposition

All-polymer solar cells(all-PSCs) have received extensive attention due to their excellent mechanical robustness and performance stability. However, the power conversion efficiency(PCE) of all-PSCs still lags behind those of organic solar cells(OSCs)based on non-fullerene small molecule acceptors. Herein, we report highly efficient all-PSCs via sequential deposition(SD) with donor and acceptor layers coated sequentially to optimize the film microstructure. Compared with the bulk heterojunction(BHJ)all-PSCs, an optimized morphology with vertical component distribution was achieved for the SD-processed all-PSCs due to the synergistic effect of swelling of polymer films and using additive. Such strategy involves using chlorobenzene as the first layer processing-solvent for polymer donor, chloroform as the second processing-solvent for polymer acceptor with trace 1-chloronaphthalene, efficiently promoting exciton dissociation and charge extraction and reducing trap-assisted recombination.Consequently, over 16% all-PSCs fabricated via SD method was realized for the first time, which is much higher than that(15.2%) of its BHJ counterpart and also among the highest PCEs in all-PSCs. We have further demonstrated the generality of this approach in various all-polymer systems. This work indicates that the SD method can yield excellent all-PSCs and provides a facile approach to fabricating high-performance all-PSCs.

Optimizing the morphology of all-polymer solar cells for enhanced photovoltaic performance and thermal stability

Due to the complicated film formation kinetics, morphology control remains a major challenge for the development of efficient and stable all-polymer solar cells(all-PSCs). To overcome this obstacle, the sequential deposition method is used to fabricate the photoactive layers of all-PSCs comprising a polymer donor PTzBI-oF and a polymer acceptor PS1. The film morphology can be manipulated by incorporating amounts of a dibenzyl ether additive into the PS1 layer. Detailed morphology investigations by grazing incidence wide-angle X-ray scattering and a transmission electron microscope reveal that the combination merits of sequential deposition and DBE additive can render favorable crystalline properties as well as phase separation for PTzBI-oF:PS1 blends. Consequently, the optimized all-PSCs delivered an enhanced power conversion efficiency(PCE) of 15.21%along with improved carrier extraction and suppressed charge recombination. More importantly, the optimized all-PSCs remain over 90% of their initial PCEs under continuous thermal stress at 65 °C for over 500 h. This work validates that control over microstructure morphology via a sequential deposition process is a promising strategy for fabricating highly efficient and stable all-PSCs.

Solution sequential deposited organic photovoltaics:From morphology control to large-area modules

Organic optoelectronic materials enable cutting-edge,low-cost organic photodiodes,including organic solar cells(OSCs)for energy conversion and organic photodetectors(OPDs)for image sensors.The bulk heterojunction(BHJ)structure,derived by blending donor and acceptor materials in a single solution,has dominated in the construction of active layer,but its morphological evolution during film formation poses a great challenge for obtaining an ideal nanoscale morphology to maximize exciton dissociation and minimize nongeminate recom-bination.Solution sequential deposition(SSD)can deliver favorable p–i–n vertical component distribution with abundant donor/acceptor interfaces and relatively neat donor and acceptor phases near electrodes,making it highly promising for excellent device performance and long-term stability.Focusing on the p–i–n structure,this review provides a systematic retrospect on regulating this morphology in SSD by summarizing solvent selection and additive strategies.These methods have been successfully implemented to achieve well-defined morphology in ternary OSCs,all-polymer solar cells,and OPDs.To provide a practical perspective,comparative studies of device stability with BHJ and SSD film are also discussed,and we review influential progress in blade-coating techniques and large-area modules to shed light on industrial production.Finally,challenging issues are out-lined for further research toward eventual commercialization.

Key parameters of two typical intercalation reactions to prepare hybrid inorganic-organic perovskite films

A star hybrid inorganic-organic perovskite material selected as an outstanding absorbing layer in solar cells benefits from multiple preparation techniques and excellent photoelectric characteristics. Among numerous synthetic processes, uniform, compact, and multi-stack perovskite thin films can be manufactured using vacuum deposition. During sequential vacuum deposition, the penetration ability of the organic molecules cannot be effectively controlled. In addition, the rela- tionship between the thickness of the inorganic seeding layer and the organic molecule concentration for optimized devices using an evaporation-solution method is unclear. In this work, we prepared high-quality perovskite films by effectively con- trolling the penetration ability and chemical quantity of organic methyl ammonium iodide by monitoring the evaporation pressure and time. Thus, a device efficiency of over 15% was achieved with an all-vacuum prepared perovskite film. For the evaporation-solution method, we reacted different thicknesses of inorganic lead iodine with various concentrations of the organic molecule solution. The inorganic layer thickness and organic molecule concentration showed a linear relationship to achieve an optimum perovskite film, and an empirical formula was obtained. This work noted the key parameters of two intercalation reactions to prepare perovskite films, which paves a way to deliver a device that enables multi-layered structures, such as tandem solar cells.

Performance enhancement in organic solar cells and photodetectors enabled by donor phase optimization at the surface of hole transport layer

The domain purity,material crystallinity and distribution at the interface between the active layer and the transport layer have an important impact on the performance of organic solar cells(OSCs)and organic photodetectors(OPDs),while this focal issue has received less attention in previous studies.From this perspective,a new method to simultaneously enhance the performance of OSC and OPD is proposed,namely,using a sequential deposition method to first construct a compact stacking structure of dualdonor(D18-Cl:PTO2)eutectic in the donor layer,and then induce the ordered deposition of the acceptor(Y6).Compared with the conventional bulk heterojunction(BHJ),the active layer realized by this method not only improves the crystallinity and stacking order of the constituent material on the surface of the transport layer,but also regulates a good vertical distribution,which is conducive to improving the charge transport and extraction efficiency,reducing the leakage current,and enhancing the stability of the device.As a result,the OSC device based on the D18-Cl:PTO2/Y6 structure achieves a power conversion efficiency of up to 17.65%and good light-degradation stability,which is much better than that of BHJbased OSC(PCE of 16.37%).For the OPD,the dark current at reverse bias is reduced by more than an order of magnitude,and the maximum responsivity is improved to 0.52 A/W through the optimization of the donor phase at the interface.Moreover,the strategy does not require additional post-processing compared to the BHJ preparation,which reduces the device construction cost and process complexity,providing an effective way for developing high-performance organic optoelectronic devices.

Control of vertical phase separation in high performance non-fullerene organic solar cell by introducing oscillating stratification preprocessing

Non-fullerene organic solar cell(NFOSC)has attracted tremendous attention due to their great potential for commercial applications.To improve its power conversion efficiency(PCE),generally,sequential solution deposition(SSD)methods have been employed to construct the graded vertical phase separation(VPS)of the bulk-heterojunction(BHJ)active layer for efficient exciton separation and charge transition.However,a variety of orthogonal solvents used in the SSD may lead to the unpredicted change in the BHJ morphology and introduce additional defects inside the BHJ bulk thus complicate the fabrication process.Here,a simple oscillating stratification preprocessing(OSP)is developed to facilitate the formation of graded VPS among the BHJ layer.As a result,a significant improvement is obtained in PCE from 10.96%to 12.03%,which is the highest value reported among PBDB-T:ITIC based NFOSC.

Molecular dispersion enhances photovoltaic efficiency and thermal stability in quasi-bilayer organic solar cells

In comparison to widely adopted bulk heterojunction(BHJ)structures for organic solar cells(OSC),exploiting the sequential deposition to form planar heterojunction(PHJ)structures enables to realize the favorable vertical phase separation to facilitate charge extraction and reduce charge recombination in OSCs.However,effective tunings on the power conversion efficiency(PCE)in PHJ-OSCs are still restrained by the currently available methods.Based on a polymeric donor PBDBT-2 F(PBDBT=Poly[[4,8-bis[5-(2-ethylhexyl)-4-fluoro-2-thienyl]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl]-2,5-thiophenediyl[5,7-bis(2-ethylhexyl)-4,8-dioxo-4 H,8 H-benzo[1,2-c:4,5-c′]dithiophene-1,3-diyl]-2,5-thiophenediyl])and a non-fullerene(NF)acceptor Y6,we proposed a strategy to improve the properties of photovoltaic performances in PHJ-based OSCs through dilute dispersions of the PBDBT-2 F donor into the acceptor-dominant phase with the sequential film deposition.With the control of donor dispersions,the charge transport balance in the PHJ-OSCs is improved,leading to the expedited photocarrier sweep-out with reduced bimolecular charge recombination.As a result,a PCE of 15.4%is achieved in the PHJ-OSCs.Importantly,the PHJ solar cells with donor dispersions exhibit better thermal stability than corresponding BHJ devices,which is related to the better film morphology robustness and less affected charge sweep-out during the thermal aging.