Chen Weijie

A combination strategy of using KBr modification and laser processing is demonstrated to prepare and optimize the SnO₂ film as the electron transport layer for rigid and flexible perovskite solar cells (PSCs). This strategy successfully improves the power conversion efficiency and durability of the rigid and flexible PSCs.

A combination of KBr modification and laser processing is utilized to prepare SnO₂ films for rigid and flexible perovskite solar cells (PSCs). The KBr modification effectively passivates the defects at the interface between SnO₂ and perovskite as well as grain boundaries of the perovskite film. A power conversion efficiency (PCE) of 20.14% is achieved with the KBr-modified SnO₂ for the rigid PSCs fabricated under a relative humidity of around 65–75%, compared to the pristine SnO₂ films with a PCE of 18.66%. Then, a picosecond ultraviolet laser is employed to process KBr-modified SnO₂ films on flexible substrates with a rapid scanning rate of 100 mm s⁻¹. The laser process improves the PCEs and durability of the PSCs. The flexible PSCs fabricated by the laser remain over 80% of their initial PCEs after 1000 bending cycles, higher than those fabricated by the hot plate showing 40% of their initial PCEs after the same bending cycles.

Aiming for high-efficiency solar cells with a low carbon footprint, we assess the quality of epitaxially grown p-type silicon wafers in terms of minority carrier lifetime, lifetime limitations, and solar cell efficiency potential. Epitaxially grown wafers with optimized base resistivity and thickness demonstrate an efficiency potential of 25.8% even after high-temperature treatment.

Combining the advantages of a high-efficiency solar cell concept and a low carbon footprint base material is a promising approach for highly efficient, sustainable, and cost-effective solar cells. In this work, we investigate the suitability of epitaxially grown p-type silicon wafers for solar cells with tunnel oxide passivating contact rear emitter. As a first proof of principle, an efficiency limiting bulk recombination analysis of epitaxially grown p-type silicon wafers deposited on high quality substrates (EpiRef) unveils promising cell efficiency potentials exceeding 25% for three different base resistivities of 3, 14, and 100 Ω cm. To understand the remaining limitations in detail, concentrations of metastable defects Fe _i , CrB and BO are assessed by lifetime-calibrated photoluminescence imaging and their impact on the overall recombination is evaluated. The EpiRef wafers’ efficiency potential is tracked along the solar cell fabrication process to quantify the impact of high temperature treatments on the material quality. We observe large areas with few structural defects on the wafer featuring lifetimes exceeding 10 ms and an efficiency potential of 25.8% even after exposing the wafer to a thermal oxidation at 1050 °C.

The industrialization of perovskite photovoltaics requires a scalable, fully automatic, low-cost, and high-throughput production method to fabricate the perovskite films. This review focuses on the scalable two-step fabrication of perovskite solar cells and modules. It highlights the advantage of vapor-based two-step deposition methods, promising to move perovskite photovoltaics toward commercialization.

Perovskite solar cells (PSCs) fabricated in laboratories have already achieved a power conversion efficiency (PCE) comparable to market-dominant crystalline silicon solar cells. However, this promising photovoltaic technology suffers from severe loss of PCE during scaling up, limiting its progress toward commercialization. One critical question is to develop scalable, low-cost, high throughput, and well-controlled production methods to deposit high-quality perovskite films. Among various approaches, two-step sequential deposition methods have their unique advantages but have been long overlooked. This review provides an overview of two-step methods for fabricating efficient and stable perovskite solar modules (PSMs). The mechanisms of two-step perovskite conversion and advanced engineering approaches to modulate the perovskite formation process are discussed first. The progress of efficient PSCs prepared by different two-step methods is surveyed and the advantages and disadvantages of each method for the scalable production of PSMs are compared. Particularly, it is highlighted that the vapor-based two-step methods are promising for high-throughput in-line production of PSMs. Finally, insights into the challenges and outlook of the industrialization of two-step processes for producing PSMs are provided.

Tetra-potassium hexacyanoferrate incorporation at the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/FASnI₃ interface increases PEDOT:PSS film conductivity, inhibits Sn²⁺ oxidation, and optimizes energy-level alignment. The champion device achieves an improved power conversion efficiency of 8.9% with superior long-term stability in a nitrogen atmosphere.

Sn-based perovskite material is one of the promising absorption materials due to its low toxicity and narrow bandgap. However, the unsatisfying quality of the perovskite film caused by Sn²⁺ oxidation and poor crystal growth greatly hinders the device performance. Herein, a layer of tetrapotassium hexacyanoferrate at the PEDOT:PSS/FASnI₃ interface is introduced, which can minimize the concentration of Sn⁴⁺, thereby suppressing the defect states in the perovskite film, enhancing the conductivity of the PEDOT:PSS film, and forming well-matched energy alignment in the device. Consequently, the champion device performance of 8.9% is obtained by the modified device, and the unencapsulated device can keep outstanding stability in N₂ atmosphere.

Interfacial engineering shows its merits in improving the performance of poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) based inverted perovskite solar cells, including engineering at PTAA/perovskite/electron transport layer (ETL), ETL/anode, and PTAA/perovskite interfaces, which can improve the wettability of PTAA, enhance the crystallinity of perovskite, hole extraction and charge transport, enhance film morphology and interface contact, optimize energy-level alignment, and restrain nonradiative recombination.

In recent years, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA)-based inverted perovskite solar cells (IPSCs) have gained tremendous attention due to their simple device structure, easy fabrication process, and suitability for roll-to-roll process for fabricating flexible devices. With the recent years’ rapid progress, PTAA-IPSCs have achieved higher efficiency than other IPSCs, revealing great potential for future applications. Among various strategies to enhance the performance of PTAA-IPSCs, interfacial engineering has been highlighted with comprehensive merits, including improving the wettability of PTAA, enhancing the crystallinity of perovskite, modifying energy levels, and reducing defect traps at interfaces for enhancing charge transfer and reducing nonradiative recombination. Although extensive review articles have been published on PSCs, little attention has been focused on interfacial engineering of PTAA-IPSCs. It is believed that it is of great importance to summarize the fruitful breakthroughs in recent years in this area and give some prospective. In this review, the development of PTAA-IPSCs is summarized, and then interfacial engineering processes on perovskite, PTAA, and electron transport layer is systematically discussed, respectively. In addition, current challenges associated with the rapid developments in the field of PTAA-IPSC have been pointed out and insightful outlooks for the future design and commercial development of PTAA-IPSCs have been provided.

The formate effectively suppressed oxidation through the coordinate bond to Sn. According to the density functional theory calculation, the formate interferes with the hydrogen bonding of FA⁺ and O₂, and the adsorption affinity is reduced. Comprising enhanced morphology with pinhole free, and a decrease of nonradiative recombination and trap density of perovskite film, the high-efficiency Pb-free FASnI₃ perovskite solar cells are successfully fabricated.

Pb-free Sn-based perovskite solar cells (PSCs) have significant potential for application in photovoltaic devices because of their suitable bandgap, low exciton binding energy, high carrier mobility, and long diffusion length. However, their performance is hampered by several issues. Sn-based perovskites are highly susceptible to oxidation, which induces a high concentration of defects and degrades the chemical stability of the perovskite crystals. Herein, the anion formate (HCOO ⁻ ) can effectively suppress the oxidation of Sn in the pure formamidinium tin triiodide (FASnI₃) perovskite without using A-site cationic additives. Moreover, the presence of formate results in a uniform pinhole-free perovskite film with a low trap density, reduced charge carrier recombination, and improved charge extraction. Density functional theory calculations show that formate-treated FASnI₃ has improved stability against oxidative Sn degradation. The formate-treated PSC achieves a power conversion efficiency of 12.11% at a high open-circuit voltage of 0.71 V. The device exhibits improved stability in ambient air in which it maintained over 80% of its initial power conversion efficiency after 180 min because oxidation is inhibited owing to the strong interaction between Sn and formate.

2,2′,7,7′-tetrakis(N,N-di(4-methoxyphenyl)amino)-9,9-spirobifluorene (Spiro-OMeTAD) has been widely applied as an efficient hole transport layer for perovskite solar cells but the issues related to device stability need to be addressed. Here, recent advances in Spiro-OMeTAD engineering toward improved device stability have been summarized from the perspective of the optimization strategies. Remaining challenges, as well as opportunities for future research are also discussed.

Abstract

Perovskite solar cells (PSCs) have undergone unprecedented growth in the past decade as an emerging photovoltaic technology. Up till now, the power conversion efficiency of PSCs has exceeded 25% that rivals silicon solar cells and there is still room for further enhancement. However, the development in long-term stability lags far behind, which remains a great concern for the commercial application in the future. The device instability mainly arises from the functional components, including perovskite film, charge transport layers, and electrodes along with the involved interfaces. As the most widely studied hole transport layer at the current stage, 2,2′,7,7′-tetrakis(N,N-di(4-methoxyphenyl)amino)-9,9-spirobifluorene (Spiro-OMeTAD) helps contribute to the achievement of record efficiency but it weakens the device stability due to the doping-induced side effects such as hygroscopicity and ion migration. Great efforts are devoted to boosting the stability of Spiro-OMeTAD while maintaining excellent photovoltaic performance. In this review, the fundamental properties of Spiro-OMeTAD have been summarized and the recent advances in engineering Spiro-OMeTAD-based hole transport layer for the sake of highly efficient PSCs with enhanced longevity are highlighted. In the end, an outlook for the further optimization of Spiro-OMeTAD is provided and the issues related to large-scale production are discussed.

Copper(II) 2,3,9,10,16,17,23,24-octakis((4-(bis(4-methoxyphenyl)amino)phenyl)ethynyl)phthalocyanine (8TPAEPC) with high-carrier mobility of 3.12 × 10⁻³ cm² V⁻¹ s⁻¹ is synthesized to extend the photovoltaic response of perovskite to 850 nm. The target perovskite solar cells (PSCs9 are qualified with increased power conversion efficiency (PCE) from 20% to 22.10%. Meanwhile, PCE of the PSCs with 8TPAEPC dopant-free hole transport layer (HTL) reaches 20.42%, which reaches state of the art level among the dopant-free metal phthalocyanines HTL-based PSCs.

Abstract

The absent photo-response in near-infrared (NIR) light (>800 nm) of lead-based perovskite solar cells (PSCs) limits the further improvement of their power conversion efficiency (PCE). Here, a narrow bandgap p-type phthalocyanine derivative (Copper(II) 2,3,9,10,16,17,23,24-octakis((4-(bis(4-methoxyphenyl)amino)phenyl)ethynyl)phthalocyanine –8TPAEPC) with NIR absorption is synthesized to extend the photovoltaic response of perovskite to 850 nm. After doping the 8TPAEPC into the perovskite photoactive layer, the perovskite crystal quality is improved, resulting in its good electrical conductivity and less surface defects. Furthermore, the molecules stacking on the grain boundaries construct the charge transportation paths, as well as the p–n bulk heterojunction with enhanced built-in potential. The target PSCs are optimized with notably enhanced PCE from 20% up to 22.10%, and excellent stability that is over 80% of the initial level at 70–80% relative humidity can be maintained for more than 500 h, benefiting from the improved hydrophobicity of 8TPAEPC. In addition, 8TPAEPC also serves as a dopant-free, highly carrier-mobile, and moreover, NIR-responsive hole transport layer (HTL) with boosted PCE of 20.42% that reaches state of the art level among the dopant-free metal phthalocyanines HTL-based PSCs.

A thiourea competitive crystallization strategy is proposed to manipulate the nonequilibrium nucleation and growth in solution processible perovskite materials. The embedding thiourea has succeeded in passivating the defects, healing the lattice mismatch and relaxing the residual tensile stress. The optimized device achieves the champion efficiency over 24% simultaneously with excellent storage and illumination stabilities.

Abstract

The solution process of perovskite solar cells may lead to widespread defects in the device, causing severe nonradiative recombination and the loss of conversion efficiency. Herein, a strategy of embedding thiourea into perovskite to manipulate the crystallization process and passivate the defects simultaneously is demonstrated. A competitive crystallization mechanism by embedding thiourea into perovskite has been proposed for the improvement of morphology and crystallinity. The defects in the device have been dramatically decreased by the strong coordination of CS bond in thiourea with the undercoordinated Pb²⁺. Moreover, the bilateral affinity of thiourea to the SnO₂ and perovskite can enhance the interface contact by the bridging bonding, which will release the residual stress of perovskite films. As a result, the thiourea-embedding device achieves a power conversion efficiency over 24% and shows excellent storage and illumination stabilities. Even undergoing 3768 h storage, the maximum efficiency value of unencapsulated device keeps over 94%. Furthermore, the efficiency of the optimized device maintains over 80% after 120 h continuous illumination at 60 °C.

Engineering of donor–acceptor–donor functional enamine hole transporting materials is presented leading to the low-cost hole transporting materia V1359 to reach power conversion efficiency over 22% in perovskite solar cells with excellent stability surpassing the reference spiro-OMeTAD due to the incorporation of the malononitrile acceptor units that passivate the surficial perovskite defects via Pb–N interactions.

Abstract

In this study, a series of donor–acceptor–donor (D-A-D) type small molecules based on the fluorene and diphenylethenyl enamine units, which are distinguished by different acceptors, as holetransporting materials (HTMs) for perovskite solar cells is presented. The incorporation of the malononitrile acceptor units is found to be beneficial for not only carrier transportation but also defects passivation via Pb–N interactions. The highest power conversion efficiency of over 22% is achieved on cells based on V1359, which is higher than that of spiro-OMeTAD under identical conditions. This st shows that HTMs prepared via simplified synthetic routes are not only a low-cost alternative to spiro-OMeTAD but also outperform in efficiency and stability state-of-art materials obtained via expensive cross-coupling methods.

An amine salts vapor healing strategy is applied to simultaneously passivate the defects across the entire perovskite film and obstruct the interfacial redox reaction between NiO_x and perovskite, enhancing both the device performance and the performance consistency. The vapor healing strategy substantially reduces the trap density and promotes device power conversion efficiency from 17.92% to 20.48% with improved operational device stability.

Abstract

Post-treatment is a widely used strategy to reduce defects in perovskite films, but has been largely limited to the solution phase. Herein, the posttreatment tool kit and develop a universal amine salts (A^IX^I) vapor healing strategy by taking advantage of the penetrating power of vapor and the soft-matter characteristics of halide perovskite is expanded. In a striking demonstration, the post-treatment of pristine perovskite layers allows simultaneous filling of the MA⁺ and I^– vacancies, passivation of both the cation and anion defects, and healing of the films to high order and high crystallinity required for high device performance, from the surface to the bulk and all the way down to the bottom. Experiments and DFT calculations revealed that charge extraction can be enhanced and non-radiative recombination can be reduced by regulating the energy levels and reducing the trap states via the A^IX^I vapor healing. Moreover, the diffusing A^IX^I can reach the NiO_x surface to obstruct the undesirable interfacial reactions and passivate the interface defects, further reducing the open-circuit voltage (V _oc) loss. The vapor healing strategy substantially reduces the trap density from 4.76 × 10¹⁵ to 1.04 × 10¹⁵ cm^–3, and promots power conversion efficiency of the champion device from 17.92% to 20.48% with superior device consistency, V _oc up to 1.114 V and the operational device stability.

Methylthiotriphenylamine-substituted copper phthalocyanine (SMe-TPA-CuPc) is synthesized and used as dopant-free HTM for perovskite solar cells. Owing to the strong interaction between the -SMe and undercoordinated lead, SMe-TPA-CuPc molecules could diffuse into the perovskite film after thermal annealing and effectively passivate the defects in the bulk and at the interface, which led to high efficiency and thermally stable devices.

Abstract

Simultaneous passivation of the defects at the surface and grain boundaries of perovskite films is crucial to achieve efficient and stable perovskite solar cells (PSCs). It is highly desirable to accomplish the above passivation through rational engineering of hole transport materials (HTMs) in combination with appropriate procedure optimization. Here, methylthiotriphenylamine-substituted copper phthalocyanine (SMe-TPA-CuPc) is reported as a dopant-free HTM for PSCs, exhibiting excellent efficiency, and stability. After thermal annealing, SMe-TPA-CuPc molecules diffused into the bulk of the perovskite film and effectively passivated the defects in the bulk and at the interface of the perovskite, owing to the strong interaction between the methylthio moiety and undercoordinated lead. The best-performing annealed SMe-TPA-CuPc-based device shows efficiency of 21.51%, which is higher than the unannealed SMe-TPA-CuPc-based device (power-conversion efficiency (PCE) of 20.75%) and reference doped spiro-OMeTAD-based device (PCE of 20.61%). Further modification of the perovskite of the annealed SMe-TPA-CuPc-based device by the QAPyBF4 additive result in even higher efficiency of 23.0%. It also shows excellent stability, maintaining 96% of its initial efficiency after 3624 h aging at 85 °C. This work highlights the great potential of phthalocyanine-based dopant-free HTMs and the defect passivation by thermal-induced molecular diffusion strategy for developing highly efficient and stable PSCs.

The effects of sulphur atoms positions of dithienothiophene on electronic property of hole-transport materials and performances of perovskite solar cells are systematically investigated. The positional variation of sulphur atoms in dithienothiophene not only gradually improves electron delocalization and enhances hole mobility but also effectively suppresses nonradiative recombination of perovskite solar cells.

Abstract

Hole transport materials (HTMs) are of great significance to improve the efficiency and long-term stability of perovskite solar cells (PVSCs). Herein, a series of new HTMs based on isomeric dithienothiophene (DTT) are designed and synthesized. Effects of sulphur (S) atoms positions on defect passivation and performance of PVSCs are systematically investigated through theoretical computation, X-ray diffraction, X-ray photoelectron spectroscopy, etc. The three molecules display noticeable isomeric effect in energy level, light absorption, and hole mobility. With S atoms varied from bottom-bottom-bottom in 3T-1 to bottom-bottom-top in 3T-2, then to bottom-top-bottom in 3T-3, the grown perovskite crystallite on the corresponding HTMs shows more homeogenous film morphology and less pinhole traps. Meanwhile, nonradiative recombination losses can be suppressed and hole extraction efficiency at HTM/perovskite surface can be improved from 3T-1 to 3T-3. As a result, the remarkable improvement of short-circuit current density nd open-circuit voltage in inverted perovskite solar cells can be realized with increasing the sulphur atoms contribution to the molecular conjugation. More importantly, 3T-3-based dopant-free HTM achieves a top power conversion efficiency of 19.23% in PVSCs with good device stability under green solvent processing. These results demonstrate the role of S atoms positions in HTMs on photovoltaic performance of PVSCs and the potential of DTT in developing eco-friendly HTMs toward efficient PVSCs.

Mixed-halide perovskites offer ideal bandgaps for tandem solar cells, but photoinduced halide segregation compromises photovoltaic device performance. This study explores how the presence of a hole-transport layer influences such effects, by monitoring halide segregation through in situ, concurrent X-ray diffraction, and photoluminescence measurements to disentangle compositional and optoelectronic changes. In addition, selective trap passivation techniques are shown to influence halide segregation.

Abstract

Mixed-halide perovskites offer ideal bandgaps for tandem solar cells, but photoinduced halide segregation compromises photovoltaic device performance. This study explores the influence of a hole-transport layer, necessary for a full device, by monitoring halide segregation through in situ, concurrent X-ray diffraction and photoluminescence measurements to disentangle compositional and optoelectronic changes. This work demonstrates that top coating FA_0.83Cs_0.17Pb(Br_0.4I_0.6)₃ perovskite films with a poly(triaryl)amine (PTAA) hole-extraction layer surprisingly leads to suppression of halide segregation because photogenerated charge carriers are rapidly trapped at interfacial defects that do not drive halide segregation. However, the generation of iodide-enriched regions near the perovskite/PTAA interface enhances hole back-transfer from the PTAA layer through improved energy level offsets, increasing radiative recombination losses. It is further found that while passivation with a piperidinium salt slows halide segregation in perovskite films, the addition of a PTAA top-coating accelerates such effects, elucidating the specific nature of trap types that are able to drive the halide segregation process. This work highlights the importance of selective passivation techniques for achieving efficient and stable wide-bandgap perovskite photovoltaic devices.

1H-benzimidazole as a dual-site passivator is introduced into perovskite precursors, achieving uniform and compact perovskite films with reducing defects, inhibiting ion migration. Simultaneously, the optimized band alignment promotes the separation of electrons and holes. Consequently, the target perovskite solar cell devices show not only improved efficiency but also remarkable stability. Moreover, density functional theory calculations provide insight into the passivation mechanism.

Abstract

Defect passivation has been recognized as an effective strategy to improve efficiency and stability of perovskite solar cells (PSCs). In this work, in-depth theoretical calculations and experimental characterizations reveal the dual-site synergistic passivation of 1H-benzimidazole (BIZ), and the conjugated structure of the benzene ring tends to increase the interaction between BIZ and perovskite. High-quality perovskite films are thus achieved, with increased grain size, reduced defect density, and suppressed ion migration. Simultaneously, the reduced work function and optimized band alignment promote carrier transport, reducing nonradiative recombination, and loss of open-circuit voltages, as well as fill factor. Consequently, the target PSC devices achieve a champion power conversion efficiency (PCE) of 24.59%, and 20.49% for perovskite solar module (a designated area of 27.5 cm²). The unencapsulated PSC maintains 91.49% of original PCE after storing in air with an average relative humidity of 40% for 2400 h. Moreover, the device exhibits remarkable the long-term operational stability, maintaining 90.47% of initial PCE after continuously operating at the maximum power point for 1000 h. This study not only provides insights into the synergistic passivation of BIZ but also provides a strategy for the application of BIZ derivatives in the photovoltaic field.

Three polymer analogues to polyaniline (PANI), PANI–carbazole (P1), PANI–phenoxazine (P2), and PANI–phenothiazine (P3) are designed with different energy levels to modify the interface between poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) and the MAPbI₃-based perovskite layer and improve the device performance. The order of contribution for the three effects of the polymer modification is work function adjustment > surface modification > perovskite growth control.

Abstract

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is a popular hole transport material in perovskite solar cells (PSCs). However, the devices with PEDOT:PSS exhibit large open-circuit voltage (V _oc) loss and low efficiency, which is attributed to mismatched energy level alignment and the poor interface of PEDOT:PSS and perovskite. Here, three polymer analogues to polyaniline (PANI), PANI–carbazole (P1), PANI–phenoxazine (P2), and PANI–phenothiazine (P3) are designed with different energy levels to modify the interface between PEDOT:PSS and the perovskite layer and improve the device performance. The effects of the polymers on the device performance are demonstrated by evaluating the work function adjustment, perovskite growth control, and interface modification in MAPbI₃-based PSCs. Low bandgap Sn–Pb-based PSCs are also fabricated to confirm the effects of the polymers. Three effects are evaluated through the comparison study of PEDOT:PSS-based organic solar cells and MAPbI₃ PSCs based on the PEDOT:PSS modified by P1, P2, and P3. The order of contribution for the three effects is work function adjustment > surface modification > perovskite growth control. MAPbI₃ PSCs modified with P2 exhibit a high V _oc of 1.13 V and a high-power conversion efficiency of 21.06%. This work provides the fundamental understanding of the interface passivation effects for PEDOT:PSS-based optoelectronic devices.

A high-performance and self-powered blue perovskite photodetector (PPD) is developed by designing and optimizing A-site of APb(Br_0.65Cl_0.35)₃ (A = formamidinium (FA⁺), methylammonium (MA⁺), Cs⁺) perovskites (PVSKs). The incorporation of Cs⁺ into FA/MA-PVSKs reduces the lattice strain and defect density. Consequently, a best-performing Cs-incorporating device shows an external quantum efficiency (EQE) of 84.9% which is the highest EQE reported in blue PDs.

Abstract

A self-powered, color-filter-free blue photodetector (PD) based on halide perovskites is reported. A high external quantum efficiency (EQE) of 84.9%, which is the highest reported EQE in blue PDs, is achieved by engineering the A-site monovalent cations of wide-bandgap perovskites. The optimized composition of formamidinium (FA)/methylammonium (MA) increases the heat of formation, yielding a uniform and smooth film. The incorporation of Cs⁺ ions into the FA/MA composition suppresses the trap density and increases charge-carrier mobility, yielding the highest average EQE of 77.4%, responsivity of 0.280 A W⁻¹, and detectivity of 5.08 × 10¹² Jones under blue light. Furthermore, Cs⁺ improves durability under repetitive operations and ambient atmosphere. The proposed device exhibits peak responsivity of 0.307 A W⁻¹, which is higher than that of the commercial InGaN-based blue PD (0.289 A W⁻¹). This study will promote the development of next-generation image sensors with vertically stacked perovskite PDs.

Organic additive engineering is demonstrated to be an effective strategy for improving the perovskite crystallization and reducing the perovskite defects. The progresses on organic additive engineering to grow high-quality inorganic CsPbX₃ perovskites by dividing organic additives into two categories are discussed.

Inorganic CsPbX₃ (X: Br, I, or their mixture) perovskite solar cells have gained widespread attention due to their superior stability and the steadily increased conversion efficiency. Inorganic CsPbX₃ perovskite for solar cell application are usually fabricated by the solution-processing method. The nature of solution-processing method and the rapid crystal growth of perovskite lead to the formation of a wide range of defects within CsPbX₃ perovskite films, which deteriorate the performance and stability of CsPbX₃ devices. Recently, organic additive engineering has been demonstrated to be an effective strategy for improving the perovskite quality. Herein, the recent progress of organic additive engineering to grow high-quality inorganic CsPbX₃ perovskite films for high-performance solar cells is summarized. The role of organic additives in the formation of inorganic CsPbX₃ perovskite films and their effect on the performance of corresponding perovskite solar cells are discussed. In addition, some issues of organic additive engineering that should be deeply understood are summarized, and the research trend on organic additive engineering for further improving the performance of CsPbX₃ devices is suggested.

Here, an effective strategy is presented for inhibiting the growth of 1D solvate intermediates during the fabrication process of quasi-2D Ruddlesden−Popper perovskite solar cells, through introducing guanidinium thiocyanate inhibitor in precursor solution. The device power conversion efficiency and stability are significantly improved with reduced trap densities and enhanced carrier mobilities.

Abstract

Quasi-2D perovskite solar cells have recently emerged as a highly prospective and inexpensive solution for sustainable energy due to their intrinsic optoelectronic properties and stability. The qualities of these promising quasi-2D perovskite cells are generally affected by different intermediates derived from the precursor solution during film fabrication processing. However, efficient solutions to inhibit intermediates remain insufficient to date. Here, an effective strategy is prsented to inhibit the growth of 1D solvate intermediate during the fabricating process of quasi-2D perovskite films by introducing a guanidinium thiocyanate (GUASCN) inhibitor. Theoretical calculations reveal that the SCN⁻ anions spontaneously replace the iodide ions in the inorganic framework [PbI₆]³⁻ and induce the decomposition of the solvate intermediate. The resulted perovskite solar cells exhibit a significant improvement in power conversion efficiency (PCE), benefiting from the reduced trap-state density and enhanced carrier mobilities. The unencapsulated devices retain 91% and 95% of the original PCEs under 45 ± 10% humidity in air or under continuous light irradiation at 100 mW cm⁻² and 45 °C in a nitrogen atmosphere for 1000 h. Particularly, devices without electron-transporting layers maintain 85% of the peak PCE under maximum power point tracking at 45 °C for 1000 h.

High quality colloidal ZnO quantum dots (ZnO OM) are synthesized using a new wet-organometallic approach. The use of ZnO OM as an electron transfer layer (ETL) in planar perovskite solar cells improves the ETL/perovskite interface stability and reduces charge carrier recombination pathways. Consequently, the performance and stability of the ZnO OM-based device is improved compared to the control device fabricated on the sol–gel processed ZnO ETL.

Abstract

Zinc oxide (ZnO) is a promising electron-transport layer (ETL) in thin-film photovoltaics. However, the poor chemical compatibility between commonly used sol–gel-derived ZnO nanostructures and organo–metal halide perovskites makes it highly challenging to obtain efficient and stable perovskite solar cells (PSCs). Here, a novel approach is reported for low-temperature processed pure ZnO ETLs for planar heterojunction PSCs based on ZnO quantum dots (QDs) stabilized by dimethyl sulfoxide (DMSO) as easily removable solvent molecules. With no need for the ETL doping or surface modification, the champion PSC comprising the mixed-cation and mixed-halide Cs₅(MA_0.17FA_0.83)₉₅Pb(I_0.83Br_0.17)₃ absorber layer reaches a maximum power conversion efficiency of 20.05%, which is significantly higher than that obtained for a reference device based on a standard sol–gel-derived ZnO nanostructured layer (17.78%). Thus, along with the observed better operational stability in ambient conditions and elevated temperature, the champion device achieves the state-of-the-art performance among reported non-passivated pure ZnO ETL-based PSCs. The improved photovoltaic performance is attributed to both a higher uniformity of the surface morphology and a lower defects density of films based on the organometallic-derived QDs that are likely to ensure the enhanced stability of the ZnO/perovskite interface.

By employing a holistic optimization strategy to reduce the V _OC-deficit of the 1.77 eV wide-bandgap perovskite solar cells, the first proof-of-concept four-terminal all-perovskite flexible tandem solar cell with a power conversion efficiency of 22.6% is presented. When integrating into two-terminal flexible tandems, 23.8% flexible all-perovskite tandem solar cells with a superior V _OC of 2.1 V are achieved.

Abstract

Among various types of perovskite-based tandem solar cells (TSCs), all-perovskite TSCs are of particular attractiveness for building- and vehicle-integrated photovoltaics, or space energy areas as they can be fabricated on flexible and lightweight substrates with a very high power-to-weight ratio. However, the efficiency of flexible all-perovskite tandems is lagging far behind their rigid counterparts primarily due to the challenges in developing efficient wide-bandgap (WBG) perovskite solar cells on the flexible substrates as well as their low open-circuit voltage (V _OC). Here, it is reported that the use of self-assembled monolayers as hole-selective contact effectively suppresses the interfacial recombination and allows the subsequent uniform growth of a 1.77 eV WBG perovskite with superior optoelectronic quality. In addition, a postdeposition treatment with 2-thiopheneethylammonium chloride is employed to further suppress the bulk and interfacial recombination, boosting the V _OC of the WBG top cell to 1.29 V. Based on this, the first proof-of-concept four-terminal all-perovskite flexible TSC with a power conversion efficiency of 22.6% is presented. When integrating into two-terminal flexible tandems, 23.8% flexible all-perovskite TSCs with a superior V _OC of 2.1 V is achieved, which is on par with the V _OC reported on the 28% all-perovskite tandems grown on the rigid substrate.

The conventional hole-extracting polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate in organic bulk-heterojunction (BHJ) photovoltaics is replaced with engineered self-assembled monolayers (SAMs). Combining the nanometre-thin SAM interlayers with an n-doped BHJ, organic photovoltaics with improved stability and a maximum power conversion efficiency of 18.9% are demonstrated.

Abstract

The influence of halogen substitutions (F, Cl, Br, and I) on the energy levels of the self-assembled hole-extracting molecule [2-(9H-Carbazol-9-yl)ethyl]phosphonic acid (2PACz), is investigated. It is found that the formation of self-assembled monolayers (SAMs) of [2-(3,6-Difluoro-9H-carbazol-9-yl)ethyl]phosphonic acid (F-2PACz), [2-(3,6-Dichloro-9H-carbazol-9-yl)ethyl]phosphonic acid (Cl-2PACz), [2-(3,6-Dibromo-9H-carbazol-9-yl)ethyl]phosphonic acid (Br-2PACz), and [2-(3,6-Diiodo-9H-carbazol-9-yl)ethyl]phosphonic acid (I-2PACz) directly on indium tin oxide (ITO) increases its work function from 4.73 eV to 5.68, 5.77, 5.82, and 5.73 eV, respectively. Combining these ITO/SAM electrodes with the ternary bulk-heterojunction (BHJ) system PM6:PM7-Si:BTP-eC9 yields organic photovoltaic (OPV) cells with power conversion efficiency (PCE) in the range of 17.7%–18.5%. OPVs featuring Cl-2PACz SAMs yield the highest PCE of 18.5%, compared to cells with F-2PACz (17.7%), Br-2PACz (18.0%), or I-2PACz (18.2%). Data analysis reveals that the enhanced performance of Cl-2PACz-based OPVs relates to the increased hole mobility, decreased interface resistance, reduced carrier recombination, and longer carrier lifetime. Furthermore, OPVs featuring Cl-2PACz show enhanced stability under continuous illumination compared to ITO/PEDOT:PSS-based cells. Remarkably, the introduction of the n-dopant benzyl viologen into the BHJ further boosted the PCE of the ITO/Cl-2PACz cells to a maximum value of 18.9%, a record-breaking value for SAM-based OPVs and on par with the best-performing OPVs reported to date.

Highly stable and efficient lead-free tin-perovskite solar cells have been fabricated utilizing composites such as Sn-perovskite:N _x GO in the active layer, PEDOT:PSS-N _x GO in the hole transport layer, and Al₂O₃-N _x GO in the interfacial layer. The champion device shows remarkable efficiency of 13.25%, light stability with retaining 95% of the initial values of photovoltaic parameters over 60 min illumination, long-term stability sustaining ≈91% of initial efficiency over 60 d in Ar atmosphere.

Abstract

Tin-based perovskite (Sn-PS) is one of the most promising candidates in lead-free perovskite solar cells (PSCs), but its poor stability and low power conversion efficiency (PCE) have been the main bottleneck towards further development. Here, to develop a stable and efficient Sn-based PSC, nitrogen-doped graphene oxide (N _x GO) has been, for the first time, incorporated in active, hole-transport and interfacial layers. The inclusion of N _x GO slowed the crystallization of Sn-PS and suppressed the Sn²⁺/Sn⁴⁺ oxidation, resulting in pinhole-free dense films having large grains, reduction of recombination loss, well-matched energy levels, and thereby significantly improving the device performance. Compared to the pristine Sn-PS cells, the champion devices with N _x GO-based composites in active, hole-transport, and interfacial layers showed dramatic enhancement of photovoltaic parameters (i.e., open-circuit voltage = 0.961 V, photocurrent = 21.21 mA cm⁻², fill factor = 65.05% and PCE = 13.26%). Furthermore, the N _x GO-based cells without encapsulation showed remarkable improvement of long-term stability with sustaining 91% of the initial PCE over 60 d, photostability, and reproducibility.

The 10H,10′H-9,9′-spirobi[acridine] core including moieties featuring two non-equivalent N-substituted-9,10-dihydroacridine subunits with different structural and electronic characteristics were designed as HTMs of PSCs. The planar 3,6-dimethoxy-9H-carbazole units based HTM (BSA50) not only exhibits better electronic properties, but also results in better passivating capability for the perovskite trap states via stronger donor ability.

Abstract

Hole-transporting materials (HTMs) based on the 10H, 10′H-9,9′-spirobi [acridine] core (BSA50 and BSA51) were synthesized, and their electronic properties were explored. Experimental and theoretical studies show that the presence of rigid 3,6-dimethoxy-9H-carbazole moieties in BSA 50 brings about improved hole mobility and higher work function compared to bis(4-methoxyphenyl)amine units in BSA51, which increase interfacial hole transportation from perovskite to HTM. As a result, perovskite solar cells (PSCs) based on BSA50 boost power conversion efficiency (PCE) to 22.65 %, and a PSC module using BSA50 HTM exhibits a PCE of 21.35 % (6.5×7 cm) with a V _oc of 8.761 V and FF of 79.1 %. The unencapsulated PSCs exhibit superior stability to devices employing spiro-OMeTAD, retaining nearly 90 % of their initial efficiency after 1000 h operation output. This work demonstrates the high potential of molecularly engineered spirobi[acridine] derivatives as HTMs as replacements for spiro-OMeTAD.

Nature Energy, Published online: 06 October 2022; doi:10.1038/s41560-022-01132-4