awn

Pb source plays a critical role in determining the solution-processed perovskite film's crystallization, structural, and optoelectronic properties. This review comprehensively summarized the current understanding and advanced development of Pb source engineering in perovskite solar cells (PSCs), which is hoped to motivate more ideas toward further development of high-performing PSCs with controllable, sustainable, and large-scale production.

Organic–inorganic hybrid Pb halide perovskites have gained much attention as the most promising next generation photovoltaics, and the certificated power conversion efficiency of perovskite solar cells (PSCs) has recently reached 25.5%. For the typical solution-processed film, the features of solutes in the precursor solution greatly influence the characteristics of the deposited film. While for Pb-based perovskites, PbI₆ octahedral is the key component of the perovskite framework, and thus the Pb source particularly plays a significant role in determining the crystallization, structural, and optoelectronic properties of the solution-processed perovskite film. In this review, the state-of-the-art studies that focus on disclosing the key role of Pb source in the performance improvement of PSCs are systematically summarized. In addition, a comprehensive discussion on the effect of various Pb sources (e.g., Pb halides, Pb salts, Pb chalcogens, metallic Pb, and recycled Pb compounds) on the crystallization kinetics and photovoltaic characteristics of perovskite film is given. Also, the significant role of Pb source in producing large-scale PSCs in a controllable and sustainable manner is highlighted. This review is expected not only to put steps forward for the future commercialization of PSCs, but also to inspire more ideas in many other optoelectronic devices regarding raw material engineering.

Using a combination of gravure/flexographic printing and numerical modelling we evaluate the performance of conducting polymer/Ag hexagonal contact structures for large area flexible opto electronic devices. We take an efficient small area device and numerically estimate how device performance would change were the entire device stack upscaled. We dub this technique virtual upscaling.

Since their conception, organic electronic semiconductors have promised large area optoelectronic devices that can be mass produced at a fraction of the cost and embodied energy of devices made from traditional semiconductors. However, upscaling from small area lab-scale fabrication techniques to large area roll-to-roll (R2R) production has proved a substantial challenge. At the heart of this upscaling problem is the need for low cost, reliable contacts which can be readily printed. Device performance is often limited by the contacts, in terms of charge extraction efficiency and morphological compatibility of the sequentially deposited layers. Herein, high-speed R2R flexographic and gravure printing are combined with numerical device modeling to understand the performance of printed silver hexagonal contacts, and how contact design can affect final device performance. A strategy is presented which we dub “virtual upscaling” whereby the performance of the printed contact is virtually evaluated with an active layer material/device structure before the full device stack is printed. Through this methodology, a set of general design rules is developed which can be applied when experimentally optimizing contacts of optoelectronic devices. This approach has the potential to significantly reduce the number of design iterations and thus print runs when upscaling a structure.

Herein, it is described how semitransparent perovskite solar cells can be adapted to cope with specific and quite different requirements both for building integration and tandem photovoltaics. Clear guidelines for a rigorous device design based on “fitness-for-purpose” criteria are provided, together with some perspectives for future development by scanning the main challenges and issues to be addressed before commercialization.

Over the past decade, halide perovskite systems have captured widespread attention among researchers since their exceptional photovoltaic (PV) performance is disclosed. The unique combination of optoelectronic properties and solution processability shown by these materials has enabled perovskite solar cells (PSCs) to reach efficiencies higher than 25% at low fabrication costs. Moreover, PSCs display enormous potential for modern unconventional PV applications, since they can be made lightweight, semitransparent (ST), and/or flexible by means of appropriate design strategies. In particular, by enabling transparency and high efficiency simultaneously, ST-PSCs hold great promise for future versatile utilization in the context of building-integrated PVs (BIPVs) or as top cells to be coupled with conventional lower-bandgap bottom cells in tandem PV devices. The present review aims to provide a detailed overview of latest research about ST-PSCs for BIPVs and tandems, by critically reporting on the most updated and effective design strategies in view of these two possible future applications. The differences and similarities between the available approaches are punctually highlighted, emphasizing the importance of a rigorous application-orientated ST-PSC design. Finally, the main challenges and issues about device design, operation, and stability that need to be addressed before commercialization are thoroughly scanned.

Partial replacement (5–15%) of methylammonium (MA) in the MAPbI₃ perovskite by cesium or guanidinium (Gua) cations is demonstrated by X-ray diffraction, revealing shrinkage or expansion of the unit cell upon Cs or Gua incorporation, respectively. The power conversion efficiency improves from an average value of 18.6% for the MAPbI₃ to a value of 20.0% for the Cs_0.05Gua_0.05MA_0.90PbI₃ perovskite.

The overall impact of the partial replacement (5–15%) of methylammonium (MA) in the MAPbI₃ perovskite by cesium or guanidinium (Gua) cations to fabricate thin films of triple cation Cs _x Gua _y MA_1–x–y PbI₃ perovskites is studied. The structural changes are investigated by using X-ray diffraction measurements revealing shrinkage or expansion of the unit cell upon Cs or Gua incorporation, respectively. The optoelectronic properties are characterized with photoluminescence (PL) time-resolved spectroscopy and the space charge limited current (SCLC) method. Shorter PL time constants are obtained for the samples with only Cs, while longer PL decays are measured for the perovskites containing additional Gua cation. The SCLC measurements reveal a larger density of trap states in the Cs _x MA_1–x PbI₃ perovskites compared to the MAPbI₃ material. The PSCs fabricated with the different mixed cation Cs _x Gua _y MA_1–x–y PbI₃ perovskites reveal a good correlation with the measured optoelectronic properties. The power conversion efficiency (PCE) improves from an average value of 18.6% for the MAPbI₃ to a value of 20.0% for the Cs_0.05Gua_0.05MA_0.90PbI₃ perovskite with a champion cell delivering 21.2%. On the opposite, the PCE decreases to a value of 17.3% for the double cation perovskite with Cs.

Herein, surface modifications based on physical (UV−ozone, oxygen, argon, and/or helium plasma), chemical (interlayer passivation), and doping treatments and their impacts on the structural and optoelectronic properties of NiO _x are discussed. The effects of modified NiO _x films in p−i−n perovskite solar cells’ (PSCs’) power conversion efficiency (PCE) are also examined together with the current challenges and future outlooks.

The performances of perovskite solar cells (PSCs) largely depend on the perovskite compositions and the selection of electron and hole transport layers (ETLs and HTLs). The p-type NiO _x films are largely used as HTLs in p-i-n PSCs, thanks to their high transparency, processing versatility, cost-effectiveness, and easy integration within tandem devices. Several studies have shown that surface modifications on NiO _x films remove the surface defects, increase the NiO _x conductivity, and alter the band offset, consequently improving the interfaces between NiO _x films and the perovskite active layer. Indeed, besides improving the NiO _x intrinsic properties, the surface treatments also lead, in many cases, to superior perovskite quality driving high photovoltaic performance.

Herein, the authors demonstrate the use of bulky-sized, trifluoromethyl-group (CF₃) bearing benzylammonium iodide (CF₃BZA-I) and bromide (CF₃BZA-Br) molecules as surface passivators for formamidium-methylammonium-based perovskite films. CF₃BZA-I/Br passivated perovskite films exhibit larger grain size, lesser surface defects, and hydrophobic surface. The champion perovskite solar cell achieves an efficiency of ≈20.8% with significantly improved air- and photostability.

Solution-processed perovskite films are rich in surface defects and grain boundaries, which limits their performance and stability in photovoltaic application. Surface passivation using bulky organic cations can effectively reduce the surface defects of a perovskite film without affecting its fundamental properties. Herein, the use of hydrophobic bulky aromatic molecules, namely 4-trifluoromethyl-benzylammonium iodide/bromide (CF₃BZA-I/Br), as defect-passivators to heal the surface defects and grain boundaries of perovskite films is introduced. Owing to the presence of the trifluoromethyl (CF₃) moieties, CF₃BZA-I/Br-passivated perovskite films exhibit a hydrophobic surface with significantly fewer grain boundaries. By suppressing the surface and interfacial imperfections, CF₃BZA-Br-treated perovskite solar cells achieve an outstanding power conversion efficiency (PCE) of 20.75%. The PCE improvement originates mainly from the reduction of trap states and nonradiative carrier recombination. The ultrathin hydrophobic barrier layer formed after passivation also shields the perovskite film surface from moisture ingress and environmental degradation, leading to improved stability of the devices. By optimizing the passivation conditions, the bulky CF₃BZA-I/Br molecules could be the ideal defect passivators, with versatile applications in a wide variety of perovskite optoelectronics.

The acetate (Ac⁻) ions occupy lattice sites in the process of nucleation and crystallization of the perovskite, which effectively promotes the entry of formamidinium (FA⁺) into the lead halide octahedra to stabilize the α-phase of FAPbI₃. The solar cell based on the α-FAPbI₃ film presented a power conversion efficiency of 21.24% with negligible hysteresis.

The α-phase formamidinium lead triiodide (α-FAPbI₃)-based perovskite solar cells (PSCs) exhibit potential high efficiency due to their narrow bandgap, but the fabrication of a stable α-FAPbI₃ film still is challenging. Herein, a strategy is devised to achieve a stable α-FAPbI₃ film, in which lead acetate (PbAc₂) is added to the perovskite precursor solution. The Ac⁻ ions are involved in the formation of the lead halide octahedra, which effectively promotes the entry of FA⁺ into the lead halide octahedra to stabilize the α-phase of FAPbI₃. Furthermore, the Ac⁻ will gradually leave during the annealing process, thus the addition of PbAc₂ cannot introduce other components in the FAPbI₃. The crystallinity and crystal orientation of the perovskite films are also improved by the PbAc₂ additive to obtain low trap density films, leading to an increase in charge carrier collection. The champion solar cell based on the α-FAPbI₃ film presented a power conversion efficiency (PCE) of 21.24% with negligible hysteresis. After 500 h of storage under ambient conditions, the devices still maintained more than 90% of their initial efficiency.

This work concentrates on electron transport layer (ETL) and hole transport layer (HTL) free inverted perovskite solar cells. It is observed that eliminating the HTL is most critical for photovoltaic performance, compared with ETL-free and fully inverted solar cell configurations.

The selective contacts in perovskite solar cells play a major role in solar cell (SC) performance and optimization. Herein, the inverted architecture is focused on, where systematically the electron transport layer (ETL) and the hole transport layer (HTL) from the SC structure are eliminated. Three main architectures of the SCs are studied: a fully inverted structure, an ETL-free structure, and a HTL-free structure. Cathodoluminescence and photoluminescence are measured on various architectures, revealing the electron and hole injection efficiency from the perovskite to selective contacts. Moreover, surface voltage spectroscopy shows the type and the band-edge transition of these layers. Finally, the photovoltaic (PV) performance of different SCs shows that eliminating the HTL is most critical for PV performance, compared with ETL-free and fully inverted SC configurations. Current−voltage hysteresis curves prove that efficient selective contacts are essential to eliminate this phenomenon. Measuring the ideality factor shows that the dominant mechanism in ETL-free SCs is surface recombination, whereas in the other cases, it is Shockley–Reed–Hall recombination. This work provides knowledge about the functionality of methylammonium lead iodide as an electron conductor and as a hole conductor.

Recently, Förster resonance energy transfer (FRET)-based strategy has been successfully applied to improve the efficiencies of organic solar cells. However, the role of FRET has not been deconvolved unambiguously due to the complex excited state photophysics. Herein, a comprehensive view of the recent progress on FRET strategy is presented through analysis of those published examples including our works.

Recently, Förster resonance energy transfer (FRET)-based strategy has been successfully applied to promote the efficiencies of ternary blend organic solar cells (TOSCs). However, the intrinsic mechanism of FRET in the observed enhancement of efficiency has not been deconvolved unambiguously due to the complex photophysics mechanism. In this review, by deeply analyzing recent examples of FRET-incorporated TOSCs, diverse framework structures of FRET pairs are summarized, then the theory, prerequisites, and the confirmation methods for FRET are discussed. In particular, the role of FRET theory in the photoconversion process is discussed in detail, including exciton harvesting, exciton diffusion, and charge generation. Finally, the existing challenges and future research directions of FRET applications in TOSCs are proposed.

Nature Energy, Published online: 01 November 2021; doi:10.1038/s41560-021-00923-5

Formamidinium (FA)-based additives in precursor solutions suppressed the formation of the undesired δ phase during the crystallization of FAPbI₃ perovskites, and heat-induced permeation of 4-tert-butylbenzylammonium iodide (tBBAI) into inner perovskite grains stabilized the α structure. Solar cells assembled from this material exhibited improved power conversion efficiency and stability.

Abstract

α-Formamidinium lead iodide (α-FAPbI₃) is one of the most promising candidate materials for high-efficiency and thermally stable perovskite solar cells (PSCs) owing to its outstanding optoelectrical properties and high thermal stability. However, achieving a stable form of α-FAPbI₃ where both the composition and the phase are pure is very challenging. Herein, we report on a combined strategy of precursor engineering and grain anchoring to successfully prepare methylammonium (MA)-free and phase-pure stable α-FAPbI₃ films. The incorporation of volatile FA-based additives in the precursor solutions completely suppresses the formation of non-perovskite δ-FAPbI₃ during film crystallization. Grains of the desired α-phase are anchored together and stabilized when 4-tert-butylbenzylammonium iodide is permeated into the α-FAPbI₃ film interior via grain boundaries. This cooperative scheme leads to a significantly increased efficiency close to 21 % for FAPbI₃ perovskite solar cells. Moreover, the stabilized PSCs exhibit improved thermal stability and maintained ≈90 % of their initial efficiency after storage at 50 °C for over 1600 hours.

Alkyl-chain branching of non-fullerene acceptors flanking conjugated side-groups enables optimized optoelectronic and morphological properties, affording device performance of over 18%.

Abstract

Side-chain modifications of non-fullerene acceptors (NFAs) are essential for harvesting their full potential in organic solar cells (OSC). Here, an effective alkyl-chain-branching approach of the Y-series NFAs flanking meta-substituted phenyl side groups at the outer positions is demonstrated. Compared to BTP-4F-PC6 with linear m-hexylphenyl chains, two new acceptors named BTP-4F-P2EH and BTP-4F-P3EH are developed with bulkier alkyl chains branched at the β and γ positions, respectively. These branched chains result in altered molecular packing of the NFAs and afford higher open-circuit voltage of the devices. Despite the blue-shifted absorption of the branched-chain NFAs, their blends with PBDB-T-2F enable improved short-circuit current density for the corresponding devices owing to the more suitable phase separation and better exciton dissociation. Consequently, the OSCs based on BTP-4F-P2EH and BTP-4F-P3EH yield enhanced device performance of 18.22% and 17.57%, respectively, outperforming the BTP-4F-PC6-based ones (17.22%). These results highlight that the side-chain branching design of NFAs has great potential in optimizing molecular properties and promoting photovoltaic performance.

Homojunctions based on bipolar small π-conjugated molecules represent the ultimate stage of simplification of organic solar cells. Besides the fundamental questions posed by the possible direct photogeneration of charges–carriers and their transport, this concept can potentially contribute to the elimination of some of the major technical obstacles which limit the industrial scale development of organic photovoltaics.

Abstract

Single-material organic solar cells (SMOSCs) are on the forefront of research on organic photovoltaics (OPV). The generic term of SMOSCs encompasses a large variety of chemical structures implying very different basic concepts. Polydisperse «double cable» polymers and oligomers with acceptor groups linked to the conjugated backbone by a flexible spacer and donor–acceptor block copolymers are at present, the most investigated and efficient systems with spectacular progress in conversion efficiency achieved in the past 2–3 years. However, besides this mainstream SMOSCs research, a few recent publications describe OPV cells constituted of homojunctions based on small π-conjugated molecules. While the process of charge generation in such systems is still a matter of debate due in particular to the possible direct photogeneration of charge–carriers, devices with significant performance have been recently reported. After a brief overview of the most recent advances on the various types of SMOSCs, recent remarkable results on homojunction OPV cells based on small π-conjugated molecules are discussed in order to highlight the potential fundamental and technological interest of this emerging field of research.

Herein, three iodized diammonium spacers are selected to study the effects of chain length and heteroatom incorporation on the related interfacial properties of 2D/3D perovskite heterostructures. The structure tailoring and concentration control of organic spacers contribute to the well-controlled phase purity, improved quantum well orientation, and energetic band alignment at 2D/3D interfaces, and thus enhanced device efficiency.

Abstract

Perovskite solar cells (PSCs) based on 2D/3D heterostructures show great potential to combine the advantages of the high efficiency of 3D perovskites and the high stability of 2D perovskites. However, an in-depth understanding of the organic-spacer effects on the 2D quantum well (QW) structures and electronic properties at the 2D/3D interfaces is yet to be fully achieved, especially in the case of 2D perovskites based on diammonium spacers/ligands. Here, a series of diammonium spacers is considered for the construct ion 2D/3D perovskite heterostructures. It is found that the chemical structure and concentration of the spacers can dramatically affect the characteristics of the 2D capping layers, including their phase purity and orientation. Density functional theory calculations indicate that the spacer modifications can induce shifts in the energy-level alignments at the 2D/3D interfaces and therefore influence the charge-transfer characteristics. The strong intermolecular interactions between the 2,2-(ethylenedioxy)bis(ethylammonium) (EDBE) cations and inorganic [PbI₆]⁴⁻ slabs facilitate a controlled deposition of a phase-pure QW structure (n = 1) with a horizontal orientation, which leads to better surface passivation and carrier extraction. These benefits endow the EDBE-based 2D/3D devices with a high power conversion efficiency of 22.6% and remarkable environmental stability, highlighting the promise of spacer-chemistry design for high-performance 2D/3D PSCs.

An inverted perovskite solar cell employing a thermally-induced phase-change VO₂ electron extraction layer shows high efficiency of over 23% at high temperature and superior thermal stability simultaneously, which is mainly attributed to the dramatic change in the electrical properties and better electron extraction caused by the metal-to-insulator transition of VO₂ beyond its critical phase-change temperature.

Abstract

Reducing carrier recombination and facilitating charge extraction at the interface is of great significance to improve the device performance of perovskite solar cells (PSCs) towards commercial use. However, there has been little work done concerning transportation and recombination mechanism at the interface of the metal electrode and the electron transport layer in inverted PSCs. Herein, a new strategy of interface modification is reported that leverages the unique metal-to-insulator transition (MIT) characteristics of vanadium dioxide which is inserted as the electron extraction layer (EEL) in p-i-n planar PSCs. Benefiting from the suitable intermediate energy level of VO₂, the optimized device shows a power conversion efficiency (PCE) up to 22.11% with negligible hysteresis, as compared to the 20.96% benchmark at room temperature. Interestingly, the PCE of VO₂-based PSC increases to over 23% at 85 °C, which can be attributed to the dramatic change in the electrical properties and better electron extraction caused by the MIT of VO₂ beyond its critical phase-change temperature. In addition, the encapsulated VO₂-PSC shows superior thermal stability for 1000 h at 85 °C under 1 Sun illumination, maintaining over 90% of initial PCE. This work initiates the state-of-art concept of inserting thermally-induced phase-transition material as an EEL to achieve efficient and durable perovskite photovoltaics.

Here, an alternative additive (propylammonium chloride (PACl)) is reported to replace the commonly used methylammonium chloride for FAPbI₃ perovskite. The perovskite solar cell based on the PACl additive exhibits a power conversion efficiency of 22.22%, which is one of best efficiencies among the MA-free and Br-free perovskite solar cells.

Abstract

To achieve high efficiency perovskite solar cells (PSCs) based on α-phase formamidinium lead iodide (FAPbI₃), addition of methylammonium chloride (MACl) in the precursor solution is commonly used, mainly because of phase stability and improvement of grain size and crystallinity. However, the instability of MA in the perovskite limits the device long-term stability. In this report, n-propylammonium chloride (PACl) is proposed as an alternative to MACl for more stable and efficient FAPbI₃-based PSCs. Perovskite grain size is increased after addition of PACl. Unlike the MA cation, the propylammonium cation passivates the grain boundary rather than being incorporated into the perovskite lattice due to larger ionic size, which minimizes the change in bandgap. Carrier lifetime is significantly increased by more than five times from 405 to 2110 ns with the PACl additive with negligible trap-mediated recombination, while only four times longer carrier lifetime is observed by MACl additive. As a result, a power conversion efficiency over 22.2% is achieved by 20 mol% PACl additive, which is one of the best efficiencies among the MA-free and Br-free PSCs. In addition, stability against moisture is much better for PACl than for MACl due to an in situ formed barrier at the bulk perovskite.

The authors report a novel strategy co-modulation of crystallization and co-passivation of defects for FAPbI₃ perovskite solar cell, which gives a high PCE of 21.6% for the modified PSC (only 16.5% for the control device).

Abstract

Enhancing crystallinity, passivating the grain boundary and interfacial defects have been validated to be critical for improving the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). Herein, a synergetic co-modulation and co-passivation strategy is proposed to simultaneously enhance crystallinity and passivate the grain boundary and surface defects of FAPbI₃ based PSCs. The 4-fluoro-phenethylammonium iodide (4-F-PEAI) added in precursor solution and poly (9-vinylcarbazole) (PVK) added in antisolvent can jointly modulate the crystallization of FAPbI₃ films. The 4-F-PEAI-derived 2D perovskite, which is spontaneously formed at the grain boundaries of FAPbI₃, can passivate the defects effectively. In the meantime, PVK left on top of a FAPbI₃ layer can passivate the surface defects and meanwhile function as an interfacial barrier layer between FAPbI₃ and hole transport layer (HTL) to mitigate the detrimental interfacial charge recombination. With the holistic benefit of the enhanced crystallinity, reduced defects and trap sites, and mitigated non-radiative recombination and suppressed ion migration, the encouraging PCEs up to 21.6% is achieved for the resulting modified PSCs. Additionally, this strategy endows the device with notably enhanced operational stability under continuous exposure to illumination, with more than 84% of the initial PCE being maintained after continuous illumination for 800 h.

Transition metal oxides (TMOs) are expected to serve as carrier-selective transport layers for high-efficiency crystalline silicon (c-Si) solar cells. However, redox reactions or elemental migration at the c-Si/TMO interface tend to degrade the device performance. In this work, an ultra-thin SiO_X tunnel layer was intentionally introduced to suppress the redox reaction at c-Si/V₂O_X interface, demonstrating an efficiency up to 21.01%.

Abstract

Transition metal oxide (TMO) thin films featuring tunable work function, high transmittance, and simple fabrication process are expected to serve as carrier-selective transport layers for high-efficiency crystalline silicon (c-Si) solar cells. TMOs are prone to reaction or elemental migration with adjacent materials, which leads to uncontrollable optical and electrical properties. In this work, V₂O_X passivating contact, a promising hole transport layer (HTL) thanks to its high work function, is investigated and implemented in p-type c-Si solar cells. An ultrathin SiO_X tunnel layer is intentionally introduced by UV/O₃ pretreatment to suppress the redox reaction at c-Si/V₂O_X interface. Both saturation current density and contact resistance are reduced with the presence of UV-SiO_X due to the well tunned oxygen vacancies in SiO_X and V₂O_X thin films. The power conversion efficiency (PCE) based on p-Si/UV-SiO_X/V₂O_X/Ag rear contact achieves 21.01% with an increased open-circuit voltage of 635 mV and fill factor (FF) of 83.25%.

High-quality lead-free all-inorganic perovskite of CsSnBr₃ films with controlled grain boundaries are synthesized successfully on glass by a simple chemical vapor deposition method for smart photodetectors.

Abstract

The nonradiative recombination caused by the trap states at the grain boundaries (GBs) and surfaces directly limits the photoelectronic performance of lead-free all-inorganic perovskites films. In this work, the typical CsSnBr₃ films with controlled GBs and surfaces are prepared successfully on glass by a solid-source chemical vapor deposition method. The grain size of CsSnBr₃ films increases with the increase of growth temperature, indicating the reduction of GBs. Time-resolved photoluminescence spectra show that the lifetime of photogenerated carrier is longer in the large-grain-size CsSnBr₃ film. Furthermore, the photodetector based on CsSnBr₃ film with decreased GBs shows excellent performance with photocurrent up to 760 nA, responsivity up to 9200 mA W⁻¹, and fast response times of 5/12 ms under the illumination of 405 nm laser. Moreover, the photodetector is also fabricated on a flexible substrate, demonstrating a good bending stability. This work provides a guideline in the growth of high-quality perovskites films with controlled GBs and surfaces for next-generation high-performance photoelectronic devices.

Hybrid perovskites based pigments are attractive semiconductors for photovoltaic applications. In this work, the negative capacitance features are quantified in a triple-cation-based perovskite. Perovskite solar cells are fabricated with and without poly(3-hexylthiophene) [P3HT] as hole transport layer (HTL). It is noted that the solar cells without HTL show significant hysteresis, while the negative capacitance appears in the low-frequency regime.

Abstract

Understanding the device kinetics occurring in the bulk and at the charge selective interfaces is vital for optimizing the performance of perovskite solar cells (PSCs) and their development. Planar PSCs are studied with and without hole transport layer (HTL) and power conversion efficiency of 16.23% is measured with poly(3-hexylthiophene) [P3HT] as HTL, while the PSCs without HTL show significant hysteresis. A comprehensive electrical response of the PSCs is investigated. The bias-dependent electrochemical impedance spectroscopy (EIS) reveals the appearance of the negative capacitance in the low-frequency regime. The modification of the low-frequency PSCs response accompanied by a further decrease in recombination resistance is due to the interfacial interactions between the migrating ions and the metal contact. The doped and undoped P3HT layers impede this interaction which explains the absence of the negative capacitance at lower applied voltages. The investigation provides an understanding of the physical processes behind the negative capacitance.

Interface Passivation

In article number 2101662, Furkan H. Isikgor, Stefaan De Wolf and co-authors develop a NiO _x /perovskite interface passivation strategy using an organometallic dye (N719) molecule. It concurrently passivates both NiO _x and perovskite traps and facilitates charge transport across the interface. The self-assembling nature of N719 allows conformally covering complex surfaces and fabrication of highly efficient textured perovskite/silicon tandem solar cells.

A 3D optical simulation study is reported that predicts average visible transmission and ideal J _SC values of semi-transparent organic photovoltaics (ST-OPVs) with porous silver nanowire top electrodes, thereby leading to the highest light utilization efficiency value in ST-OPVs reported to date.

Abstract

A key factor in improving semi-transparent organic photovoltaics (ST-OPVs) performance is achieving high light utilization efficiency (LUE). However, device performance can also be limited by the lack of understanding of light transmission and reflection within the device architecture, and the transmission of the top electrode in particular. Here, highly efficient ST-OPVs are reported via the rational design of silver nanowire (Ag NW) top electrodes via 3D optical simulation. Due to its careful consideration for the ST-OPV of the effect of the Ag NW networking structure, estimated average visible transmission (AVT) and ideal short-circuit current density values from 3D optical simulation closely match those from actual measurements. Optimized ST-OPVs with Ag NW porosity of 20% and active layer thickness of 150 nm exhibit LUE of 4.15% with a power conversion efficiency of 9.7% and AVT of 42.82%. This work achieves a record-high LUE in ST-OPVs reported to date and the first report introducing a 3D optical simulation study.

A conjugated copolymer characteristic of alternating N-annulated perylene and 3,4-ethylenedioxythiophene backbones is prepared via direct arylation polycondensation and used for the fabrication of 21.7%-efficiency, 85 °C durable perovskite solar cells. This study demonstrates the importance of developing a hole-transporting material, which is not only morphologically heat-resistant but also can control the thermal decomposition of organic–inorganic hybrid perovskites.

Abstract

Organic–inorganic hybrid perovskites in high-efficiency solar cells are prone to degradation at elevated temperatures, especially in the presence of water moisture. A hole-transporting conjugated copolymer (abbreviated as p-NP-E) characteristic of alternating N-annulated perylene and 3,4-ethylenedioxythiophene backbones, to achieve thermostable perovskite solar cells (PSCs) via controlling gas permeation and thus perovskite decomposition is reported. p-NP-E can be conveniently prepared via Pd-catalyzed direct arylation polycondensation. The air-doped p-NP-E composite film containing nonvolatile 4-tert-butylpyridinium bis(trifluoromethanesulfonyl)imide presents a higher hole mobility and an improved conductivity in comparison with the control based on the state-of-the-art polymer, p-TAA, leading to more efficient PSCs. More critically, the p-NP-E based hole transport layer is not only morphologically more heat-resistant, but also features a lower solubility coefficient and diffusion coefficient of both environmental water molecules and gaseous products such as CH₃I and CH₃NH₂ from the thermal decomposition of perovskite, enabling the fabrication of 21.7%-efficiency, 85 °C durable solar cells.

In this study it is reported an electroluminescent solar cell using CsPbI₃ quantum dots (QDs) via solid-state-ligand exchange process using organic ligand triphenyl phosphite; the device achieves a champion efficiency of 15.21%, and an overall electric power to light conversion efficiency of 3.80% in red light-emitting diode function, a record value for QD photovoltaics.

Abstract

All-inorganic CsPbX₃ (X = Cl, Br, I, or mixed halides) perovskite quantum dots (QDs) exhibit tunable optical bandgaps and narrow emission peaks, which have received worldwide interest in the field of both photovoltaics (PVs) and light-emitting diodes (LEDs). Herein, it is reported a discovery that CsPbI₃ perovskite QD solar cell can simultaneously deliver high PV performance and intense electroluminescence. In specific, the multifunctional CsPbI₃ QD film is fabricated through a simple yet efficient solid-state-ligand exchange process using a tailored organic ligand triphenyl phosphite (TPPI). The function of QD surface manipulation using TPPI here is proven to be twofold, balancing the carrier transport and effectively passivating the QD surface to produce conductive and emissive QD film. The CsPbI₃ perovskite QD solar cell delivers a champion efficiency of 15.21% with improved open circuit voltage and high fill factor. Concurrently functioning as a red LED, the CsPbI₃ perovskite QD solar cell outputs electric power to light conversion efficiency approaching 4%, a record value for QD electroluminescent PVs. The results here indicate that these versatile perovskite QDs may be a promising candidate for fabricating multifunctional optoelectronic devices.

To increase solar production in city centers, one either needs to increase the power generation per unit area or increase the harvesting area by utilizing the building façade for solar electricity generation. Perovskite solar cells (PSCs) appear to be an ideal solution for building-integrated photovoltaics (BIPVs), which transforms windows or façades into electric power generators.

Abstract

The rapid emergence of organic–inorganic lead halide perovskites for low-cost and high-efficiency photovoltaics promises to impact new photovoltaic concepts. Their high power conversion efficiencies, ability to coat perovskite layers on glass via various scalable deposition techniques, excellent optoelectronic properties, and synthetic versatility for modulating transparency and color allow perovskite solar cells (PSCs) to be an ideal solution for building-integrated photovoltaics (BIPVs), which transforms windows or façades into electric power generators. In this review, the unique features and properties of PSCs for BIPV application are accessed. Device engineering and optical management strategies of active layers, interlayers, and electrodes for semitransparent, bifacial, and colorful PSCs are also discussed. The performance of PSCs under conditions that are relevant for BIPV such as different operational temperature, light intensity, and light incident angle are also reviewed. Recent outdoor stability testing of PSCs in different countries and other demonstration of scalability and deployment of PSCs are also spotlighted. Finally, the current challenges and future opportunities for realizing perovskite-based BIPV are discussed.