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Nature Photonics, Published online: 17 January 2022; doi:10.1038/s41566-021-00931-7

Hybrid cathode interlayer composed of PNDIT-F3N:PDIN (0.6:0.4, in wt%) is applied in organic solar cells with PM6:Y6 as the active layer, and a power conversion efficiency of 17.4% is attained, outperforming devices with interlayers such as NDI-M, PDINO, and Phen-DPO. The hybrid strategy is demonstrated as an efficient approach to improve the performance of organic solar cells with nonfullerene acceptors.

Abstract

With the emergence of fused ring electron acceptors, the power conversion efficiency of organic solar cells reached 19%. In comparison with the electron donor and acceptor materials progress, the development of cathode interlayers lags. As a result, charge extraction barriers, interfacial trap states, and significant transport resistance may be induced due to the unfavorable cathode interlayer, limiting the device performances. Herein, a hybrid cathode interlayer composed of PNDIT-F3N and PDIN is adopted to investigate the interaction between the photoexcited acceptor and cathode interlayer. The state of art acceptor Y6 is chosen and blended with PM6 as the active layer. The device with hybrid interlayer, PNDIT-F3N:PDIN (0.6:0.4, in wt%), attains a power conversion efficiency of 17.4%, outperforming devices with other cathode interlayer such as NDI-M, PDINO, and Phen-DPO. It is resulted from enhanced exciton dissociation, reduced trap-assisted recombination, and smaller transfer resistance. Therefore, the hybrid interlayer strategy is demonstrated as an efficient approach to improve device performance, shedding light on the selection and engineering of cathode interlayers for pairing the increasing number of fused ring electron acceptors.

Conjugated mesopolymer is first applied in non-fullerene solar cells. The champion device based on MePBDFCl _H /Y6 shows a power conversion efficiency (PCE) of 15.06%, which is attributed to the efficient intermolecular charge transfer. Meanwhile, the champion PCE is a new record for benzo[1,2-b:4,5-b′]difuran-based organic solar cells. More importantly, the batch-to-batch variation is effectively reduced by adopting mesopolymer.

Abstract

The high-performance organic solar cells (OSCs) tend to choose the polymers with high molecular weight as donors, which easily produce good crystallinity to facilitate intermolecular charge transfer. However, these polymers usually accompanied by the low solubility and synthetic difficulty, increasing batch-to-batch variations. The proposal of conjugated mesopolymers (molar mass (M _n) in 1–10 kDa) can overcome these problems. Herein, a new mesopolymer, MePBDFCl _H as donor material is designed and synthesized, and firstly applied in OSCs. As a comparison, other lower molecular weight mesopolymer of MePBDFCl _L and higher molecular weight polymer of PBDFCl with same structure are also prepared and investigated. Because of its appropriate phase separation and miscibility in the blend film, the MePBDFCl _H exhibits the highest power conversion efficiency (PCE) of 15.06% among the three materials. Meanwhile, the champion PCE is a new record for benzo[1,2-b:4,5-b′]difuran-based photovoltaic materials. Importantly, comparing to the pronounced PCE decrease of polymer PBDFCl by about 12%, a slightly PCE difference for mespolymer MePBDFCl _L is only less than 5%, reducing the batch-to-batch variation. This work not only suggests that the benzo[1,2-b:4,5-b′]difuran unit is a promising electron-donating core but also shows that the mesopolymers have great potentials to produce the low-differentiated and high-performance organic photovoltaic materials.

Organic Solar Cells

In article number 2102394, Dan Deng, Xiaohui Qiu, Zhixiang Wei and co-workers introduce a polymerized small-molecule acceptor into all-small-molecule organic solar cells as an interface modulator. An enhanced power conversion efficiency over 15% is achieved by improved charge transportation and condensed morphology. This work provides useful guidance for the interface modulator strategy in organic solar cells.

All-Polymer Solar Cells

In article number 2103239, Bumjoon J. Kim, Yun-Hi Kim and co-workers develop a series of polymer acceptors with controlled backbone regioregularities and side chain structures. All-polymer solar cells based on a RRg-C20 acceptor which has a regioregular backbone and optimal side chain length achieve a high power conversion efficiency of 15.12%, attributed to high electron mobility and optimal blend morphology.

Highly efficient durable nonfullerene organic solar cells (OSCs) are achieved with a new cathode interlayer based on biradical-forming phenol-functionalized perylene bisimides. These OSCs take advantage of good compatibility between the interlayer material and Y6 electron acceptor dyes and good interlayer thickness tolerance.

Abstract

A new type of cathode interlayer composed of 2,6-di-tert-butyl-phenol-functionalized perylene bisimide (PBI-2P) is successfully applied as an electron transporting layer for fused-ring nonfullerene organic solar cells (OSCs). The stable contact between these novel electron transporting layers and the representative nonfullerene acceptor Y6 greatly enhances the device stability compared to conventional amine-group containing cathode interlayers. Moreover, the easily formed biradical species in the interlayers yields rather good thickness tolerance of the PBI-2P layer in photovoltaic devices. The OSCs based on the PBI-2P interlayer show a power conversion efficiency up to 17.20% and good stability compared to amino-group functionalized interlayers. The findings demonstrate a promising design principle for cathode interlayer engineering based on pigment chromophores equipped with the 2,6-di-tert-butylphenoxy groups that are prone to form the respective ultrastable butylphenoxy radicals for stable nonfullerene OSCs.

By introducing ClFA⁺ cation to reduce the voltage loss of perovskite front subcell and using chloride substitution to broaden the absorption spectra of organic rear subcell, a monolithic perovskite/organic tandem solar cell is constructed, and the power conversion efficiency reaches 22.0%.

Abstract

Combining the high stability under UV light of the wide bandgap (WBG) perovskite solar cells (pero-SCs) and the broad near-infrared absorption spectra of the narrow bandgap (NBG) organic solar cells (OSCs), the perovskite/organic tandem solar cells (TSCs) with the WBG pero-SC as front cell and the NBG OSC as rear cell have attracted attention . However, the photovoltaic performance of the perovskite/organic TSCs needs to be further improved. Herein, nonradiative charge recombination loss is reduced through bulk defect passivation in the WBG pero-SC front subcell and broadening the range of absorption spectra of the NBG OSC rear cell. For the WBG pero-SCs, an organic cation chloro-formamidinium is introduced into FA_0.6MA_0.4Pb(I_0.6Br_0.4)₃ to passivate the bulk defects in the perovskite film and the WBG pero-SC displays high open-circuit voltage of 1.25 V and high fill factor of 83.0%. For the NBG OSCs, a new infrared-absorbing organic small molecule acceptor BTPV-4Cl-eC9 is designed and synthesized. Then, a monolithic perovskite/organic TSC is fabricated with the WBG pero-SC as the front cell and the NBG OSC as the rear cell, and the TSC demonstrates high power conversion efficiency up to 22.0%. The results indicate that the perovskite/organic TSC is promising for future commercialization.

This work reviews the recent developments in the field of perovskite-silicon tandems, explores the feasibility to elevate efficiency to >32%, analyzes the upscaling technology being compatible with the current silicon technology, and discusses the pathways to prolong its stability.

Abstract

This review focuses on monolithic 2-terminal perovskite-silicon tandem solar cells and discusses key scientific and technological challenges to address in view of an industrial implementation of this technology. The authors start by examining the different crystalline silicon (c-Si) technologies suitable for pairing with perovskites, followed by reviewing recent developments in the field of monolithic 2-terminal perovskite-silicon tandems. Factors limiting the power conversion efficiency of these tandem devices are then evaluated, before discussing pathways to achieve an efficiency of >32%, a value that small-scale devices will likely need to achieve to make tandems competitive. Aspects related to the upscaling of these device active areas to industry-relevant ones are reviewed, followed by a short discussion on module integration aspects. The review then focuses on stability issues, likely the most challenging task that will eventually determine the economic viability of this technology. The final part of this review discusses alternative monolithic perovskite-silicon tandem designs. Finally, key areas of research that should be addressed to bring this technology from the lab to the fab are highlighted.

Theoretical calculations reveal that the appropriate extension of the alkyl chain provides a new perspective for the design of passivation molecules. The perovskite surface adsorbed by 2-MDEP shows steady Pb-N and Pb-S interactions during the ab initio molecular dynamics process, which indicates better long-term stability of passivation effects in perovskite solar cells under humidity.

Abstract

Contemporary perovskite solar cells (PSCs) have drawn substantial interest due to their high photovoltaic efficiency. However, the instability of perovskite in a humid environment restricts the service time extension and limits the large-scale application of PSCs. Herein, a series of passivation molecules (PMs), 2-MEP, 2-MDEP, 2-MTEP, and 2-MQEP, featuring different lengths of alkyl chains have been designed based on 2-mercaptopyridine (2-MP) which greatly improve the stability of PSCs in the humid environment. First-principles calculations demonstrate that the designed molecules offer stronger adsorption on the perovskite surface compared with 2-MP. The charge density difference and Bader charge analysis show that the newly designed Lewis bases improve the charge transfer ability, leading to effective separation of carriers at PM@MAPbI₃ interfaces. Furthermore, molecular dynamics simulations verify that the steady Pb-N/S interactions in the MAPbI₃/PM/H₂O system effectively prevent H₂O from approaching the perovskite surface. This work not only provides a set of promising surface passivators (especially 2-MDEP), but also paves a way for the design of PMs that endow PSCs stability and make PSCs highly competitive in the photovoltaic market.

Publication date: April 2022

Source: Nano Energy, Volume 94

Author(s): Zhihao Li, Zhenhan Wang, Chunmei Jia, Zhi Wan, Chongyang Zhi, Can Li, Meihe Zhang, Chao Zhang, Zhen Li

Publication date: April 2022

Source: Nano Energy, Volume 94

Author(s): Sanwan Liu, Rui Chen, Xueying Tian, Zhichun Yang, Jing Zhou, Fumeng Ren, Shasha Zhang, Yiqiang Zhang, Mengfan Guo, Yang Shen, Zonghao Liu, Wei Chen

A quaternary organic solar cell (OSC) is reported by using two polymer donors (PM6 and L20) along with acceptors Y6 and PC₇₁BM, leading to improvements of opencircuit voltage, fill factor, and power conversion efficiency. The quaternary OSC exhibits a higher charge collection efficiency, expedited charge carrier sweep-out, and reduced charge recombination losses. The suppression on ΔV _oc is attributed to reduced ΔE ₂ (0.143 eV) and ΔE ₃ (0.216 eV).

Multi-component organic solar cells (OSCs) composing of more than two donor and acceptor materials have attracted increasing attention, due to the possibilities to further mitigate voltage loss (ΔV _oc) for the gain of open-circuit voltage (V _oc). However, the control of phase morphology in multi-component blend systems that critically impacts ΔV _oc and the ultimate power conversion efficiency (PCE) is still a challenge. Here, we report a quaternary blend-based strategy for non-fullerene OSCs by using two polymer donors (PM6 and L20) along with acceptors of a non-fullerene (Y6) and PC₇₁BM, leading to concurrent improvements of the V _oc, device fill factor and eventual PCE. The quaternary OSC exhibits the advantages of a higher charge collection efficiency, expedited charge carrier sweep-out, and reduced charge recombination losses. The suppression on ΔV _oc is attributed to the reduced radiative recombination loss below the bandgap (0.143 V) and non-radiative voltage loss (0.216 V). These properties are linked to synergies of modified energetics and film morphology of the quaternary blends. This work demonstrates that incorporating suitable donor and acceptor guest molecules to organic binary blend systems is a highly viable approach for lowering the energy loss in organic bulk heterojunctions towards the boost of photovoltaic performance for realistic energy conversion applications.

Herein, the possible grain growth mechanism in wetting (PEDOT:PSS) and nonwetting (PEDOT:PSS/PTAA) surfaces is presented. The nonwetting surface facilitates the formation of big perovskite grains, as the crystallization process dominates the nucleation process. In contrast, the reverse happens with wetting surfaces, yielding small-grain perovskite.

Because of their inferior film quality, Pb–Sn-mixed low-bandgap (LBG) perovskites suffer from poor charge transportation, compromising photovoltaic parameters of final solar cells. Herein, an approach to improve the quality of the charge interface layer is proposed, in which a thin layer of hydrophobic [bis (4-phenyl) (2, 4, 6-trimethylphenyl) amine] (PTAA) is inserted between the hole-selective layer of hydrophilic poly (3, 4-ethylenedioxythiophene) -polystyrenesulfonicacid (PEDOT:PSS) and LBG perovskite layer. The introduction of a tiny layer of the hydrophobic PTAA acts as a shield layer to protect the underlying acidic PEDOT:PSS layer from moisture-related degradation and works as an intermediary layer to facilitate the growth of significantly larger perovskite grains; these enlarged grains are indicative of enhanced crystallinity and fewer grain boundaries in the perovskite layer. The fewer grain boundaries lead to suppression of interfacial defects and result in enhanced charge collection at the hole transport layer/perovskite interface, thus improving the open-circuit voltage up to 0.85 V and fill factor up to ≈78%, eventually boosting the power conversion efficiency of the champion cell up to 19.08%. Herein, a simple interface engineering route to fabricate efficient and stable Pb–Sn-mixed LBG perovskite solar cells is offered.

Liquid crystal 4((6(acryloyloxy)hexyl)oxy)benzoic acid (6OBA) is introduced as an intelligent temperature-sensitive template to simultaneously enhance the large-scale printability of perovskite inks and the quality of perovskite film for improving the efficiency and mechanical stability of perovskite solar cells (PSCs). The optimized PSCs with 6OBA exhibit superior efficiency of 19.87% for flexible devices (1.01 cm²) and 14.74% for flexible modules (25 cm²).

The control of crystallization and printability of large-area perovskite layers is crucial to facilitating their commercial development in flexible electronics. Considering the benefits of the liquid crystals with intelligent temperature sensitivity for the printable and crystalline template of a scalable perovskite film, a liquid crystal 4((6(acryloyloxy)hexyl)oxy)benzoic acid (6OBA) is introduced. The 6OBA shows a liquid crystal temperature range matching with the thermal annealing temperature of perovskite films. A desire printability of perovskite inks for scalable and homogeneous devices is guaranteed due to the fluidity of the 6OBA additive at room temperature. Moreover, the crystalline 6OBA promotes crystallization of perovskite films during the thermal annealing process, which can also release the residual stress of the whole layer. The optimized perovskite solar cells (PSCs) with 6OBA exhibit superior power conversion efficiency values of 19.87% for flexible devices (1.01 cm²) and 14.74% for flexible modules (25 cm²). The unencapsulated devices can maintain >90% of their original efficiency after 1500 h in the ambient atmosphere. Furthermore, the flexible PSCs exhibit outstanding bending resistance, retaining over 88% of their initial efficiency after 1000 bending cycles at a radius of 3 mm. This work provides a facile strategy for accelerating the development of flexible electronics.

A tight packing in the mixing region effectively enhances the hole transfer and leads to the enlarged and narrow electron density of state. The optimized electronic structure effectively increases carrier density and reduces the recombination losses due to the reduced energy disorder, improving the open-circuit voltage, short-circuit current and fill factor simultaneously.

Abstract

The donor/acceptor interaction in non-fullerene organic photovoltaics leads to the mixing domain that dictates the morphology and electronic structure of the blended thin film. Initiative effort is paid to understand how these domain properties affect the device performances on high-efficiency PM6:Y6 blends. Different fullerenes acceptors are used to manipulate the feature of mixing domain. It is seen that a tight packing in the mixing region is critical, which could effectively enhance the hole transfer and lead to the enlarged and narrow electron density of state (DOS). As a result, short-circuit current (J _SC) and fill factor (FF) are improved. The distribution of DOS and energy levels strongly influences open-circuit voltage (V _OC). The raised filling state of electron Fermi level is seen to be key in determining device V _OC. Energy disorder is found to be a key factor to energy loss, which is highly correlated with the intermolecular distance in the mixing region. A 17.53% efficiency is obtained for optimized ternary devices, which is the highest value for similar systems. The current results indicate that a delicate optimization of the mixing domain property is an effective route to improve the V _OC, J _SC, and FF simultaneously, which provides new guidelines for morphology control toward high-performance organic solar cells.

Based on the superior properties of perovskite quantum dots (PQDs) over bulk perovskites, not only the applications of PQDs in perovskite quantum solar cells (PQDSCs), outlining the engineering concerning surface ligands, additives and hybrid composition are reviewed, but also their various roles in other photovoltaic devices, including photo conversion layer, interface layer and additive are presented.

Abstract

Perovskite quantum dots (PQDs) have captured a host of researchers’ attention due to their unique properties, which have been introduced to lots of optoelectronics areas, such as light-emitting diodes, lasers, photodetectors, and solar cells. Herein, the authors aim at reviewing the achievements of PQDs applied to solar cells in recent years. The engineering concerning surface ligands, additives, and hybrid composition for PQDSCs is outlined first, followed by analyzing the reasons of undesired performance of PQDSCs. Subsequently, a novel overview that PQDs are utilized to improve the photovoltaic performance of various kinds of solar cells, is provided. Finally, this review is summarized and some challenges and perspectives concerning PQDs are also discussed.

Fluorine substitution increases the interaction with ZnO and accelerates the photon decomposition of A-D-A type (nonfullerene acceptor) NFA, while he β-alkyl chains on the thiophene unit next to the C═C linker improves the stability of acceptor molecules by forming protecting atomic cage. When using PET-treated ZnO and L8-BO as the electron acceptor, T ₈₀ was estimated over 5000 h.

Abstract

Despite the tremendous efforts in developing non-fullerene acceptor (NFA) for polymer solar cells (PSCs), only few researches are done on studying the NFA molecular structure dependent stability of PSCs, and long-term stable PSCs are only reported for the cells with low efficiency. Herein, the authors compare the stability of inverted PM6:NFA solar cells using ITIC, IT-4F, Y6, and N3 as the NFA, and a decay rate order of IT-4F > Y6 ≈ N3 > ITIC is measured. Quantum chemical calculations reveal that fluorine substitution weakens the C═C bond and enhances the interaction between NFA and ZnO, whereas the β-alkyl chains on the thiophene unit next to the C═C linker blocks the attacking of hydroxyl radicals onto the C═C bonds. Knowing this, the authors choose a bulky alkyl side chain containing molecule (named L8-BO) as the acceptor, which shows slower photo bleaching and performance decay rates. A combination of ZnO surface passivation with phenylethanethiol (PET) yields a high efficiency of 17% and an estimated long T ₈₀ and Ts₈₀ of 5140 and 6170 h, respectively. The results indicate functionalization of the β-position of the thiophene unit is an effective way to improve device stability of the NFA.

Charge transport behavior of two amine Cu porphyrin supramolecules with different stacking interactions in perovskite grain boundaries was investigated in detail. Results prove that the construction of homogeneously large polarons (HLPs) in aromatic passivators is a key factor for the charge transport between perovskite grains. This work also affords a new strategy to design new optoelectronic materials with improved charge mobilities.

Abstract

Aromatic passivators, such as porphyrin, with large π-backbones have attracted considerable attention to boost the charge carrier in polycrystalline perovskite films, thus enabling the fabrication of efficient and stable perovskite solar cells (PSCs). However, they often self-assemble into supramolecules that probably influence the charge-transfer process in the perovskite grain boundary. Here, by doping a monoamine Cu porphyrin into perovskite films, two porphyrin-based self-assembled supramolecules were successfully prepared between perovskite grains. Crystal structures and theoretical analyses reveal the presence of a stronger interaction between the amine units and the central Cu ions of neighbouring porphyrins in one of the supramolecules. This has a modified effect on the dipole direction of the porphyrins to be quantized as homogeneously large polarons (HLPs) in a periodic lattice. The porphyrin supramolecules can stabilize perovskite grain boundaries to greatly improve the stability of PSCs, while the HLPs-featured supramolecule facilitates hole transport across perovskite grains to remarkably increase the cell performance to as high as 24.2 %. This work proves that the modulation of the intermolecular interaction of aromatic passivators to yield HLPs is crucial for the cascaded acceleration of charge transport between perovskite grains.

Perovskite Solar Cells

In article number 2103175, Young S. Park, Sungjun Hong and co-workers design a halogenated phenothiazine based self-assembled monolayer as a new type of hole transporting layer in inverted perovskite solar cells, displaying an energetically well aligned interface with the light absorbing perovskite top layer. The advantage of halogenated phenothiazine is that it provides an efficient interfacial defect passivation for fast charge transport with minimal recombination, which can lead to improved efficiency and excellent long-term stability.

A polymer donor PBDF-NS is synthesized by using naphthalene-substituted benzo[1,2-b:4,5-b′]difuran (BDF) and fluorinated benzotriazole units. PBDF-NS possesses a low-lying HOMO level of −5.44 eV and a wide bandgap of 1.87 eV. Enormous progress in efficiency are achieved from 14% to over 16%, which are the highest efficiencies for BDF copolymer-based organic solar cells.

Abstract

Molecular design of polymer donors is of vital importance for obtaining high-performance organic solar cells (OSCs). At present, much of the important progress in power conversion efficiencies (PCEs) achieved for OSCs has been associated with the benzodithiophene (BDT)-based polymers, while the highest PCE of benzo[1,2-b:4,5-b′]difuran (BDF) polymer-based OSCs only reaches 14.0%. Here, a polymer donor named PBDF-NS is designed and synthesized by using naphthalene-substituted benzo[1,2-b:4,5-b′]difuran as the electron-sufficient units and fluorinated benzotriazole (BTz) as the electron-deficient units. PBDF-NS possesses a low-lying HOMO level of −5.44 eV and a wide bandgap of 1.87 eV. When using LC301 as the acceptor, PBDF-NS-based OSC exhibits an excellent PCE of 15.24%. Moreover, the ternary and all-polymer devices based on PBDF-NS both achieve a higher PCE over 16%, which represents the highest efficiency values reported for BDF polymer-based OSCs in the literature thus far. Meanwhile, the binary and ternary devices all display excellent storage and light-soaking stabilities. The results demonstrate that by rational molecular design, BDF-based copolymers can be comparable to or even surpass the performance of BDT-based counterparts and also show great potential for realizing high-efficiency all-polymer solar cells.

Perovskite Solar Cells

Light-intensity analysis of JV parameters is introduced by Yulia Galagan and Damian Glowienka in article number 2105920 as a simple method to allow understanding of the dominating mechanisms that limit device performance in perovskite solar cells. The method is based on the drift–diffusion model and is aimed at helping in the explanation of parasitic losses from trap-assisted recombination or ohmic losses in devices.

Publication date: April 2022

Source: Nano Energy, Volume 94

Author(s): Pengyang Wang, Bingbing Chen, Renjie Li, Sanlong Wang, Yucheng Li, Xiaona Du, Ying Zhao, Xiaodan Zhang

Perovskite single crystals (SCs) are grown on-demand at room temperature and integrated directly onto optoelectronic devices via printing and coating using a scalable cosolvent evaporation (CSE) strategy. The CSE strategy controls supersaturation and suppresses competing nucleation during drying to yield high-quality SCs of 2D, 3D, lead-free, and mixed-ion perovskites with minimal residue.

Abstract

Solution-processed metal halide perovskite (MHP) single crystals (SCs) are in high demand for a growing number of printed electronic applications due to their superior optoelectronic properties compared to polycrystalline thin films. There is an urgent need to make SC fabrication facile, scalable, and compatible with the printed electronic manufacturing infrastructure. Here, a universal cosolvent evaporation (CSE) strategy is presented by which perovskite SCs and arrays are produced directly on substrates via printing and coating methods within minutes at room temperature from drying droplets. The CSE strategy successfully guides the supersaturation via controlled drying of droplets to suppress all crystallization pathways but one, and is shown to produce SCs of a wide variety of 3D, 2D, and mixed-cation/halide perovskites with consistency. This approach works with commonly used precursors and solvents, making it universal. Importantly, the SC consumes the precursor in the droplet, which enables the large-scale fabrication of SC arrays with minimal residue. Direct on-chip fabrication of 3D and 2D perovskite photodetector devices with outstanding performance is demonstrated. The approach shows that any MHP SC can now be manufactured on substrates using precision printing and scalable, high-throughput coating methods.

Herein, a unique SnO₂ layer to protect the underlaying layers from damage of the sputtered transparent electrode is developed. Moreover, a high-near-infrared transparent perovskite solar cell using cerium-doped indium oxide is prepared, achieving a record power conversion efficiency (PCE) of 17.23%. As a result, a four-terminal perovskite/silicon tandem solar cell with a PCE of 26.14% is obtained.

Two issues need to be resolved when fabricating p–i–n semitransparent perovskite solar cells (ST-PVSCs) for four-terminal (4 T) perovskite/silicon tandem solar cells: 1) damage to the underlying absorber (MAPbI₃), electron transporting layer ([6,6]-phenyl-C₆₁-butyric acid methyl ester, PCBM), and work function (WF) modifier (polyethylenimine, PEI), resulting from the harsh sputtering conditions for the transparent electrodes (TEs) and 2) low average near-infrared transmittance (ANT) of TEs. Herein, a unique SnO₂ layer to protect the MAPbI₃ and PCBM layers is developed and functions as a WF modifier for a new TE (cerium-doped indium oxide, ICO), which exhibits an excellent ANT of 86.7% in the range of 800−1200 nm. Moreover, a MAPbI₃-based p–i–n ST-PVSC is prepared, achieving an excellent power conversion efficiency (PCE) of 17.23%. When it is placed over the Si solar cell, a 4 T tandem solar cell with a PCE of 26.14% is obtained.

Solar cells comprised of a lead-free Cs₂AgBiBr₆-based 2D/3D hybrid double perovskite with PEA⁺ as constituting cation show an increase of the power conversion efficiency by almost 10% due to a large increase in the V _OC. This is attributed to a better contact selectivity caused by an improved energy level alignment at the interface between the perovskite layer and the hole-transporting material.

Abstract

Since their introduction in 2017, the efficiency of lead-free halide perovskite solar cells based on Cs₂AgBiBr₆ has not exceeded 3%. The limiting bottlenecks are attributed to a low electron diffusion length, self-trapping events and poor selectivity of the contacts, leading to large non-radiative V _OC losses. Here, 2D/3D hybrid double perovskites are introduced for the first time, using phenethyl ammonium as the constituting cation. The resulting solar cells show an increased efficiency of up to 2.5% for the champion cells and 2.03% on average, marking an improvement by 10% compared to the 3D reference on mesoporous TiO₂. The effect is mainly due to a V _OC improvement by up to 70 mV on average, yielding a maximum V _OC of 1.18 V using different concentrations of phenethylammonium bromide. While these are among the highest reported V _OC values for Cs₂AgBiBr₆ solar cells, the effect is attributed to a change in recombination behavior within the full device and a better selectivity at the interface toward the hole transporting material (HTM). This explanation is supported by voltage-dependent external quantum efficiency, as well as photoelectron spectroscopy, revealing a better energy level alignment and thus a better hole-extraction and improved electron blocking at the HTM interface.