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Perovskite solar cells (PSCs) have gained tremendous attention owing to their promising photovoltaic performance, surpassing all the alternative technologies based on solution‐processed materials. PSCs displaying record efficiencies contain hole transporting material (HTM) and gold back contact, which are too expensive for large‐scale deployment. Although the HTM‐free PSCs have been reported, a few can be used in tandem configuration, an architecture that is warranted to commercialize PSCs. This work presents, to the best of our knowledge, the first HTM‐free and Au‐free PSCs that are semi‐transparent in the IR region (desired for tandem cells) with an efficiency of 8.3 %. We systematically investigate the effect of varying the thickness of active and charge conducting layers on the photovoltaic performance of PSCs. Besides, semitransparency, another advantage of the scaffold is its simplicity: a fully printable mesoporous structure consisting of a TiO2 layer (400 nm), Al2O3 as a separator layer (500 nm) and tin‐doped indium oxide (ITO) layer (5 μm), rendering our work highly pertinent for upscaling and large‐scale applications. [ABSTRACT FROM AUTHOR]

Hole transport materials (HTM) are an important component in perovskite solar cells (PSC). Despite a multitude of HTMs developed in recent years, only few of them lead to solar cells with efficiencies over 20%. Therefore, it is still a challenge to develop high‐performing HTMs, which have ideal energy levels of the frontier orbitals, are highly efficient in transporting charges, and stabilize the solar cell at the same time. In this work, the development of a structurally novel molecular HTM, CPDA 1, is described which is based on a common cyclopentadiene core and can be efficiently and inexpensively synthesized from readily available starting materials, which is important for future realization of low‐cost photovoltaics on larger scale. Due to excellent optoelectronic, thermal, and transport properties, CPDA 1 not only meets the envisioned properties by reaching high efficiencies of 23.1%, which is among the highest reported to date, but also contributes to a respectable long‐term stability of the PSCs. [ABSTRACT FROM AUTHOR]

Dye‐sensitized solar cells (DSCs) based on copper(II/I) redox mediators have recently achieved notable performance progress through tailoring the ligand structure of the copper complexes, exploiting cosensitization, and introducing an advanced device structure. In order to further improve the power conversion efficiency (PCE), it is imperative to develop wide spectral‐response photosensitizers compatible with the copper(II/I) redox mediators while attaining a high Voc. Herein, a blue photosensitizer coded R7 is reported, which is purposely designed for highly efficient DSCs with copper‐based electrolytes. R7 features a strong electron‐donating segment of 9,19‐dihydrobenzo[1′,10′ ]phenanthro[3′,4′:4,5]thieno[3,2‐b]benzo[1,10]phenanthro[3,4‐d]thiophene conjugated with a bulky auxiliary donor N‐(2,4′‐bis(hexyloxy)‐[1,1′‐biphenyl]‐4‐yl)‐2,4′‐bis(hexyloxy)‐N‐methyl‐[1,1′‐biphenyl]‐4‐amine and the electron acceptor 4‐(7‐ethynylbenzo[c][1,2,5]thiadiazol‐4‐yl)benzoic acid. The blue dye R7 with bulkier auxiliary donor moiety in the DSC largely outperforms the reference dye R6, which has a smaller bis(4‐(hexyloxy)phenyl)amine donor unit. Transient absorption spectroscopy and electrochemical impedance spectroscopy measurements show that the R7 based DSC has a higher charge separation yield, a higher charge collection efficiency, and lower charge recombination with the copper electrolyte than the R6 based counterpart. A cosensitized system of R7 and Y123 for the DSC presents an outstanding PCE of 12.7% and retains 90% of its initial value after 1000 h of light soaking under 1 sun at 45 °C. [ABSTRACT FROM AUTHOR]

Dye‐sensitized solar cells (DSSCs) based on CuII/I bipyridyl or phenanthroline complexes as redox shuttles have achieved very high open‐circuit voltages (VOC, more than 1 V). However, their short‐circuit photocurrent density (JSC) has remained modest. Increasing the JSC is expected to extend the spectral response of sensitizers to the red or NIR region while maintaining efficient electron injection in the mesoscopic TiO2 film and fast regeneration by the CuI complex. Herein, we report two new D‐A‐π‐A‐featured sensitizers termed HY63 and HY64, which employ benzothiadiazole (BT) or phenanthrene‐fused‐quinoxaline (PFQ), respectively, as the auxiliary electron‐withdrawing acceptor moiety. Despite their very similar energy levels and absorption onsets, HY64‐based DSSCs outperform their HY63 counterparts, achieving a power conversion efficiency (PCE) of 12.5 %. PFQ is superior to BT in reducing charge recombination resulting in the near‐quantitative collection of photogenerated charge carriers. [ABSTRACT FROM AUTHOR]

A series of two‐dimensionally expanded azulene‐core‐based π systems have been synthesized with different alkyl chain lengths in the alkoxy moieties connected to the partially oxygen‐bridged triarylamine skeletons. The thermal, photophysical, and electronic properties of each compound were evaluated to determine the influence of the alkyl chain length on their effectiveness as hole‐transporting materials (HTMs) in perovskite solar cells (PSCs). All the synthesized molecules showed promising material properties, including high solubility, the formation of flat and amorphous films, and optimal alignment of energy levels with perovskites. In particular, the derivatives with methyl and n‐butyl in the side chains retained amorphous stability up to 233 and 159 °C, respectively. Such short alkoxy chains also resulted in improved electrical device properties. The PSC device fabricated with the HTM with n‐butyl side chains showed the best performance with a power conversion efficiency of 18.9 %, which compares favorably with that of spiro‐OMeTAD‐based PSCs (spiro‐OMeTAD=2,2′,7,7′‐tetrakis[N,N‐bis(p‐methoxyphenyl)amino]‐9,9′‐spirobifluorene). [ABSTRACT FROM AUTHOR]

High photovoltage in perovskite solar cells (PSCs) can be achieved by designing new hole transporting materials (HTMs) with relatively deeper energy levels of the highest occupied molecular orbital (HOMO). Here, we report on the synthesis of a new heteroacene‐based HTM (HTM‐1) and demonstrate its potential in the fabrication of FAPbBr3 [FA = CH(NH2)2] PSCs yielding VOC as high as 1.55 V, a record value for this light harvester. The energetic position of the frontier orbitals of HTM‐1 was estimated using electrochemical measurements, and the charge transport across the interfaces was studied using steady‐state and time‐resolved photoluminescence. When spiro‐OMeTAD (HOMO = –5.1 eV) is replaced with HTM‐1 (HOMO = –5.3 eV), the VOC increases from 1.51 to 1.55 V, whereas the JSC value decreases from 7.0 to 5.7 mA cm–2. The similar trade‐off between JSC and VOC is observed for efficient iodide‐based PSCs, suggesting that there is a critical energy level for the HOMO below which overall photovoltaic performance will suffer. After probing at a maximum power point under full‐sun illumination at 60 °C for a duration of 120 h, the FAPbBr3 PSCs based on HTM‐1 retained ≈ 95 % of their initial efficiency, which demonstrates their robust operational stability. A new heteroacene‐based hole transporting material (HTM) was designed and used in the fabrication of FAPbBr3 [FA = CH(NH2)2] robust solar cells yielding a VOC of 1.55 V, a record value for this light harvester. A trade‐off between JSC and VOC was observed when the HOMO level was lowered, suggesting that there is a critical energy level for the HOMO, below which overall photovoltaic performance will suffer. [ABSTRACT FROM AUTHOR]

The synthesis, characterization, and photovoltaic performance of a series of indacenodithiophene (IDT)‐based D‐π‐A organic dyes with varying electron‐accepting units is presented. By control of the electron affinity, perfectly matching energy levels were achieved with a copper(I/II)‐based redox electrolyte, reaching a high open‐circuit voltage (>1.1 V) while harvesting a large fraction of solar photons at the same time. Besides achieving high power conversion efficiencies (PCEs) for dye‐sensitized solar cells (DSCs), that is, 11.2 % under standard AM 1.5 G sunlight, and 28.4 % under a 1000 lux fluorescent light tube, this work provides a possible method for the design and fabrication of low‐cost highly efficient DSCs. A series of indacenodithiophene (IDT)‐based D‐π‐A organic dyes with varying electron‐accepting units were synthesized, characterized, and the photovoltaic performance investigated. By control of the electron affinity, perfectly matching energy levels were achieved with a copper(I/II)‐based redox electrolyte, achieving efficient dye‐sensitized solar cells with a power conversion efficiency of up to 11.2% and high open‐circuit voltages of over 1.1 V. [ABSTRACT FROM AUTHOR]

Abstract: Passivation of electronic defects is an effective strategy to boost the performance and operational stability of perovskite solar cells (PSCs). Identifying molecular materials that achieve this purpose is a key target of current research efforts. Here, adamantane (AD) and 1‐adamantylamine (ADA) are introduced as molecular modulators to abate electronic defects present within the bulk and at the perovskite–hole conductor interface. To this effect, the modulator is added either into the antisolvent (AS) to precipitate it together with the perovskite (AS method) or they are spin coated (SC) onto its surface (SC method). Time‐resolved photoluminescence measurements show substantially longer lifetimes for perovskite films treated with AD and ADA compared to the reference sample. In line with this observation, it is found that the presence of AD and ADA molecules at the interface between the perovskite film and the hole conductor increases all photovoltaic metrics, in particular the open circuit photovoltage (V oc) as well as the operational stability of the PSC. [ABSTRACT FROM AUTHOR]

Abstract: The electronic processes occurring within the perovskite solar cells (PSCs) are strongly influenced by the nature of the organic A cations present within the inorganic framework. In this study, the impact of FA (CH(NH2)2+) and Cs+ cations on the intrinsic and interfacial properties in the FAPbBr3 and CsPbBr3 PSCs is investigated. The analysis of current density (JSC) and photovoltage (VOC) as a function of illumination intensity establishes that the interfacial charge transport is more rapid in FAPbBr3 devices. Small perturbation measurements including intensity modulated photocurrent and photovoltage spectroscopy are applied to explore the resistive and capacitive elements. Furthermore, electrochemical impedance spectroscopy measurements are found to correlate well with the photovoltaic characteristics of FAPbBr3 and CsPbBr3 PSCs. Overall, the in‐depth analysis of various phenomena occurring within the bromide PSCs allows to underline the working principle, which provides a key to optimize the device performance. The present protocol is not only valid for PSCs but can also be extended to devices based on alternative light harvesters. [ABSTRACT FROM AUTHOR]

The surge of the power conversion efficiency of metal halide lead perovskite solar cells comes with concerns, such as the long-term ecotoxicity of lead compounds, their sensitivity toward moisture and oxygen, or the scarcity of some of their components. Most perovskite solar cells still suffer from serious stability problems when measured under real working conditions (maximum power point tracking at 60°C). In the long run, stability will certainly decide on the fate of CH3NH3PbI3 and related lead perovskites for their use in photovoltaic modules. Herein, we show an effective and inexpensive strategy to perform ageing of perovskite solar cells under maximum power point tracking. For the first time, we analyze the issue of power extraction from solar cells exhibiting hysteresis. We show that a standard tracking algorithm such as perturb and observe fails to converge to the maximum power point of the solar cell if it exhibits j( V) hysteresis, and we present an effective strategy to stabilize the algorithm. We show that enforcing oscillations in forward bias can boost the mean power output of some perovskite solar cells by more than 10%, in contrast to a reference crystalline silicon solar cell. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Charge carrier dynamics in organolead iodide perovskites is analyzed by employing time-resolved photoluminescence spectroscopy with several ps time resolution. The measurements performed by varying photoexcitation intensity over five orders of magnitude enable separation of photoluminescence components related to geminate and nongeminate charge carrier recombination and to address the dynamics of an isolated geminate electron-hole pair. Geminate recombination dominates at low excitation fluence and determines the initial photoluminescence decay. This decay component is remarkably independent of the material structure and experimental conditions. It is demonstrated that dependences of the geminate and nongeminate radiative recombination components on excitation intensity, repetition rate, and temperature, are hardly compatible with carrier trapping and exciton dissociation models. On the basis of semiclassical and quantum mechanical numerical calculation results, it is argued that the fast photoluminescence decay originates from gradual spatial separation of photogenerated weakly bound geminate charge pairs. [ABSTRACT FROM AUTHOR]

Understanding the relationship between the growth and local emission of hybrid perovskite structures and the performance of the devices based on them demands attention. This study investigates the local structural and emission features of CH3NH3PbI3, CH3NH3PbBr3, and CH(NH2)2PbBr3 perovskite films deposited under different yet optimized conditions using X-ray scattering and cathodoluminescence spectroscopy, respectively. X-ray scattering shows that a CH3NH3PbI3 film involving spin coating of CH3NH3I instead of dipping is composed of perovskite structures exhibiting a preferred orientation with [202] direction perpendicular to the surface plane. The device based on the CH3NH3PbI3 film composed of oriented crystals yields a relatively higher photovoltage. In the case of CH3NH3PbBr3, while the crystallinity decreases when the HBr solution is used in a single-step method, the photovoltage enhancement from 1.1 to 1.46 V seems largely stemming from the morphological improvements, i.e., a better connection between the crystallites due to a higher nucleation density. Furthermore, a high photovoltage of 1.47 V obtained from CH(NH2)2PbBr3 devices could be attributed to the formation of perovskite films displaying uniform cathodoluminescence emission. The comparative analysis of the local structural, morphological, and emission characteristics of the different perovskite films supports the higher photovoltage yielded by the relatively better performing devices. [ABSTRACT FROM AUTHOR]

Three novel hole-transporting materials (HTMs) using the 4-methoxytriphenylamine (MeOTPA) core were designed and synthesized. The energy levels of the HTMs were tuned to match the perovskite energy levels by introducing symmetrical electron-donating groups linked with olefinic bonds as the π bridge. The methylammonium lead triiodide (MAPbI3) perovskite solar cells based on the new HTM Z34 (see main text for structure) exhibited a remarkable overall power conversion efficiency (PCE) of 16.1 % without any dopants or additives, which is comparable to 16.7 % obtained by a p-doped 2,2′,7,7′-tetrakis-( N, N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD)-based device fabricated under the same conditions. Importantly, the devices based on the three new HTMs show relatively improved stability compared to devices based on spiro-OMeTAD when aged under ambient air containing 30 % relative humidity in the dark. [ABSTRACT FROM AUTHOR]

A triphENylamine based molecular “butterfly” is developed as dopant ‐ free hole ‐ transport material for perovskite solar cells exhibiting excellENt power conversion efficiENcy of 16.3% which is comparable to the state ‐ of ‐ the ‐ art doped 2,2′,7,7′ ‐ tetrakis(N,N′ ‐ di ‐ p ‐ methoxy ‐ phENylamine) ‐ 9,9′ ‐ spirobifluorENe (spiro ‐ OMeTAD). Moreover, the device is much more stable than that of spiro ‐ OMeTAD based device under light irradiation. [ABSTRACT FROM AUTHOR]

We developed a new donor-π-acceptor-type hole-transport material (HTMs) incorporating S, N-heteropentacene as π-spacer, triarylamine as donor, and dicyanovinylene as acceptor. In addition to appropriate frontier molecular orbital energies, the new HTM showed high photo absorptivity in the visible region. Without the use of p-dopants, solution-processed mixed perovskite devices using the HTM achieved power conversion efficiencies of up to 16.9% and high photocurrents of up to 22.2 mA cm−2. These results demonstrate that heteroacene can be an excellent building block to prepare alternative HTMs for perovskite solar cells and hold promise for further advancement through fine-tuning the molecular structure. [ABSTRACT FROM AUTHOR]

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

One of the most challenging obstacles to commercialization of perovskite solar cells (PSCs) is their instability toward environmental conditions. An emerging solution to overcome these challenges relies on graphene‐based composites, in particular, solution‐processable reduced graphene oxide (rGO), whose high electrical and thermal conductivity, along with beneficial passivation effects, display multifaceted utility in PSCs. This review provides a brief summary of functions of rGO in different PSC architectures, from a potential replacement for transparent conductive oxides, through usage in electron‐transporting and perovskite layers, with the particular emphasis on its application as a hole‐transporting material and a spacer layer. Despite ongoing research challenges, the synergy between rGO and PSCs promises to facilitate the future applications of efficient and stable PSCs. Reduced graphene oxide has a multidimensional utility in perovskite solar cells, and it is of particular interest in improving their long‐term stability as an alternative hole‐transporting material, passivating agent, and a spacer layer. A brief overview of the present functions and future challenges for the applications of reduced graphene oxide in perovskite solar cells is provided. [ABSTRACT FROM AUTHOR]