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Metal halide perovskite solar cells (PSCs) continue to improve their power conversion efficiency to over 25.5%, which is at the same level as silicon solar cells.

Methylammonium (MA)-free perovskite solar cells have the potential for better thermal stability than their MA-containing counterparts. However, the efficiency of MA-free perovskite solar cells lags behind due to inferior bulk quality. In this work, 4-methylphenethylammonium chloride (4M-PEACl) is added into a MA-free perovskite precursor, which results in greatly enhanced bulk quality. The perovskite crystal grains are significantly enlarged, and defects are suppressed by a factor of four upon the incorporation of an optimal concentration of 4M-PEACl. Quasi-2D perovskites are formed and passivate defects at the grain boundaries of the perovskite crystals. Furthermore, the perovskite surface chemistry is modified, resulting in surface energies more favorable for hole extraction. This facile approach leads to a steady state efficiency of 23.7% (24.2% in reverse scan, 23.0% in forward scan) for MA-free perovskite solar cells. The devices also show excellent light stability, retaining more than 93% of the initial efficiency after 1000 h of constant illumination in a nitrogen environment. In addition, a four-terminal mechanically stacked perovskite-silicon tandem solar cell with champion efficiency of 30.3% is obtained using this MA-free composition. The encapsulated tandem devices show excellent operational stability, retaining more than 98% of the initial performance after 42 day/night cycles in an ambient atmosphere.

The ternary strategy as a straightforward way for organic solar cells to improve the device performance attracts many interests in the field. The ternary strategy usually focuses on processing the ...

Structural defects are ubiquitous for polycrystalline perovskite films, compromising device performance and stability. Herein, a universal method is developed to overcome this issue by incorporating halide perovskite quantum dots (QDs) into perovskite polycrystalline films. CsPbBr3 QDs are deposited on four types of halide perovskite films (CsPbBr3, CsPbIBr2, CsPbBrI2, and MAPbI3) and the interactions are triggered by annealing. The ions in the CsPbBr3 QDs are released into the thin films to passivate defects, and concurrently the hydrophobic ligands of QDs self‐assemble on the film surfaces and grain boundaries to reduce the defect density and enhance the film stability. For all QD‐treated films, PL emission intensity and carrier lifetime are significantly improved, and surface morphology and composition uniformity are also optimized. Furthermore, after the QD treatment, light‐induced phase segregation and degradation in mixed‐halide perovskite films are suppressed, and the efficiency of mixed‐halide CsPbIBr2 solar cells is remarkably improved to over 11% from 8.7%. Overall, this work provides a general approach to achieving high‐quality halide perovskite films with suppressed phase segregation, reduced defects, and enhanced stability for optoelectronic applications., A universal approach is reported to fabricate perovskite films by incorporating inorganic CsPbBr3 quantum dots (QDs) into halide perovskite bulk films. Upon post‐annealing, the released elements from QDs compensate vacancies, and hydrophobic ligands on QDs passivate under‐charged Pb atoms and self‐assemble on surface. Therefore, the resulting films with reduced trap density, suppressed phase segregation, improved surface uniformity and enhanced stability are enabled.

We demonstrated an organic-inorganic composite as hole transport layer consisting of water-free PEDOT:PSS and tungsten oxide (WO3) nanoparticles, which enhanced the power conversion efficiency of normal-structure perovskite solar cells (PSCs). The PSC employing the WO3/PEDOT:PSS film as a hole transport layer exhibited better device stability and improved power conversion efficiency (PCE) with approximately 20% performance enhancement. The highest PCE obtained from WO3/PEDOT:PSS device was 15.1%, owing to simultaneous increments on short circuit current, open circuit voltage and fill factor. WO3 nanoparticles can fill out the pinholes of porous PEDOT:PSS layer, demonstrating a void-free and homogenous HTL surface. WO3/PEDOT:PSS composite demonstrated much higher charge conductivity and hole mobility than pristine PEDOT:PSS layer. The interface of perovskite absorber and WO3/PEDOT:PSS HTL also contained less defect density. The superior performance of WO3/PEDOT:PSS composite was attributed to the reduced current leakage, enhanced hole extraction characteristics, and less trap-assisted interfacial recombination via current density - voltage, electron microscopy (SEM, AFM and c-AFM), electrochemical impedance spectroscopy (EIS) and space-charge limited current–voltage (SCLC) measurements and analysis.

Organic solar cells (OSCs) based on fullerene acceptors demonstrated significant growth over the past two decades with power conversion efficiencies (PCE) exceeding 13%. However, the advent of non-fullerene (NF) acceptors with superior optoelectronic properties, tunable morphology, and absorption characteristics, have resulted in a scenario where the NF OSCs have demonstrated higher PCE of over 14% in single junction and over 17% in tandem OSCs incorporating NF OSCs which is relatively higher than conventional fullerene-based counterparts. In this review, recent progress and advancements made in the field of NF OSCs is discussed and its photovoltaic device performance ranging across several donor: acceptor (D/A) combinations is elaborated. The advantages of each NF materials in conjunction with the donor molecules is deliberated in the context of D/A blends correlating it to device performance. In addition, the challenges in the development and application of NF OSCs are also discussed, providing an overview for future developments.

Organic solar cells (OSCs) have again become a hot research topic in recent years. The record power conversion efficiency (PCE) of OSCs has boosted to over 17% in 2020. Apart from the high PCE, the stability of OSCs is also critical for their future applications and commercialization. Recently, many studies have proposed that burn-in degradation can be considered as an ineluctable barrier to long-term stable OSCs. However, there is still lack of studies to explain the detailed mechanism of this burn-in process. In this work, we first investigated the mechanism of the burn-in process in the high-efficiency PM6:N3-based nonfullerene OSCs. The PM6:N3-based device achieved a profound average PCE of 14.10% but also showed a significant performance loss after the burn-in degradation. Following characterizations such as dark

Semitransparent organic solar cells (STOSCs) are of great interest in both academic and industrial fields since they can be easily used as building windows to achieve solar power generation in building facades. However, many studies only focused on the optimisation of photocurrent generation and light transmission and ignored the colour-fidelity of devices. Meanwhile, many reported semitransparent organic solar cells require a very thin active layer around 100 nm which makes it difficult for them to be applied to large-scale window applications. Herein, we reported STOSCs with neutral color perception based on a PffBT4T-2OD:PC71BM thick active layer for the first time. We optimized the active layer thickness of the device from 300 nm to 120 nm to obtain the best performance. As a result, semitransparent devices showed a decreasing PCE and increasing AVT with the reduction of the active layer thickness. All semitransparent devices showed an excellent color rendering index above 90. The semitransparent device with an active layer thickness of 250 nm exhibits the best performance among all devices which corresponds to a considerable PCE of 6.60%, AVT of 16.3% and CRI of 90.7. This reveals that the PffBT4T-2OD:PC71BM based semitransparent devices with a thick active layer are suitable for application in building windows in terms of color perception and large-scale fabrication.

The ternary organic solar cell is a promising technology towards high power conversion efficiency. Although the efficiency has reached over 14% for ternary organic solar cells, the stability, as well as the degradation mechanism behind the ternary strategy, are still not well investigated. Burn-in photo-degradation, which is caused by continuous light illumination, can result in a significant performance drop at an initial stage for solar cells. COi8DFIC is a newly developed efficient non-fullerene acceptor material that exhibits strong near infrared range (NIR) light absorption. Herein, we present the first systematic research on the burn-in photo-degradation of a COi8DFIC based ternary organic solar cell with the active layer consisting of PTB7-Th:COi8DFIC:PC71BM blend and compared it with its corresponding binary organic solar cells. Both binary and ternary devices were exposed to continuous one-sun illumination for 5 hours. As a result, PTB7-Th:COi8DFIC based binary and ternary organic solar cells exhibit a similar degradation mechanism which is very different from the burn-in photo-degradation mechanism in PTB7-Th:PC71BM based binary organic solar cells. The burn-in photo-degradation in PTB7-Th:PC71BM binary organic solar cells is found to be dominated by induced non-radiative carrier recombination, poor energy transfer and low exciton dissociation. However, the burn-in photo-degradation in PTB7-Th:COi8DFIC based binary and ternary organic solar cells is found to be more related to the degradation-induced high shunt possibility.

Solution-processed organic solar cells (OSCs) have become a promising renewable energy technology in recent years. The fast initial degradation, which causes performance reduction at the initial stage for OSCs, needs to be understood and investigated thoroughly. In this work, for the first time, we have conducted a comparative study of light- and thermal-induced degradation during the burn-in process. As revealed in the estimation of Urbach energy, both light and thermal degradation created an increased energetic disorder. However, characterisation by steady-state photoluminescence (PL), time-resolved photoluminescence (TRPL) and capacitance–voltage (C–V) indicates that the mechanisms behind these two types of degradation are very different. The loss in light degradation was found to be more related to its degraded energy transfer ability, exciton dissociation ability and increased non-radiative recombination; whereas, the loss in thermal degradation was found to be more related to the reduced current extraction ability and increased leakage current.

This paper demonstrates an improved method to accurately extract the surface morphology of black silicon (BSi). The method is based on an automated Xe+ plasma focused ion beam (PFIB) and scanning electron microscope (SEM) tomography technique. A comprehensive new sample preparation method is described and shown to minimize the PFIB artifacts induced by both the top surface sample-PFIB interaction and the non-uniform material density. An optimized post-image processing procedure is also described that ensures the accuracy of the reconstructed 3D surface model. The application of these new methods is demonstrated by applying them to extract the surface topography of BSi formed by reactive ion etching (RIE) consisting of 2 µm tall needles. An area of 320 µm2 is investigated with a controlled slice thickness of 10 nm. The reconstructed 3D model allows the extraction of critical roughness characteristics, such as height distribution, correlation length, and surface enhancement ratio. Furthermore, it is demonstrated that the particular surface studied contains regions in which under-etching has resulted in overhanging structures, which would not have been identified with other surface topography techniques. Such overhanging structures can be present in a broad range of BSi surfaces, including BSi surfaces formed by RIE and metal catalyst chemical etching (MCCE). Without proper measurement, the un-detected overhangs would result in the underestimation of many critical surface characteristics, such as absolute surface area, electrochemical reactivity and light-trapping.

Organic solar cells are about to become a potential competitor to silicon solar cells. It is vital to understand the carrier recombination mechanism of organic solar cells to improve the device performance further. The diode ideality factor and carrier recombination resistance are the two commonly used parameters to describe the nongeminate, also called trap-assisted, recombination in solar cells. Herein, we demonstrated the relationship between these two parameters and derived an equation that can be used as a new method to estimate the carrier recombination resistance in organic solar cells. PBDB-T:ITIC-based nonfullerene organic solar cells, and PTB7:PC71BM and PffBT4T-2OD:PC71BM-based fullerene organic solar cells were fabricated to provide experimental proofs for our demonstration. A comparative study has been done between the fresh and aged PBDB-T:ITIC-based devices to further analyze the relationship between the carrier recombination resistance and the diode ideality factor.

Tin oxide (SnO2) has been reported as a promising electron transport layer (ETL) for planar heterojunction perovskite solar cells (PSCs). This work reports a low temperature solution-processed bila...

Inorganic cesium lead triiodide (CsPbI3) perovskite materials are becoming increasingly attractive for use in perovskite/silicon tandem solar cells, due to their almost ideal band gap energy (Eg) of about 1.7 eV. To be useful as photovoltaic absorbers, the CsPbI3 must form the cubic or black phase (α-CsPbI3). To do so at relatively low temperatures, hydroiodic acid (HI) is required as a solution additive. This paper demonstrates CsPbI3 perovskite solar cells with an efficiency of 6.44%, formed using a HI concentration of 36 μL/mL. This value is higher than the previous most commonly used HI additive concentration. Herein, by undertaking a systematic study of the HI concentration, we demonstrate that the structural, morphological, optical, and electrical properties of CsPbI3 solar cells, processed with this HI additive concentration, are superior.

Solution-processed organic solar cells (OSCs) have becoming a promising photovoltaic technology for a low-cost electricity generation. However, poor stability of OSCs is still a severe problem need to be understood and solved for future application. In this work, we conducted an air stability study for both fullerene and non-fullerene based OSCs. As a result, the degradation mechanism was found different for these two types of OSCs. The Urbach energy determined from the EQE measurement indicates that the air-degradation in fullerene based OSCs is mainly ascribed to its increased energetic disorder. Differently, the photoluminescence (PL) measurement implied that the air-degradation in non-fullerene based OSCs mainly results from the degraded charge dissociation and energy transfer ability. Therefore, different stability improving strategy will be needed for fullerene and non-fullerene based OSCs in future.

PEDOT:PSS has been widely used as a hole conductive polymer due to its high conductivity and transparency, which is ideal for thin film solar cell with large-scale printing processability. We demonstrated a simple way to enhance the efficiency and reproducibility of PEDOT:PSS-based normalstructure perovskite solar cells. Metal oxide MoO 3 layer has been thermal-evaporated onto PEDOT:PSS as a surface passivation layer. The PCE of perovskite solar cell has been enhanced by 18% after MoO 3 passivation and the short circuit current density (J sc ), open circuit voltage (V oc) and fill factor (FF) has been improved simultaneously. The performance enhancement of MoO 3 modified PSCs is attributed to the reduced current leakage, enhanced hole extraction characteristics, and mitigated the trap-assisted interfacial recombination.

Organic solar cells (OSCs) have reached their second golden age in recent two years with a boosted number of publications. Non-fullerene acceptor (NFA) materials have become a rising star in the field which are widely applied in organic solar cells because of their excellent optoelectronic properties, such as strong light-harvesting ability and tunable energy level. Unlike the low synthetic flexibility and high production cost of fullerene materials, NFAs exhibit flexible structures, and relatively low fabrication costs. Recently, the ternary strategy has become another hot research topic in the field, which introduces a third component into the binary host system for OSCs. The application of a ternary strategy can break the limits of light absorption brought by the host system, improve the morphology and energy level alignment for the active layer and thus improved the efficiency of organic solar cell devices. Benefiting from the advancement in both NFA and ternary strategy, the power conversion efficiency (PCE) of organic solar cell has exceeded over 17.5% to date. A comprehensive review of the recent progress in NFA based ternary OSCs (TOSCs) is needed in the field. Herein, this review mainly focuses on recent research on ternary organic solar cells using NFA materials during the last two years. Firstly, device physics and frequently used active materials in NFA based TOSCs are summarized and discussed. Then, the recent reported high-performance NFA based TOSCs are reviewed. Finally, the outlook and future research direction in the field are proposed. This review aims to provide an insight into NFA based TOSCs and help researchers to explore the full potential of OSCs.

Organic solar cells (OSCs) are considered to reach its second golden age with the profoundly improved power conversion efficiency (PCE) and device stability in recent years. The modification of the interface layer plays a significant role in achieving performance enhancement in OSCs. In this work, we reported for the use of the atomic layer deposited (ALD) ultrathin TiOx to modify the interface layer in OSCs. The modification with only 2 TiOx ALD cycles not only effectively passivates the interface between the ZnO electron transport layer (ETL) and the active layer, but also reduces the series resistance and improves the charge transport process in the device. We achieved an absolute 1% increase in PCE with enhanced device stability for modified OSCs. We also fabricated semitransparent OSCs by applying this interface modification strategy. The modification with 2 TiOx ALD cycles increases the electrical device performance without affecting the optical properties of the semitransparent device. An average PCE of 10.46% with an average visible transmittance (AVT) of 19.61% and color rendering index (CRI) close to 100 is demonstrated for the fabricated semitransparent device with the modification. The ALD assisted interface modification provides a straightforward way to realize high‐performance semitransparent OSCs. This article is protected by copyright. All rights reserved.

We demonstrated a high performance MA0.6FA0.4PbIxBr1-x mix-cation perovskite solar cell with thiocyanate assisted nucleation on low temperature processed SnO2 electron transport layer by gas-quenching deposition. The perovskite solar cell with thiocyanate additive exhibited enlarged grain size closed to 1 μm with improved power conversion efficiency (PCE) and better device stability. With the aid of thiocyanate additive, the champion cell has achieved the PCE of 19.64% with fill factor over 75%. Moreover, the SCN− assisted device showed considerably improved stability which retained 90% of its original PCE after degradation for 28 days, while the control device suffered 10% PCE loss after 14 days. Characterizations such as current density - voltage, electron microscopy (SEM, c-AFM, KPFM) and space-charge limited current–voltage (SCLC) measurements have been conducted for investigating the mechanism behind. The superior performance of SCN− assisted perovskite is owning to enlarged grain interiors as well as passivated grain boundaries, which attributed to the reduced current leakage, enhanced charge transport characteristics, and less trap-assisted interfacial recombination in the device.

Photovoltaic is one of the promising renewable sources of power to meet the future challenge of energy need. Organic and perovskite thin film solar cells are an emerging cost-effective photovoltaic technology because of low-cost manufacturing processing and their light weight. The main barrier of commercial use of organic and perovskite solar cells is the poor stability of devices. Encapsulation of these photovoltaic devices is one of the best ways to address this stability issue and enhance the device lifetime by employing materials and structures that possess high barrier performance for oxygen and moisture. The aim of this review paper is to find different encapsulation materials and techniques for perovskite and organic solar cells according to the present understanding of reliability issues. It discusses the available encapsulate materials and their utility in limiting chemicals, such as water vapour and oxygen penetration. It also covers the mechanisms of mechanical degradation within the individual layers and solar cell as a whole, and possible obstacles to their application in both organic and perovskite solar cells. The contemporary understanding of these degradation mechanisms, their interplay, and their initiating factors (both internal and external) are also discussed.

Hybrid halide perovskites are becoming increasingly popular due to their immense potential to be used as a low cost and easily processable solar cell technology. Interfacial engineering is believed to be one of the crucial ways to improve the device performance. In this work, we report the introduction of a small molecular interfacial layer 4,4’-(naphthalene-2,6-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (TPA-NAP-TPA) between the traditional hole transporting layer poly (3,4-ethylenedioxythiophene:polystyrene sulfonate) (PEDOT:PSS) and perovskite (Cs0.15FA0.85PbI3) active layer. Systematic investigations indicate that the incorporation of the small molecular interfacial layer improves the inverted device efficiency by 7% relative. The crystallinity and morphology of the perovskite formed on top of the PEDOT:PSS/TPA-NAP-TPA is favourable compared to the perovskite formed on top of pristine PEDOT:PSS layer. The improvement in the PCE is attributed to increased photocurrent generation. The devices containing the interfacial layer has also depicted improved quantum yield which is in line with the maximised average JSC. Furthermore, the devices with PEDOT:PSS/TPA-NAP-TPA interfacial layer retained 60% of their initial efficiency after 30 days, which is 30% higher than the devices with pristine PEDOT:PSS layer. Including interfacial layers such as TPA-NAP-TPA could be a viable technique in order to enhance the performance and stability of inverted structure perovskite solar cells.

Organic photovoltaics (OPV) has emerged as a promising renewable energy generation technology in the past decades. The thermal annealing effect on organic solar cells as one of the most widely used processing technologies have been substantially investigated. However, to the best of our knowledge, no research has investigated the changes in dielectric property and energetic disorder behind the thermal annealing processes. Herein, we conducted a systematic thermal annealing study for PffBT4T-2OD: PC71BM based organic solar cell and focused on the changes in dielectric property and energetic disorder. The characterisations such as J-V, EQE, PL, C–V, SCLC, AFM and TEM have been conducted for investigation. We systematically studied the annealing temperature up to 140 °C. It was found that devices annealed at 80 °C possess the most efficient exciton dissociation and charge extraction process and the highly suppressed the charge recombination which may be ascribed to its optimized interpenetrate morphology with optimized phase separation and domain size. The 80 °C annealed devices showed the largest dielectric constant and lowest capture coloumbic radius (Rc) among all devices which indicates that the optimized thermal annealing can tune the dielectric property of the device and induce more efficient charge separation. Moreover, we firstly estimated the annealing temperature-dependent Urbach energy. As results, all thermal annealed devices showed a reduced Urbach energy when compared to fresh devices, which proved that the thermal annealing process owns the ability to reduce the energetic disorder in the device.

Hybridization of Caesium and Formamidinium is considered as a promising approach to fabricate methylammonium-free perovskites for photovoltaic applications. Typically, CsxFA1-xPbI3 perovskite solar cells employ the normal device structure, which incorporates a high temperature processed rigid metal oxide layer as the electron transporting layer. This increases the cost of production and limits the use of Caesium-Formamidinium based perovskites for low temperature flexible substrates. In this study, we employed low temperature processed metal oxide free planar-heterojunction Caesium Formamidinium Lead Triiodide (Cs0.15FA0.85PbI3) perovskites in an inverted device structure and systematically investigated the role of post deposition annealing temperature on the film and device properties. The annealing temperature was varied from 130 °C to 170 °C. The film morphology and optical and charge extraction properties of devices is found to be highly dependent on the annealing temperature. The best average power conversion efficiency of 11.72% was obtained for 150 °C annealing temperature. These results show that determining the optimum post deposition annealing temperature is crucial to ensure successful charge extraction from the fabricated devices in order to achieve improved performance.