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Photovoltaic technology with low weight, high specific power in cold environments, and compatibility with flexible fabrication is highly desired for near‐space vehicles and polar region applications. Herein, we demonstrate efficient low‐temperature flexible perovskite solar cells by improving the interfacial contact between electron‐transport layer (ETL) and perovskite layer. We find that the adsorbed oxygen active sites and oxygen vacancies of flexible tin oxide (SnO2) ETL layer can be effectively decreased by incorporating a trace amount of titanium tetrachloride (TiCl4). The effective defects elimination at the interfacial increases the electron mobility of flexible SnO2 layer, regulates band alignment at the perovskite/SnO2 interface, induces larger perovskite crystal growth, and improves charge collection efficiency in a complete solar cell. Correspondingly, the improved interfacial contact transforms into high‐performance solar cells under one‐sun illumination (AM 1.5G) with efficiencies up to 23.7 % at 218 K, which might open up a new era of application of this emerging flexible photovoltaic technology to low‐temperature environments such as near‐space and polar regions. [ABSTRACT FROM AUTHOR]

All‐polymer solar cells (all‐PSCs) have promising potential for industrial production due to their superior stability. Recently, the widespread application of the polymerized small molecule acceptor (PSMA) has led to a surge in the efficiency of all‐PSCs. However, the high efficiencies of these devices generally rely on the use of the highly volatile solvent, chloroform (CF). Furthermore, the molecular weights of PSMA are lower than polymer donors, yet their crystallinity is weaker than typical small molecules, making most PSMA‐based all‐PSCs suffer from low electron mobility. To improve device performance and facilitate large scale production of all‐PSCs, it is necessary to enhance electron mobility and avoid the use of CF. This paper investigates the use of sequential processing (SqP) for active layer preparation using toluene as the solvent to address these issues. This work reports 18.1% efficient all‐PSC devices, which is the highest efficiency of all‐PSCs prepared using non‐halogen solvents. This work systematically compares the conventional blend‐casting method with the SqP method using PM6 as the donor and PY‐V‐γ and PJ1‐γ as the acceptors, and compares the performance of binary and ternary blends in both methods. Finally, this work measures the device stability and finds that SqP can significantly improve the photostability of the device. [ABSTRACT FROM AUTHOR]

Organic solar cells (OSCs) have gained increasing attention. Among the various directions in OSCs, all-polymer solar cells (all-PSCs) have emerged as a highly promising and currently active research area due to their excellent film formation properties, mechanical properties, and thermal stabilities. However, most of the high-efficiency all-PSCs are processed from chloroform with an active layer thickness of ~100 nm. In order to meet the requirements for industrialization, a thicker active layer processed from low-vapor pressure solvents (preferentially a hydrocarbon solvent) is strongly desired. Herein, we employ toluene (a hydrocarbon solvent with a much higher boiling point than chloroform) and a method known as sequential processing (SqP) to mitigate the rapid decline in efficiency with increasing film thickness. We show that SqP enables a more favorable vertical phase segregation that leads to less trap-assisted recombination and enhanced charge extraction and lifetime than blend-cast devices at higher film thicknesses. [ABSTRACT FROM AUTHOR]

All-polymer solar cells (all-PSCs) are organic solar cells in which both the electron donor and the acceptor are polymers and are considered more promising in large-scale production. Thanks to the polymerizing small molecule acceptor strategy, the power conversion efficiency of all-PSCs has ushered in a leap in recent years. However, due to the electrical properties of polymerized small-molecule acceptors (PSMAs), the FF of the devices is generally not high. The typical electron transport material widely used in these devices is PNDIT-F3N, and it is a common strategy to improve the device fill factor (FF) through interface engineering. This work improves the efficiency of all-polymer solar cells through interfacial layer engineering. Using PDINN as the electron transport layer, we boost the FF of the devices from 69.21% to 72.05% and the power conversion efficiency (PCE) from 15.47% to 16.41%. This is the highest efficiency for a PY-IT-based binary all-polymer solar cell. This improvement is demonstrated in different all-polymer material systems. [ABSTRACT FROM AUTHOR]

All-polymer solar cells (All-PSCs), whose electron donor and acceptors are both polymeric materials, have attracted great research attention in the past few years. However, most all-PSC devices with top-of-the-line efficiencies are processed from chloroform. In this work, we apply the sequential processing (SqP) method to fabricate All-PSCs from an aromatic hydrocarbon solvent, toluene, and obtain efficiencies up to 17.0%. By conducting a series of characterizations on our films and devices, we demonstrate that the preparation of SqP devices using toluene can effectively reduce carrier recombination, enhance carrier mobility and promote the fill factor of the device. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) perovskite formed by introducing various organic spacer cations into 3D perovskite is considered to be one of the most effective methods to improve the humidity stability of perovskite materials. In order to solve the phase inhomogeneity and phase distribution nonuniformity of two-dimensional perovskites, additive engineering technique is widely used during their fabrication processes. Although many additives are proved to be effective in improving the quality of perovskite films, the mechanism of additive engineering has not been fully understood. In our work, we prepare 2D Ruddlesden–Popper perovskites based on 4-bromophenylethylammonium (BPEA) using a new additive of ionic liquids MAAc (methylammonium acetate). The (BPEA)2(MA)4Pb5I16 perovskite prepared with the assistance of MAAc exhibits a stable photoelectric conversion efficiency (PCE) of 8.47%, which is much higher than the one without MAAc additive (4.79%). Besides a nearly tenfold increase in electron mobility, the unencapsulated (BPEA)2(MA)4Pb5I16-based device with MAAc additive remains 88% of its initial efficiency after 960 h exposure to air with a humidity of 20 ± 5% at room temperature, while the device without additive decreases to 63% of its initial efficiency. Meanwhile, the interactions between PbI2 and MAAc at different temperatures and molar ratios are investigated and the formation mechanism of 2D perovskites in the presence of MAAc is proposed. It is found that an intermediate perovskite with distorted [PbI6−xAcx]4− octahedron is formed with the addition of MAAc, making the quality and photoelectric properties of the resultant films greatly enhanced. [ABSTRACT FROM AUTHOR]

Constructing tandem junction devices consisting of a bottom cell based on prevailing solar cell techniques such as silicon (Si) or Cu(In,Ga)(Se,S)2 (CIGS) combined with a perovskite top cell is one effective approach to improve photovoltaic device performance. An intermediate transparent conducting layer as one component of the tunnel junction connecting the two single devices, at the same time serving as inorganic hole transport material for the perovskite solar cell is one of the key components to realize a perovskite-CIGSe tandem structure. In this contribution, we describe the deposition of p-type Cu2O films at room temperature by magnetron sputtering using nitrogen doping to form a homogenous layer with high transparency and good conductivity, and the modeling of a monolithic perovskite-CIGSe tandem solar cell utilizing this layer. We applied the in-house software RefDex to illustrate the impact of Cu2O on the performance of a tandem device, and calculated the reflection, transmission, and absorption. [ABSTRACT FROM AUTHOR]

Vacuum free, solution based routes to the preparation of chalcopyrite absorbers for solar cells promise options in device design and manufacturing that are not provided by the standard vacuum based approaches. In order to fully exploit these options, the precursor should contain neither nanoparticles nor hazardous chemicals, and it should be stable under ambient conditions. In this contribution we report on CuIn(S,Se)2 thin film preparation based on spin coating of an air stable molecular ink containing metal chlorides and thiourea in organic solvents. Several key parameters directly influencing the performance of the resulting solar cells have been identified. Wetting of the glass/Mo substrate has been adjusted by varying the concentration of ethylene glycol butyl ether in the ink. Before annealing in Ar/Se at atmospheric pressure, several cycles of ink deposition and drying can be used to increase the thickness of the precursor stack. Careful balancing of ink concentration, number of precursor deposition cycles, and annealing temperature profile will transform the multi-layer precursor into a sufficiently thick, continuous, large grained film as required for high quantum efficiency, and good red response of the cells. These optimizations aimed at high photo current have already led to an efficiency of 9.5%. [ABSTRACT FROM AUTHOR]

In order to surpass the theoretical limitation defined by the Shockley–Queisser equation for photovoltaic solar cells, multijunction devices are needed. Monolithic perovskite‐Cu(In, Ga)(Se, S)2 (CIGSe) tandem solar cells have recently become a hot research topic in photovoltaics because of the emergence of perovskite solar cells with high power conversion efficiency and the development of thin film chalcopyrite CIGSe solar cells with tunable bandgap and low cost manufacturing processes. In this review, some p‐type wide bandgap semiconductors are investigated as intermediate inorganic hole transport materials (IIHTM) and components of a tunnel junction in monolithic perovskite‐CIGSe tandem solar cells, which meet the requirements of band alignment and low‐temperature deposition process. The authors focus on designing a tandem configuration including band alignment, current matching, and optical management, describing some potential candidates of IIHTM owing to their successful implementation in single junction perovskite solar cells and the possibility of application in intermediate layers for tandem devices. Recent progress in the development of inorganic hole conductors is highlighted, and also some of the authors' work on IIHTM and their applications are presented. Finally, future research directions for IIHTM layers and monolithic perovskite‐CIGSe tandem solar cells are presented, with an aim to achieve higher photovoltaic performance than current devices. Potential candidates for inorganic intermediate layers with wide bandgaps as hole transport materials and one component of tunnel junction for the monolithic perovskite‐CIGSe tandem solar cells are reviewed. Several requirements for the fabrication of monolithic tandem devices are discussed in order to facilitate higher photovoltaic performance than in current devices. [ABSTRACT FROM AUTHOR]

In conventional Cu(In,Ga)Se 2 (CIGSe) solar cells a chemical bath deposited CdS thin film is used as a buffer layer. However, it is desired to replace CdS due to the toxicity of cadmium and the rather narrow bandgap energy of CdS. Zn(O,S) is considered to be one of the most attractive candidates as an alternative, non-toxic buffer layer with a larger bandgap. This paper aims to compare the properties of the CdS/CIGSe and the Zn(O,S)/CIGSe interfaces depending on the absorber composition and the application of an RbF post deposition treatment (PDT). Synchrotron-based hard X-ray photoelectron spectroscopy revealed a strong correlation of Cd diffusion and concentration of V Cu in CIGSe before the PDT. Additionally, the RbF-PDT enhanced the Cd diffusion into the CIGSe. On the other hand, it was found that Zn atoms are not as easily incorporated into the CIGSe as Cd atoms. As a result, we consider the formation of donor-like Zn Cu + defects at the interface to be less likely than the formation of Cd Cu + defects. Moreover, we observed that the Zn(O,S)/CIGSe interface is less sensitive to changes of the CIGSe composition and to the RbF-PDT compared to the CdS/CIGSe interface. • Cd diffusion into CIGSe surface depends on the Cu concentration before RbF-PDT. •RbF-PDT enhances the Cd diffusion into CIGSe surface. •Zn atoms are not as easily incorporated into the CIGSe as Cd atoms. •Formation of Zn Cu + defects at the interface is less likely than the Cd Cu + defects. •Zn(O,S)/CIGSe interface is less affected by the RbF-PDT compared to the CdS/CIGSe. [ABSTRACT FROM AUTHOR]

Mn-doping into CdS quantum dots (QDs) has been demonstrated a useful way to enhance the power conversion efficiency (PCE) of quantum dot sensitized solar cells (QDSCs), the detailed systematic study is needed to get a better fundamental understanding. This work focuses on the study of the effects of Mn dopant on light harvesting, charge transfer, and charge collection of the solar cells. The results indicate that the Mn-doping into CdS QDs increases the light absorbance and extends the light absorption range, which results in the enhancement of the photo-generated current density. In addition, both the electron transport rate and the electron diffusion length are also increased with the introduction of Mn dopant. So the charge collection efficiency ( η cc ) of the solar cell increases from 89.9% for CdS sample to 96.7% for Mn/CdS sample. As a result, the PCE of Mn/CdS QDSC reaches 3.29%, which is much higher than that of CdS QDSC (2.01%). [ABSTRACT FROM AUTHOR]