Chen Weijie

A simple and effective strategy of dual-slot-die sequential processing (DSDS) is developed. Highly efficient nonhalogenated organic solar cells are fabricated by slot-die coating by the DSDS strategy without additives and complex post-treatments.

Abstract

Organic solar cells (OSCs) are promising candidates for next-generation photovoltaic technologies, with their power conversion efficiencies (PCEs) reaching 19%. However, the typically used spin-coating method, toxic halogenated processing solvents, and the conventional bulk-heterojunction (BHJ), which causes excessive charge recombination, hamper the commercialization and further efficiency promotion of OSCs. Here, a simple but effective dual-slot-die sequential processing (DSDS) strategy is proposed to address the above issues by achieving a continuous solution supply, avoiding the solubility limit of the nonhalogen solvents, and creating a graded-BHJ morphology. As a result, an excellent PCE of 17.07% is obtained with the device processed with o-xylene in an open-air environment with no post-treatment required, while a PCE of over 14% is preserved in a wide range of active-layer thickness. The unique film-formation mechanism is further identified during the DSDS processing, which suggests the formation of the graded-BHJ morphology by the mutual diffusion between the donor and acceptor and the subsequent progressive aggregation. The graded-BHJ structure leads to improved charge transport, inhibited charge recombination, and thus an excellent PCE. Therefore, the newly developed DSDS approach can effectively contribute to the realm of high-efficiency and eco-friendly OSCs, which can also possibly be generalized to other organic photoelectric devices.

Tailored P3CT-BA polyelectrolyte is demonstrated to be an efficient hole-transporting layer for large-area 2D perovskite solar cells with a power conversion efficiency approaching 18 %, and large-area (2×3 cm², 5×5 cm²) 2D perovskite devices are also reported with an impressive efficiency of 14.81 % and 11.13 %, respectively.

Abstract

Ruddlesden–Popper phase 2D perovskite solar cells (PSCs) exhibit improved lifetime while still facing challenges such as phase alignment and up-scaling to module-level devices. Herein, polyelectrolytes are explored to tackle this issue. The contact between perovskite and hole-transport layer (HTL) is important for decreasing interfacial non-radiative recombination and scalable fabrication of uniform 2D perovskite films. Through exploring compatible butylamine cations, we first demonstrate poly(3-(4-carboxybutyl)thiophene-2,5-diyl)-butylamine (P3CT-BA) as an efficient HTL for 2D PSCs due to its great hydrophilicity, relatively high hole mobility and uniform surface. More importantly, the tailored P3CT-BA has an anchoring effect and acts as the buried passivator for 2D perovskites. Consequently, a best efficiency approaching 18 % was achieved and we further first report large-area (2×3 cm², 5×5 cm²) 2D perovskite minimodules with an impressive efficiency of 14.81 % and 11.13 %, respectively.

Nature Energy, Published online: 13 June 2022; doi:10.1038/s41560-022-01046-1

Herein, glycine halides (Gly-X: X = Cl, Br and I) are designed to passivate CsPbI₂Br. Experimental and calculated results prove that Gly-X-based 2D perovskite is formed and located at CsPbI₂Br grain boundaries. The Gly-I forms strong interaction with 3D perovskite to suppress ion migration. Thus, an efficiency of 17.26% is obtained with high open-circuit voltage (1.33 V) and high illumination stability.

Abstract

CsPbI₂Br perovskite is known for its advantages over its organic-inorganic hybrid counterpart including better thermal stability and appropriate bandgap for the front sub-cell of tandem solar cell. However, its lower-than-satisfactory efficiency, problematic phase stability and sensitivity to moisture hinder its further advancement. Here, three kinds of glycine halides (Gly-X: X = Cl, Br, and I) are strategically deigned to improve the performance of CsPbI₂Br perovskite solar cells (PSCs). Systematic experimental and calculated results prove that a 2D/3D hybrid structure is formed, wherein the Gly-X-based 2D perovskite is mainly located at the CsPbI₂Br grain boundaries, and the A-sites of the 2D perovskite form strong bonds with the 3D perovskite to suppress ion migration by increasing its activation energy. As a result, a power conversion efficiency (PCE) of 17.26% was obtained with an open-circuit voltage (V _OC) of 1.33 V, which is among the best PCE values for the CsPbI₂Br PSCs. In addition, the efficiency of encapsulated device decrease only by 14.1% after 340 h continuous illumination in ambient conditions, representing one of the most-stable inorganic PSCs reported so far. This work provides important insights into designing passivating agents to address the issue of phase segregation for the development of highly stable perovskite optoelectronic devices.

A TOPCon c-Si cell produced on a production line is used as the bottom cell of a tandem device, and a top cell featuring solution-processed perovskite films is used to form the tandem device. The c-Si cell features a rough damage etched, but untextured front surface from the wafering processes. 27.6% efficiency is achieved for a monolithic perovskite/c-Si tandem device.

Abstract

The tandem cell structure is the most promising solution for the next generation photovoltaic technology to overcome the single-junction Shockley–Queisser limit. The fabrication of a perovskite/c-Si monolithic tandem device has not yet been demonstrated on a c-Si bottom cell produced from an industrial production line. Here, a c-Si cell with a tunneling oxide passivating contact (TOPCon) structure produced on a production line as the bottom cell of a tandem device, and a top cell featuring solution-processed perovskite films to form the tandem device are used. The c-Si cell features a rough damage etched, but untextured front surface from the wafering processes. To combat the challenge of rough surfaces, several strategies to avoid shunt paths across carrier transport layers, absorber layers, and their interfaces are implemented. Moreover, the origin of reflection loss on this planar structure is investigated and the reflection loss is managed to below 4 mA cm⁻². In addition, the source of the voltage loss from the TOPCon bottom cell is identified and the device structure is redesigned to be suitable for tandem applications while still using mass production feasible fabrication methods. Overall, 27.6% efficiency is achieved for a monolithic perovskite/c-Si tandem device, with significant potential for future improvements.

This work proposes an innovative fabrication method for perovskite-based tandem photovoltaics. The lamination process recrystallizes the perovskite thin film and thereby unites two independent device half-stacks at elevated temperatures and pressures. Notably, the first prototypes of laminated monolithic perovskite/silicon already demonstrate stable power conversion efficiencies up to 20%.

Abstract

Perovskite/silicon tandem photovoltaics have attracted enormous attention in science and technology over recent years. In order to improve the performance and stability of the technology, new materials and processes need to be investigated. However, the established sequential layer deposition methods severely limit the choice of materials and accessible device architectures. In response, a novel lamination process that increases the degree of freedom in processing the top perovskite solar cell (PSC) is proposed. The very first prototypes of laminated monolithic perovskite/silicon tandem solar cells with stable power output efficiencies of up to 20.0% are presented. Moreover, laminated single-junction PSCs are on par with standard sequential layer deposition processed devices in the same architecture. The numerous advantages of the lamination process are highlighted, in particular the opportunities to engineer the perovskite morphology, which leads to a reduction of non-radiative recombination losses and and an enhancement in open-circuit voltage (V _oc). Laminated PSCs exhibit improved stability by retaining their initial efficiency after 1-year aging and show good thermal stability under prolonged illumination at 80 °C. This lamination approach enables the research of new architectures for perovskite-based photovoltaics and paves a new route for processing monolithic tandem solar cells even with a scalable lamination process.

Nature Energy, Published online: 09 June 2022; doi:10.1038/s41560-022-01045-2

22.7%-Efficient perovskite solar cell and 25.5%-efficient perovskite/CIGS tandem solar cell are achieved by mixed solvents assisted GABr post-treatment strategy which effectively improves the quality of perovskite film, passivates defect and thus minimizes non-radiative recombination.

Abstract

The interface between the perovskite layer and the hole transport layer (HTL) plays a vital role in hole extraction and electron blocking in perovskite solar cells (PSCs), and it is particularly susceptible to harmful defects. Surface passivation is an effective strategy for addressing the above concerns. However, because of its strong polarity, isopropyl alcohol (IPA) is used as a solvent in all of the surface treatment materials reported thus far, and it frequently damages the surface of perovskite. In this paper, a method is proposed for dissolving the passivation materials, for example, guanidine bromide (GABr), in mixed solvents (1:1) of IPA and toluene (TL), which can efficiently passivate interface and grain boundary defects by minimizing the IPA solubility of the perovskite surface. As a result, all the performance parameters Voc, Jsc, and FF are improved, and the power conversion efficiency (PCE) increased from 20.1 to 22.7%. Moreover, combining the PSCs with GABr post-treatment in mixed solvents with copper indium gallium selenide (CIGS) solar cells, a 4-terminal (4T) perovskite/CIGS tandem device is realized and a PCE of 25.5% is achieved. The mixed solvent passivation strategy demonstrated here, hopefully, will open new avenues for improving PSCs’ efficiency and stability.

Publication date: 20 July 2022

Source: Joule, Volume 6, Issue 7

Author(s): Donglin Jia, Jingxuan Chen, Junming Qiu, Huili Ma, Mei Yu, Jianhua Liu, Xiaoliang Zhang

Two new hole-transporting materials (HTMs) with acceptor-rich (YJS001) and donor-rich (YJS003) are synthesized and characterized for hybrid perovskite photovoltaics applications. Under similar conditions, the efficiency of HTM YJS001 and YJS003-based devices is 17.43% and 20.81%, respectively. The superior performance of YJS003 over YJS001 is attributed to higher open-circuit voltage and fill factor from good hole transport, lower trap density, and lower electric resistance of cells.

Abstract

Interfaces play a decisive role in perovskite solar cells’ power conversion efficiency and their long-term durability. Small-molecule hole-transporting materials (HTMs) have grabbed enormous attention due to their structural flexibility, material properties, and stabilities, allowing for improved operational durability in perovskite photovoltaics. This study synthesizes and investigates a new class of benzimidazole-based small molecules, named YJS001 and YJS003, serving as the HTMs to enable high-efficiency mixed-cation mixed-halide perovskite solar cells. The benzimidazole-based materials are dopant-free HTMs composed of donor and acceptor building blocks that are designed to engineer the energy level alignment near the HTM/perovskite interface. Mixed-cation mixed-halide perovskites can be grown uniformly on both HTMs with large crystalline grains. It is discovered that the donor-rich YJS003-based solar cell exhibits a high open-circuit voltage of 1.09 V with a champion power conversion efficiency of over 20%. Power-dependent current–voltage characteristics of the solar cells are analyzed, from which the high performance of YJS003's excellent hole mobility and well-aligned energy level is attributed. This work introduces a new class of benzimidazole-based small molecules as HTMs, that paves the path for dopant free interface material development for commercialization of perovskite solar cells.

This work presents a study on commercially available, low-cost, and highly volatile naphthalene as a solid additive used in polymer solar cells (PSCs). Naphthalene is a promising processing solid additive that can be entirely volatilized without thermal annealing treatment and achieve higher efficiency with improved reproducibility and stability of PSCs.

Abstract

Highly volatile solid additives have attracted much attention recently because they enhance molecular packing order and possibly solve the problems of poor reproducibility and instability of polymer solar cells (PSCs) with solvent additives. The shortcoming is that existing solid additives require thermal annealing (TA) to remove them from the active layer, leading to an increase in the complexity of the device fabrication process and morphology rearrangement problems. This study introduces a commercially available, low-cost, and highly volatile material, naphthalene (NA), as a solid additive used in PSCs based on PM6: Y6. NA is well mixed with a non-fullerene acceptor and can restrict excessive aggregation of the donor and acceptor, producing efficiencies comparable to PSCs processed by 1-chloronaphthalene (CN) solvent additive. As a result, a maximum power conversion efficiency (PCE) of 16.52% for NA-processed PSC is achieved, higher than that of a PCE of 16.07% for CN-processed PSC with TA. NA-processed PSCs exhibit comparable efficiencies (PCE of 16.10%) without TA treatment and higher reproducibility/stability than CN-processed PSCs. This study demonstrates a low-cost and excellent volatile solid additive to improve the device performance and the potential for exploring new solid additives that can readily be made volatile without TA.

Thermal co-evaporation is used to access a unique perovskite composition, CsPbCl_2.5Br_0.5, which is scalable, thick, structurally uniform, and sufficiently robust to survive the deposition of indium tin oxide. Employing these active layers, the functional transparent photovoltaics are demonstrated to have record transparency, near-perfect color neutrality, decent power density, scalability, and high operational stability, offering a superior solution for low-power electronics with stringent aesthetic tolerance.

Abstract

Transparent photovoltaics (TPVs) can be integrated into the surfaces of buildings and vehicles to provide point-of-use power without impacting aesthetics. Unlike TPVs that target the photon-rich near-infrared portion of the solar spectrum, TPVs that harvest ultraviolet (UV) photons can have significantly higher transparency and color neutrality, offering a superior solution for low-power electronics with stringent aesthetic tolerance. In addition to being highly transparent and colorless, an ideal UV-absorbing TPV should also be operationally stable and scalable over large areas while still outputting sufficient power for its specified application. None of today's TPVs meet all these criteria simultaneously. Here, the first UV-absorbing TPV is demonstrated that satisfies all four criteria by using CsPbCl_2.5Br_0.5 as the absorber. By precisely tuning the halide ratio during thermal co-evaporation, high-quality large-area perovskite films can be accessed with an ideal absorption cutoff for aesthetic performance. The resulting TPVs exhibit a record average visible transmittance of 84.6% and a color rendering index of 96.5, while maintaining an output power density of 11 W m⁻² under one-sun illumination. Further, the large-area prototypes up to 25 cm² are demonstrated, that are operationally stable with extrapolated lifetimes of >20 yrs under outdoor conditions.

Methylammonium, bromide-free, and Sn-based perovskites are intriguing candidates to enable high-performance, stable, and low-toxic perovskite solar cells. It is expected that meticulous efforts will be required to improve perovskite film quality, device architecture, and fabrication techniques and push the efficiency closer to the theoretical Shockley–Queisser threshold value of over 30% in single-junction perovskite solar cells.

Abstract

Lead halide-based perovskite solar cells (PSCs) are intriguing candidates for photovoltaic technology because of their high efficiency, low cost, and simple process advantages. Owing to lead toxicity, PSCs based on partially/fully substituted Pb with tin have attracted tremendous attention, which would enable the ideal bandgap to approach the Shockley-Queisser (S-Q) limit. Especially, methylammonium (MA), bromide-free, tin-based perovskites are striking, because of the intrinsic poor stability of MA and blue shift caused by the incorporation of Br⁻. The first section of this review emphasizes the motivation for studying single-junction MA, Br-free, and Sn-based perovskites. The film quality improvement strategies of Sn-based perovskites, including additive, composition, dimensional, and interface engineering toward high-efficiency devices are comprehensively overviewed. Moreover, strategies to improve stability, where shelf, thermal and operational stabilities of the devices are summarized. Finally, this review concludes with a discussion of actual limitations and future prospects for Sn-based PSCs.

Nature Communications, Published online: 07 June 2022; doi:10.1038/s41467-022-30927-y