Chen Weijie

Publication date: November 2020

Source: Nano Energy, Volume 77

Author(s): Naveen Harindu Hemasiri, Samrana Kazim, Shahzada Ahmad

Publication date: November 2020

Source: Nano Energy, Volume 77

Author(s): Sungwoo Jung, Jiyeon Oh, U. Jeong Yang, Sang Myeon Lee, Jungho Lee, Mingyu Jeong, Yongjoon Cho, Seoyoung Kim, Jeong Min Baik, Changduk Yang

Publication date: 10 September 2020

Source: Chem, Volume 6, Issue 9

Author(s): Jun Yuan, Huotian Zhang, Rui Zhang, Yuming Wang, Jianhui Hou, Mario Leclerc, Xiaowei Zhan, Fei Huang, Feng Gao, Yingping Zou, Yongfang Li

A new PBTI2(30HD)‐FT terpolymer acceptor enables all‐polymer solar cells (all‐PSCs) with an ultrabroad donor:acceptor (D:A) ratio tolerance from 1:30 to 10:1 and better stability than other types of organic solar cells. PBTI2(30HD)‐FT can lead to well‐maintained interpenetrating network even at very low loading in blend films, yielding decent photovoltaic performance.

Achieving a broad donor:acceptor (D:A) composition tolerance in efficient organic solar cells (OSCs) is important for printing large‐area solar cell modules. Herein, all‐polymer solar cells (all‐PSCs) based on new terpolymer acceptors and a well‐known polymer donor PTB7‐Th are fabricated to explore the effect of D:A ratio on morphology and photovoltaic performances. The all‐PSCs show a promising power conversion efficiency (PCE) of 7.23% with an optimum D:A ratio of 1:2 and retain over 40% of its optimal PCE with ultrabroad D:A composition tolerance from 1:30 to 10:1. In addition, the all‐PSCs can maintain 90% of its original PCE after 400 h of storage despite such broad range of D:A ratio, which is much better than those of other types of OSCs and even better than the benchmark all‐polymer system with N2200 as the acceptor under the same condition. The results show the superiority of the all‐PSCs in terms of D:A ratio tolerance and performance stability, which should be conducive to practical applications of all‐PSCs.

As a promising emerging photovoltaic material in recent years, perovskite nanocrystal solar cells have attracted increasing interest but face many challenges. This paper presents a comprehensive review of their unique photoelectronic properties, characterizations, recent progress, and the current challenges of perovskite nanocrystal solar cells and, finally, points out the focus of future research.

Abstract

Perovskite nanocrystal (PNC) solar cells have attracted increasing interest in recent years because of their excellent optoelectronic properties and unique advantages, which distinguish them from conventional nanocrystals and their bulk counterparts. This emerging type of photovoltaic is promising but faces many challenges regarding commercialization. Therefore, a comprehensive review is presented on the recent progress and current challenges in PNC solar cells. It begins by reviewing the optoelectronic, unique properties of PNCs for photovoltaic devices. Then, the limiting factors on performance are detailed and analyzed with respect to the Shockley–Queisser limit, followed by a summary of effective strategies for efficiency improvement alongside other promising ideas. Finally, the present challenges are discussed toward high‐efficiency, stable, easy‐to‐process, and low‐cost, commercial, PNC photovoltaics. This review aims to attract further attention to the design and development of PNC solar cells, which will accelerate their progress.

A series of phenylhydroxylammonium halide salts is adopted to passivate the surface of the mixed perovskite film, resulting in enormously enhanced photoluminescence (PL) intensity and prolonged carrier lifetime. As a result, the best perovskite solar cell treated with phenylbutylammonium bromide realizes a power conversion efficiency (PCE) of 22.67% with a V _oc of 1.216 V, corresponding to a small V _oc deficit of ≈344 mV.

Abstract

Suppressing non‐radiative recombination via passivating surface defects of perovskite films has demonstrated an excellent strategy for high‐performance perovskite solar cells (PSCs). However, it is still hard to realize both high open‐circuit voltage (V _oc) of >1.2 V and high power conversion efficiency (PCE) of >22%, because the optimized bandgap of perovskite films is less than 1.60 eV for efficient light harvesting and V _oc deficit is generally unavoidable due to carriers recombination. Here, the surface of the perovskite film is treated with a series of phenylhydroxylammonium halide salts and it is found that all of them can remarkably prolong the carrier lifetime owing to their excellent capability of surface defects passivation. The best PSC with phenylbutylammonium bromide treatment realizes a PCE of 22.67% with a V _oc of 1.216 V, corresponding to a small V _oc deficit of ≈344 mV.

The charge‐extracting properties of PC₆₀BM, the electron transporting layer (ETL) widely used in perovskite solar cells, are greatly enhanced by complementing with Al:ZnO and triphenyl‐phosphine oxide films. Using these triple‐ETL results in a major improvement in device performance in terms of both efficiency and stability, due to better energy alignment, reduced trap‐assisted recombination, and higher built‐in voltage.

Abstract

Power conversion efficiencies of perovskite solar cells (PSCs) have rapidly increased from 3.8% to a certified 25.2% within only a decade. Eliminating possible recombination losses at the interfaces is essential to further improve both efficiency and stability of this class of emerging photovoltaic technology. Herein, a simple approach for improving the electron extraction of the PC₆₀BM electron transport layer (ETL) is presented by sequentially depositing Al:ZnO (AZO) and triphenyl‐phosphine oxide (TPPO) on top of it, in a p–i–n device configuration. The efficiency of the resulting CH₃NH₃PbI₃‐based solar cell is shown to improve from 14.6%, measured for the control PC₆₀BM‐only cell, to 17.9% for double‐ETL (PC₆₀BM/AZO) and 19.2% for triple‐ETL (PC₆₀BM/AZO/TPPO)‐based devices, respectively. Optimized triple‐ETL‐based cells exhibit high fill factor of 82%. The combination of electrical and quantum mechanical calculations shows that efficiency improvement is attributed to reduced trap‐assisted recombination at the interface and better energy level alignment due to chemical interactions between PC₆₀BM, AZO, and TPPO. Moreover, it is shown that the use of multilayer ETL results in better device stability (T ₈₀ ≈ 800 h) under constant illumination. This work opens new possibilities for inexpensive highly efficient and stable multilayered contacts for PSCs by combining organic small molecules and metal oxides.

High‐efficiency solution‐processed hybrid tandem photovoltaic devices, employing inorganic perovskite and organic bulk‐heterojunction as the photoactive layers, are demonstrated. A PCE of 18.04% in the hybrid tandem device is achieved, which is significantly higher than the comparable single‐junction devices, owing to a near‐optimal absorption spectral match.

Abstract

Although the power conversion efficiency (PCE) of inorganic perovskite‐based solar cells (PSCs) is considerably less than that of organic‐inorganic hybrid PSCs due to their wider bandgap, inorganic perovskites are great candidates for the front cell in tandem devices. Herein, the low‐temperature solution‐processed two‐terminal hybrid tandem solar cell devices based on spectrally matched inorganic perovskite and organic bulk heterojunction (BHJ) are demonstrated. By matching optical properties of front and back cells using CsPbI₂Br and PTB7‐Th:IEICO‐4F BHJ as the active materials, a remarkably enhanced stabilized PCE (18.04%) in the hybrid tandem device as compared to that of the single‐junction device (9.20% for CsPbI₂Br and 10.45% for PTB7‐Th:IEICO‐4F) is achieved. Notably, the PCE of the hybrid tandem device is thus far the highest PCE among the reported tandem devices based on perovskite and organic material. Moreover, the long‐term stability of inorganic perovskite devices under humid conditions is improved in the hybrid tandem device due to the hydrophobicity of the PTB7‐Th:IEICO‐4F back cell. In addition, the potential promise of this type of hybrid tandem device is calculated, where a PCE of as much as ≈28% is possible by improving the external quantum efficiency and reducing energy loss in the sub‐cells.

A novel BDT‐based random polymeric hole‐transporting layer (asy‐ranPBTBDT) is developed with irregularity from asymmetric substitution and random copolymerization. The resulting low crystallinity from the irregularity leads to superior solubility capacity and suppressed charge recombination and morphological changes. Therefore, the colloidal quantum dot solar cells using asy‐ranPBTBDT‐based device show highly efficient power conversion efficiency of 13.2% with superior operational stability.

Abstract

Next‐generation solution‐processed solar cells will hopefully be processed using green solvents, and will unite high performance with operating stability. Colloidal quantum dot/polymer hybrid solar cells are of interest for their harvest of the visible as well as the near infrared; however, today's best polymer hole‐transporting layers (HTLs) rely on processing using hazardous solvents such as chlorobenzene. This stems from the strong polymer–polymer attraction in polymeric p‐type materials, which accounts for their limited solubility. Here, a new random polymeric HTL (asy‐ranPBTBDT) is reported that is soluble in green solvents such as 2‐methylanisole without compromising ultimate device power conversion efficiency. The new polymer structure induces a strong π–π stacking face‐on orientation and less lateral grain growth compared to control asy‐PBTBDT, leading to reduced charge recombination and improved device stability. The resulting device exhibits a power conversion efficiency (PCE) of 13.2% and retains 89% of its initial efficiency after 120 h of continuous device operation at the maximum power point, compared to a PCE of 11.4% and 71% degradation for control devices.

To generate cost‐efficient and high‐performanced polymers, a simple chemical steric effect (SE) is introduced to benzothiophene (BDT)‐based side chains. The polymeric crystallinity and miscibility are rebalanced and a power conversion efficiency (PCE) of 14.53% is achieved. Thus, the SE applied in crystalline polymer pave an easier and cheaper route to realize the coordination of low‐cost fabrication and high‐performance.

Abstract

Low synthetic cost and high performance are becoming a new challenge in designing polymer donors for large‐scaled polymer solar cells (PSCs) fabrication; however, complicated synthetic routes and high material costs hamper the widespread commercial application of OPVs. Here, a simple and low‐cost chemical steric effect (SE) is introduced to BDT‐based side chains. Through adjusting alkyl side chains, the polymeric crystallinity and miscibility are rebalanced and subsequently the photovoltaic device based on the meta‐positioned alkyl polymer outperforms its para‐positioned counterpart. The champion device based on the polymer with the meta‐positioned side chains affords a PCE of 14.53% without sacrificing its high fill factor of 0.77, which could be attributed to a more balanced charge‐carrier transport ability and optimized morphology. This is the highest PCE value reported in BTZ based polymer donors to date. Thus, it shows that the SE applied in high crystalline polymer could pave an easier and cheaper chemical route to realize the coordination of low‐cost fabrication and high‐performance.

This study reports the deposition of a TiO₂ electron transporting layer for perovskite solar cells by spray coating using a stable TiO₂ colloidal aqueous solution, which is synthesized via the self‐condensation of a titanium peroxide complex under hydrothermal conditions. Although the whole fabrication process for the cells is performed at 100 °C, 22.7% efficiency is achieved.

Abstract

TiO₂ is one of the most efficient and widely used materials for electron‐transporting layer (ETLs) in perovskite solar cells (PSCs). The formation of efficient TiO₂ layers is generally carried out at high temperature by baking at a temperature >400 °C or by vacuum deposition (e.g., atomic layer deposition and E‐beam). In this study, the preparation of a TiO₂ ETL for PSCs is reported with excellent properties at low temperatures based on the synthesis of a stable TiO₂ colloidal aqueous solution and spray coating. The prepared TiO₂ colloids are able to produce a dense and uniform ETL even if it is simply dried at 100 °C after spray coating. It is believed that this is owing to the peroxo functional group remaining on the surface of the TiO₂ colloids. The TiO₂ ETLs, combined with the TiO₂ underlayer formed by chemical bath deposition, and the sprayed TiO₂ colloids allowed the fabrication of PSCs with performance similar to those of PSCs produced by annealing at 450 °C with a TiO₂ paste. The PSCs fabricated entirely at 100 °C demonstrated power conversion efficiency of 22.7% in small cells, and 19.0% in mini‐modules.

Nature, Published online: 02 September 2020; doi:10.1038/s41586-020-2621-1

Carbon nanotube electrode–laminated perovskite and n‐type tunnel oxide–passivated contact (TOPCon) silicon solar cells exhibit 24.42% efficiency when stacked in tandem. Both semitransparency and power conversion efficiency are important for top subcells of tandem solar cells. The carbon nanotube‐based perovskite solar cells demonstrate record high efficiency among the reported four‐terminal tandem solar cells while exhibiting good semitransparency.

Carbon nanotube electrode–laminated perovskite solar cells in combination with n‐type tunnel oxide–passivated contact silicon solar cells demonstrate a high power conversion efficiency (PCE) of 24.42% when stacked in tandem. This is compared with conventional indium tin oxide/MoO _x ‐deposited perovskite solar cells which give an efficiency of 22.35% when stacked in the same four‐terminal tandem system. Despite higher transmittance of the carbon nanotube electrode than that of the indium tin oxide/MoO _x in the infrared range, the carbon nanotube electrode‐laminated devices show lower transmittance in the same region due to the total internal reflection and scattering as evidenced by optical simulation. Yet, the exceptionally high PCE of the carbon nanotube electrode‐laminated semitransparent devices far exceeding than that of the indium tin oxide/MoO _x ‐deposited semitransparent top cell outweighs the effect of the optical transparency. Four types of silicon solar cells are compared as the bottom subcells, and the n‐type tunnel oxide‐passivated contact silicon solar cells are the best choice mainly due to their high absorption in the long‐wavelength region. The obtained 24.42% efficiency is one of the high PCEs among the reported four‐terminal perovskite–silicon solar cells, and this article is the first demonstration of the carbon nanotube electrode application in tandem solar cells.

The combination of two well‐defined conjugated small‐molecule (SM) donors FG3 and FG4 and Y6 as well‐known nonfullerene SM acceptors provides the fabrication of efficient ternary OSCs. This contribution shows an excellent power conversion efficiency (PCE) of 14.31% with a high fill factor (FF) and J _sc, in contrast with the binary counter parts.

An efficient organic solar cell (OSC) based on a ternary active layer consisting of two conjugated small‐molecule (SM) donors (FG3 and FG4) and a well‐known nonfullerene SM acceptor (Y6) is fabricated using a nonhalogenated solvent. An overall power conversion efficiency (PCE) of 14.31% is achieved, higher than that for the binary counterparts, i.e., 10.75% and 11.07% for FG3:Y6 and FG4:Y6, respectively. The short‐circuit current density (J _SC) of the ternary active layer organ is related to the broader absorption spectra when compared with the binary active layers. The open‐circuit voltage (V _OC) of the ternary active layer‐based OSCs falls between those of the OSCs based on FG3:Y6 and FG4:Y6, a situation that is consistent with the lowest unoccupied molecular orbital (LUMO) level of both SM donors (FG3 and FG4), and forms the alloy between the two donors. The overlap of the absorption spectra of FG4 with the photoluminescence of FG3 confirms the energy transfer from FG3 to FG4 and this leads to improvement in J _SC. The balanced charge transport, reduced charge recombination, and the fast charge extraction in the ternary active layer leads to the higher fill factor (FF) value. A combination of all of these effects affords a high PCE value.

Recent advances in near‐infrared‐transparent perovskite and perovskite‐based tandem solar cells are reviewed. The factors limiting their performance, and strategies for further improvement are discussed. The challenges limiting their commercialization and outlook for technology advancements are presented.

Abstract

Metal halide perovskite solar cells (PSCs) have gained tremendous attention due to their high power conversion efficiencies (PCEs) and potential for low‐cost manufacturing. Their wide and tunable bandgap makes perovskites an ideal candidate for tandem solar cells (TSCs) with well‐established narrow bandgap photovoltaic technologies, such as crystalline silicon and Cu(In,Ga)Se₂, to boost the PCEs beyond the Shockley–Queisser limit at affordable additional cost. Although perovskite‐based TSCs have shown rapid progress over the past few years, they are far from reaching their practical efficiency limit. In addition, technology commercialization needs to overcome several challenges such as processing upscalability and long‐term operational stability of solar modules. In this review, a comprehensive overview of the recent progress of perovskite‐based TSCs is provided and the key challenges in the field are discussed. First, the structural and optoelectronic properties of metal halide perovskite materials and preparation methods of metal halide perovskite layers are introduced. Next, the important constituents of near‐infrared (NIR) transparent PSCs for achieving high efficiency along with high NIR transmittance are highlighted. Then the developments in perovskite‐based TSCs are reviewed, the limiting factors are outlined, and strategies to boost the efficiencies well beyond 30% are provided. Finally, the review is concluded by highlighting the bottlenecks for commercialization and providing an outlook for technology advancement.