Chen Weijie

Two novel dopant-free hole transport materials (HTMs) named Y6-T and Y-T with a large conjugated electron-deficient core are developed for efficient perovskite solar cells. The champion power conversion efficiency (PCE) reaches 20.29% for Y-T-based device. The Y-T-based devices without encapsulation retain over 90% of the initial PCE in air with a relative humidity around 30% after storing for 60 days.

Abstract

Hole transport materials (HTMs) play a significant role in device efficiencies and long-term stabilities of perovskite solar cells (PSCs). In this work, two simple dopant-free HTMs are designed with a large conjugated electron-deficient core. On the one hand, a large coplanar backbone endows enhanced π–π stacking and reduced hole hopping distance. On the other hand, the incorporation of electron-deficient unit can easily tune the energy levels as well as increase hole mobilities. Combining these two advantages together, 12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro[1,2,5]thiadiazole[3,4-e]thieno[2″,3″:4,5]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5]thieno[3,2-b]indole is chosen as the large electron-deficient core to construct two novel dopant-free HTMs, Y6-T and Y-T. Both Y6-T and Y-T behave suitable highest occupied molecular orbital levels, good hole mobilities, as well as strong hydrophobicities. After careful device optimization with a passivation agent, Y-T delivers an impressive power conversion efficiency of 20.29%, which is higher than that of Y6-T (18.82%) and doped spiro-OMeTAD (19.24%). Moreover, PSCs based on Y6-T and Y-T show much better long-term stabilities than spiro-OMeTAD due to the intrinsic hydrophobicity. Therefore, this work provides a promising candidate as well as a useful design strategy for exploring dopant-free HTMs, which may pave the way for the commercialization of PSCs.

Thermal-aged precursor solution (TAPS) featuring the aggregated colloidal clusters with fewer nucleation sites is applied to fabricate high-quality quasi-2D perovskite films, through which a record-high V _OC of 1.24 V is achieved in (AA)₂MA₄Pb₅I₁₆-based quasi-2D perovskite solar cells, leading to a champion efficiency of 18.68%.

Abstract

Quasi-2D perovskites have received wide attention in photovoltaics owing to their excellent materials robustness and merits in the device stability. However, the highest power conversion efficiency (PCE) reported on quasi-2D perovskite solar cells (PSCs) still lags those of the 3D counterparts, mainly caused by the relatively high voltage loss. Here, a study is presented on the mitigation of voltage loss in quasi-2D PSCs via usage of thermal-aged precursor solutions (TAPSs). Based on the (AA)₂MA₄Pb₅I₁₆ (n = 5) quasi-2D perovskite absorber with a bandgap of ≈1.60 eV, a record-high open-circuit voltage of 1.24 V is obtained, resulting in boosting the PCE to 18.68%. The enhanced photovoltaic performance afforded by TAPS is attributed to the thermal-aged solution processing that triggers colloidal aggregations to reduce the nucleation sites inside the solution. As a result, formation of high-quality perovskite films featuring compact morphology, preferential crystal orientation, and lowered trap density is allowed. Of importance, with the improved film quality, the corrosion of Ag electrode induced by ion migrations is effectively restrained, which leads to a satisfactory storage stability with <2% degradation after 1200 h under nitrogen environment without encapsulation.

A polyoxometalate-based material CoW₁₂@MIL-101(Cr) is applied as an effective dopant to eliminate Pb⁰, passivate Pb²⁺ defects, and speeds up the volatilization of organic solvents during the crystallization of perovskite, resulting in a uniform and dense perovskite film. The doped device demonstrates an enhanced power conversion efficiency of 21.39% and excellent humid and thermal stability.

Abstract

The high-quality perovskite film with few defects plays an important role in the power conversion efficiency (PCE) and long-term stability of perovskite solar cells. Here, an efficient strategy is proposed to eliminate Pb⁰ and passivate Pb²⁺ simultaneously by employing a stable polyoxometalate-based material CoW₁₂@MIL-101(Cr) in the precursor solution of perovskite. The controllable oxidation ability of CoW₁₂ is optimized through the interaction with metal–organic frameworks, resulting in a doped perovskite film with regular morphology, large grain size, and low defects density. The solvent effects and formation of intermediate materials in the precursor solution are further investigated by an in situ thermogravimetry-Fourier transform infrared spectroscopy analysis. In addition, the champion doped-device showed enhanced PCE to 21.39% and excellent stability, maintaining 85% and 89% of the original PCE after heating at 85 °C in N₂ atmosphere and stored in ambient conditions (25 °C, 40% humidity) for 1000 h, respectively.

A new morphology control approach is developed to fabricate high-performance organic solar cells by utilizing the synergistic effect of 1-chloronaphthalene (CN) and dithieno[3,2-b:2′,3′-d]thiophene (DTT) additives. This approach exhibits general application in various active layer systems to achieve well-developed morphology, enabling outstanding power-conversion efficiency over 18.8% and fill factor exceeding 80% for the device based on PTQ10:m-BTP-PhC6:PC₇₁BM.

Abstract

Controlling the self-assembling of organic semiconductors to form well-developed nanoscale phase separation in the bulk-heterojunction active layer is critical yet challenging for building high-performance organic solar cells (OSCs). Particularly, the similar anisotropic conjugated structures between nonfullerene acceptors and p-type organic semiconductor donors raise more complexity on manipulating their aggregation toward appropriate phase separation. Herein, a new approach to tune the morphology of photoactive layer is developed by utilizing the synergistic effect of dithieno[3,2-b:2′,3′-d]thiophene (DTT) and 1-chloronaphthalene (CN). The volatilizable solid additive DTT with high crystallinity can restrict the over self-assembling of nonfullerene acceptors during the film casting process, and then allowing the refining of phase separation and molecular packing with the simultaneous volatilization of DTT under thermal annealing. Consequently, the PTQ10:m-BTP-PhC6:PC₇₁BM-based ternary OSCs processed by the dual additives of CN and DTT record a notable power-conversion efficiency of 18.89%, with a remarkable FF of 80.6%.

Publication date: December 2021

Source: Nano Energy, Volume 90, Part A

Author(s): Lipeng Wang, Zheng Yan, Jianhang Qiu, Jinbo Wu, Chao Zhen, Kaiping Tai, Xin Jiang, Shihe Yang

Efficient all-perovskite-based tandem photovoltaics (PV) are shown to be radiation hard, surpassing state-of-the-art industry-standard space PV. Combining high specific power with good resilience to the harsh radiation environment in space, they promise a next-generation of lightweight and cost-efficient solutions to power private space exploration, low-cost missions as well as future habitats on the Moon and Mars.

Abstract

Radiation-resistant but cost-efficient, flexible, and ultralight solar sheets with high specific power (W g⁻¹) are the “holy grail” of the new space revolution, powering private space exploration, low-cost missions, and future habitats on Moon and Mars. Herein, this study investigates an all-perovskite tandem photovoltaic (PV) technology that uses an ultrathin active layer (1.56 µm) but offers high power conversion efficiency, and discusses its potential for high-specific-power applications. This study demonstrates that all-perovskite tandems possess a high tolerance to the harsh radiation environment in space. The tests under 68 MeV proton irradiation show negligible degradation (<6%) at a dose of 10¹³ p⁺ cm⁻² where even commercially available radiation-hardened space PV degrade >22%. Using high spatial resolution photoluminescence (PL) microscopy, it is revealed that defect clusters in GaAs are responsible for the degradation of current space-PV. By contrast, negligible reduction in PL of the individual perovskite subcells even after the highest dose studied is observed. Studying the intensity-dependent PL of bare low-gap and high-gap perovskite absorbers, it is shown that the V _OC, fill factor, and efficiency potentials remain identically high after irradiation. Radiation damage of all-perovskite tandems thus has a fundamentally different origin to traditional space PV.

Electro-strictive strain in 3D polycrystalline perovskite is observed, which can lead to an accelerated ion migration under operational conditions. The 1D–3D perovskite, that is, 1D BnPbI₃ perovskite, spatially distributed in the 3D perovskite film and compensating the dangling bonds in the grain boundaries, can effectively inhibit electro-strictive responses and unbalanced charge carrier extraction, realizing ultralong operational stability.

Abstract

3D organic–inorganic hybrid halide perovskite solar cells (pero-SCs) inherently face severe instability issue due to ion migration under operational conditions. This ion migration inevitably results from the decomposition of ionic bonds under lattice strain and is accelerated by the existence of excess charge carriers. In this study, a 1D–3D mixed-dimensional perovskite material is explored by adding an organic salt with a bulk benzimidazole cation (Bn⁺). The Bn⁺ can induce 3D perovskite crystalline growth with the preferred orientation and form a 1D BnPbI₃ perovskite spatially distributed in the 3D perovskite film. For the first time, the electro-strictive response, which has a significant influence on the lattice strain under an electric field, is observed in polycrystalline perovskite. The 1D–3D perovskite can effectively suppress electro-strictive responses and unbalanced charge carrier extraction, providing an intrinsically stable lattice with enhanced ionic bonds and fewer excess charge carriers. As a result, the ion migration behavior of the p-i-n 1D–3D based pero-SC is dramatically suppressed under operational conditions, showing ultra-long-term stability that retains 95.3% of its initial power conversion efficiency (PCE) under operation for 3072 h, and simultaneously achieving an excellent PCE with a hysteresis-free photovoltaic behavior.

A molten-salt-assisted crystallization (MSAC) strategy is developed to improve the grain growth of all-inorganic perovskite films. MSAC enables more active mass transfer and interaction among precursor colloids. Devices based on the MSAC strategy show much increased efficiency to as high as 19.83% with open-circuit voltage as high as 1.2 V.

Abstract

Dynamic manipulation of crystallization is pivotal to the quality of polycrystalline films. A molten-salt-assisted crystallization (MSAC) strategy is presented to improve grain growth of the all-inorganic perovskite films. Compared with the traditional solvent annealing, MSAC enables more intensive mass transfer by means of convection and diffusion, which is beneficial to the interaction among the precursor colloids and to inducing in-plane growth of perovskite grains, resulting in the formation of high-quality perovskite films with suppressed pinhole and crack formation. Additionally, the introduction of molten salt alters the intermediate phases, and thus changes the crystallization pathways by reducing the energy barrier to produce films with desired optical and electrical properties. As a result, the MSAC strategy endows the devices with champion steady-state output efficiency of 19.83% and open-circuit voltage (V _oc) as high as 1.2 V, among the highest for this type of solar cell, thanks to its effectively reduced V _oc deficit.

One-step antisolvent-free hot-coating method is successfully used to fabricate Sn–Pb perovskite solar cells (PSCs) for the first time. Multiple cations are introduced to control the crystallization of the Sn–Pb film which produces PSCs with a champion power conversion efficiency over 15% and robust shelf stability. A novel ecofriendly approach for the fabrication of Sn–Pb PSCs is provided.

Pb-based perovskite solar cells (PSCs) have shown great potential in next-generation photovoltaics. However, the toxicity of Pb remains a big concern. Partial replacement of Pb with Sn is shown to reduce the toxicity of PSCs without considerably compromising the device performance. Currently, Sn–Pb single-junction PSCs have realized a champion power conversion efficiency (PCE) of 21.7%, whereas all perovskite tandem PSCs with a Pb–Sn device as the bottom cell have achieved a PCE of 25.5%. However, the fabrication process of Sn–Pb PSCs is still not ecofriendly due to the use of hazardous organic solvents and antisolvents. Herein, for the first time, a one-step antisolvent-free method is developed to fabricate a high-quality Sn–Pb perovskite film using methylammonium acetate (MAAc) ionic liquid as a green solvent. The crucial effects of multiple organic halides (MOHs) on the crystallization process and characteristics of the Sn–Pb film are comprehensively investigated. After optimizing the film fabrication parameters, PSCs with a champion PCE of 15.42% can be achieved. Moreover, the device exhibits robust stability that shows negligible PCE loss after being stored in N₂ for 720 h. A new avenue to promote the ecofriendly fabrication of efficient Sn–Pb PSCs is opened up.