Ligang Yuan

Efficient indoor photovoltaics are achieved with wide bandgap metal halide perovskites. The optimal bandgap is first predicted with detailed balanced theory. The non-radiative recombination losses of the mixed-halide perovskites are reduced with both passivation in the bulk and interface with Pb(SCN)₂ and PEABr, respectively, which result in extremely high power conversion efficiency and open-circuit voltage under weak light illumination.

Abstract

Indoor photovoltaics have attracted increasing attention, since they can provide sustainable energy through the recycling of photon energy from household dim lighting. However, solar cells exhibiting high performance under sunlight may not perform well under indoor light conditions, mainly due to the mismatch of the irradiance spectrum. In particular, most of the indoor light sources emit visible photons with negligible near-infrared irradiance. According to the detailed balance theory, the optimal bandgap for indoor photovoltaics should be relatively larger, considering the trade-off between photocurrent and photovoltage losses. In this work, a systematic comparison of the theoretical limits of the conventional and indoor photovoltaics is presented. Then the non-radiative recombination losses are reduced by a synergetic treatment with Pb(SCN)₂ and PEABr, resulting relatively high open circuit voltage of 1.29 V and power conversion efficiency of 17.32% under 1 sun illumination. Furthermore, the devices are fully characterized under weak indoor light (1000 lux, 4000 K LED) achieving a high efficiency of 37.18%, which is promising for real applications.

Publication date: 15 October 2022

Source: Chemical Engineering Journal, Volume 446, Part 2

Author(s): Jiarong Wang, Ligang Yuan, Huiming Luo, Chenghao Duan, Biao Zhou, Qiaoyun Wen, Keyou Yan

Publication date: 18 May 2022

Source: Joule, Volume 6, Issue 5

Author(s): Minhuan Wang, Yepin Zhao, Xiaoqing Jiang, Yanfeng Yin, Ilhan Yavuz, Pengchen Zhu, Anni Zhang, Gill Sang Han, Hyun Suk Jung, Yifan Zhou, Wenxin Yang, Jiming Bian, Shengye Jin, Jin-Wook Lee, Yang Yang

Publication date: 15 September 2022

Source: Chemical Engineering Journal, Volume 444

Author(s): Zhen-Li Yan, Fang-Cheng Liang, Chia-Yu Yeh, Darwin Kurniawan, Jean-Sebastien Benas, Wei-Cheng Chen, Chia‐Jung Cho, Wei-Hung Chiang, Ru-Jong Jeng, Chi-Ching Kuo

Publication date: 15 September 2022

Source: Chemical Engineering Journal, Volume 444

Author(s): Wei-Min Gu, Ke-Jian Jiang, Fengting Li, Guang-Hui Yu, Yanting Xu, Xin-Heng Fan, Cai-Yan Gao, Lian-Ming Yang, Yanlin Song

Publication date: 15 August 2022

Source: Chemical Engineering Journal, Volume 442, Part 2

Author(s): Zhihong Yin, Xia Guo, Yang Wang, Lei Zhu, Yuhao Chen, Qunping Fan, Jianqiu Wang, Wenyan Su, Feng Liu, Maojie Zhang, Yongfang Li

An environmental-friendly PBAT polymer is adopted to implant the perovskite film with an anti-solvent method, which can passivate the uncoordinated Pb²⁺ and neutral iodine defects of perovskite material and markedly improve device efficiency and operational stability. More importantly, the polymer network can prevent nearly 98% of Pb²⁺ from leaking by directly immersing the polymer-coated perovskite film in water.

Abstract

Although perovskite solar cells (PSCs) are on the road to industrialization, the operational stability under high efficiency still needs to be improved, and the water solubility of lead ions (Pb²⁺) will cause environmental pollution problems. Herein, it is successfully implanted an environment-friendly (biodegradability) poly(butylene adipate-coterephthalate) polymer (PBAT) into the perovskite film, which can passivate the uncoordinated Pb²⁺ and neutral iodine defects of the perovskite material because of the adequate carbonyl groups and benzene rings in PBAT polymer, thereby regulating the crystallization of perovskite film with lower trap density, inhibiting the nonradiative recombination and improving charge carrier transport. As a result, the polymer-incorporated inverted PSCs achieve optimal conversion efficiencies of 22.07% (0.1 cm²) and 20.31% (1 cm²). Meanwhile, the incorporated device, after being encapsulated, exhibits a prominent improvement in operational stability of high-efficiency device under maximum power point tracking and continuous one sunlight illumination, maintaining the initial efficiency of 80% for 3249 h. More importantly, the polymer network can protect Pb²⁺ from being dissolved by water and prevent nearly 98% of Pb²⁺ from leaking by directly immersing the polymer-coated perovskite film in water. Environmental-friendly molecules provide new hope for solving lead poisoning and improving device operational stability under high efficiency.

Nature, Published online: 13 April 2022; doi:10.1038/s41586-022-04455-0

A two-step orthogonal solvent method that enables straightforward fabrication of multilayer perovskite films is applied to construct the perovskite/carbon heterojunction for carbon-based perovskite solar cells (PSCs). Such a bulk heterojunction (BHJ) improves the interface contact and facilitates the hole transport between perovskite and the carbon electrode, significantly boosting the power conversion efficiency (PCE) to 16.4% with certification.

An efficient perovskite junction is critical for the functioning of perovskite solar cells (PSCs). However, carbon-based perovskite solar cells (C-PSCs) have been plagued by the paucity of ways to construct an efficient junction between perovskite and carbon, staggering around an efficiency much lower than other state-of-the-art PSCs. Herein, a perovskite/carbon bulk heterojunction (BHJ) for C-PSCs is innovated and systematically studied. First, a two-step orthogonal solvent method is developed to deposit a series of high-quality perovskite films directly on the preformed perovskite film, allowing to manipulate compositions, band alignment, and charge transfer of the perovskite junction in a low-cost and straightforward fashion. Second, by adopting this method to a porous carbon electrode as originally motivated, fabrication of perovskite/carbon BHJ with perovskite crystals by seamlessly filling in the porous carbon film is successfully done, thus providing a high contact area of perovskite/carbon heterojunction. Such a BHJ accelerates hole collection of the carbon electrode from the perovskite layer, thus significantly boosting the performance of C-PSCs with MAPbI₃ as the active layer from 12% to over 16% with certification. The device is shown to be stable with no obvious degradation after 1700 h of continuous light soaking near the maximum power point.

Publication date: 20 April 2022

Source: Joule, Volume 6, Issue 4

Author(s): Jiwei Liang, Xuzhi Hu, Chen Wang, Chao Liang, Cong Chen, Meng Xiao, Jiashuai Li, Chen Tao, Guichuan Xing, Rui Yu, Weijun Ke, Guojia Fang

Publication date: 15 August 2022

Source: Chemical Engineering Journal, Volume 442, Part 2

Author(s): Hongru Ma, Minhuan Wang, Yudi Wang, Qingshun Dong, Jing Liu, Yanfeng Yin, Jie Zhang, Mingzhu Pei, Linghui Zhang, Wanxian Cai, Lei Shi, Wenming Tian, Shengye Jin, Jiming Bian, Yantao Shi

A versatile manufacturing technology, solvent-annealing assisted thermal evaporation (SATE), is introduced to effectively modulate organic film morphology as well as optoelectronic properties. The SATE method produces undoped spiro-OMeTAD layers with high density, good film homogeneity, enhanced conductivity, and remarkable film stability, which leads to a 36% enhancement of power conversion efficiency to 20.02% and remarkable stability. This work demonstrates that SATE can be generally applicable to controllable fabrication of organic thin film and reliable devices.

Abstract

Thermal evaporation (TE) as a scalable and low-cost technique for fabrication of organic hole transport materials (HTMs) typically produces low photovoltaic performance and poor device reproducibility in the application of perovskite solar cells (PSCs), and there is a clear need to understand the weaknesses of TE. Here, a versatile manufacturing technology, solvent-annealing assisted thermal evaporation (SATE), enabling effective modulation of organic film morphology as well as optoelectronic properties, is introduced. The SATE method produces undoped spiro-OMeTAD layers with high density, good film homogeneity, enhanced conductivity, and remarkable film stability, all of which are superior to that made by conventional TE. In addition, SATE films eliminate the dopant induced degradation mechanism and simultaneously improve the electrical conductivity of undoped HTMs. Significantly, the resulting devices yield a 36% enhancement of power conversion efficiency (PCE) from 14.68% (TE) to 20.02% (SATE), which is the highest reported PCE for evaporated HTMs in n–i–p PSCs. Moreover, unencapsulated PSC devices with SATE demonstrate an impressive environmental and thermal stability by maintaining 85% of initial performance after 2500 h in air with 30% humidity. The high efficiency with simultaneously improved stability demonstrates SATE can be generally applicable to controllable fabrication of organic thin film and reliable devices.

Homologous PbI₂ in situ passivation strategy is demonstrated to passivate defect at grain boundaries of black-phase FAPbI₃ film via methylamine chloride-assisted one-step deposition. The excess PbI₂ based self-passivation on the FAPbI₃ device not only enhances the power conversion efficiency from 14.87% to 22.13% but also leads to excellent durability in air, which is the highest PCE for FAPbI₃-based inverted PSCs reported to date.

Abstract

Formamidinium lead iodide (FAPbI₃) has endowed power conversion efficiencies (PCEs) up to 25.5% in regular-structured perovskite solar cells (PSCs) because of its optimal bandgap and enhanced thermal stability. However, the performance of FAPbI₃-based inverted-structured PSCs is unsatisfactory. Herein, four kinds of commonly used hole transport materials (HTMs) are selected, including PEDOT:PSS, PTAA, NiOx, and MeO-2PACz, to study their impact on the methylamine chloride (MACl)-assisted one-step deposition of FAPbI₃ films. It is found that MeO-2PACz is the optimal substrate for stabilizing black-phase FAPbI₃ and the corresponding inverted-structured PSCs show the best photovoltaic performance. Nonetheless, the PCE is restricted by low open-circuit voltage (V _OC) due to non-radiative recombination caused by MACl residues. Therefore, homologous PbI₂ in situ passivation is implemented to passivate defects at grain boundaries. The addition of excess PbI₂ in precursor solution remarkably decreases charge trap densities and elongates carrier lifetimes. As a result, the optimized device achieves an impressive PCE of 22.13%, which is the highest efficiency of FAPbI₃ based on inverted-structured PSCs. Moreover, the best device exhibits free hysteresis and excellent long-term stability, maintaining 92% of the initial PCEs after 800 h aging under ambient conditions.

A bottom-up infiltration method using HCOONH₄ as pre-buried additive in SnO₂ electron transport layer (ETL) enables a cross-layer defect manipulation throughout the SnO₂ ETL, perovskite layer, and their interface, along with a significantly reduced residual stress within perovskite film. As a result of the cross-layer treatment, a record power conversion efficiency of 22.37% (21.90% certified) is achieved on the optimized flexible perovskite solar cells.

Abstract

Halide perovskites have shown superior potentials in flexible photovoltaics due to their soft and high power-to-weight nature. However, interfacial residual stress and lattice mismatch due to the large deformation of flexible substrates have greatly limited the performance of flexible perovskite solar cells (F-PSCs). Here, ammonium formate (HCOONH₄) is used as a pre-buried additive in electron transport layer (ETL) to realize a bottom-up infiltration process for an in situ, integral modification of ETL, perovskite layer, and their interface. The HCOONH₄ treatment leads to an enhanced electron extraction in ETL, relaxed residual strain and micro-strain in perovskite film, along with reduced defect densities within these layers. As a result, a top power conversion efficiency of 22.37% and a certified 21.9% on F-PSCs are achieved, representing the highest performance reported so far. This work links the critical connection between multilayer mechanics/defect profiles of ETL-perovskite structure and device performance, thus providing meaningful scientific direction to further narrowing the efficiency gap between F-PSCs and rigid-substrate counterparts.

Publication date: 15 June 2022

Source: Nano Energy, Volume 97

Author(s): Yu-Jin Kang, Seok-In Na

It is demonstrated that solution engineered perovskite nanocrystals enable efficient electroluminescence and photovoltaics performance within a single device through tailoring the dispersity and interface. It delivers the maximum brightness of 490 W sr⁻¹ m⁻² at 2.7 V and 23.2% electroluminescence external quantum efficiency, as well as 15.23% photovoltaic efficiency.

Abstract

Integrating highly efficient photovoltaic (PV) function into light-emitting diodes (LEDs) for multifunctional display is of great significance for compact low-power electronics, but it remains challenging. Herein, it is demonstrated that solution engineered perovskite nanocrystals (PNCs, ≈100 nm) enable efficient electroluminescence (EL) and PV performance within a single device through tailoring the dispersity and interface. It delivers the maximum brightness of 490 W sr⁻¹ m⁻² at 2.7 V and 23.2% EL external quantum efficiency, a record value for near-infrared perovskite LED, as well as 15.23% PV efficiency, among the highest value for nanocrystal perovskite solar cells. The PV–EL performance is well in line with the reciprocity relation. These all-solution-processed PV-LED devices open up viable routes to a variety of advanced applications, from touchless interactive screens to energy harvesting displays and data communication.

Long-chain n-heptylamine is introduced via antisolvent engineering into a formamidine (FA)-based perovskite film, which promotes the formation of α-FAPbI₃ at room temperature in humid air via intermolecular exchange behavior. The champion device delivers a power conversion efficiency of 23.7% (certificated 22.76%) with negligible hysteresis and superior stability.

Abstract

Preparation of high-performance perovskite solar cells without strict environmental control is an inevitable trend of commercialization. Humidity is considered the main factor hindering perovskite performance. Formamidine (FA)-based perovskites suffer from the instability of photoactive black α-FAPbI_3, especially in humid air, and numerous defects in the surface and bulk of perovskite films limit their performance. In this work, long-chain n-heptylamine (nHA) is introduced via antisolvent engineering into an FA-based perovskite film. nHA removes the negative intermediate adduct and promotes the formation of α-FAPbI₃ at room temperature in humid air via intermolecular exchange behavior. Moreover, the existence of nHA in the final perovskite film also reduces the defects and suppresses ion migration. The champion device delivers a power conversion efficiency (PCE) of 23.7% (certificated 22.76%) with negligible hysteresis, and the fabricated devices exhibit superior reproductivity. The device stability is also enhanced, maintaining 95% of its initial PCE after 1500 h in ambient air. Moreover, the PCE has no attenuation at the maximum power point under continuous 1-sun light soaking for 500 h. The universality of this method is also demonstrated by other perovskite compositions, including methylamine lead iodine (MAPbI₃) and FA _x MA_{1− x} PbI₃ in humid air.

Bulk and surface treatment of formamidium lead iodide perovskite with chlorine-based compounds promote an enhancement of the solar cell photovoltaic conversion efficiency (PCE), by simultaneously improving the active layer crystallinity and morphology, thus increasing the short-circuit current density, and suppressing nonradiative losses, boosting the device open-circuit voltage.

Defect-mediated recombination losses limit the open-circuit voltage (V _OC) of perovskite solar cells (PSCs), negatively affecting the device's performance. Bulk and dimensional engineering have both been reported as promising strategies to passivate shallow defects, thus improving the photovoltaic conversion efficiency (PCE). Here, a combined bulk and surface treatment employing chlorine-based compounds is employed. Methylammonium chloride (MACl) is used as a bulk additive, while 4-methylphenethylammonium chloride (MePEACl) is deposited onto the perovskite surface to produce a low-dimensional perovskite (LDP) and reduce nonradiative recombination. Through structural and morphological investigations, it can be confirmed that bulk and surface doping have a beneficial effect on the film morphology and its overall quality, while electroluminescence (EL) and photoluminescence (PL) analyses demonstrate an increased and more homogeneous emission. Applying this double passivation strategy in PSC fabrication, a boost is observed in both the short-circuit current density and the V _OC of the devices, achieving a champion 21.4% PCE while improving device stability.

Publication date: 15 August 2022

Source: Chemical Engineering Journal, Volume 442, Part 1

Author(s): Shengwen Li, Junmin Xia, Chao Liang, Zhaorui Wen, Zhen Mu, Kaiyang Wang, Hao Gu, Shiliang Mei, Hui Pan, Jiangzhao Chen, Guichuan Xing, Shi Chen