Chen Weijie

The nucleation and growth mechanisms of the phase transition between α and δ phase of formamidinium (FA)_{1− x} Cs _x PbI₃ are proposed. Based on these understandings, the lifetime of FA-dominated perovskite solar cells is successfully extended under humidity through either heat healing (leads to δ-to-α phase transition) or continuous 60 °C heating (kinetically stabilized α phase).

Abstract

Phase instability is one of the major obstacles to the wide application of formamidinium (FA)-dominated perovskite solar cells (PSCs). An in-depth investigation on relevant phase transitions is urgently needed to explore more effective phase-stabilization strategies. Herein, the reversible phase-transition process of FA_{1− x} Cs _x PbI₃ perovskite between photoactive phase (α phase) and non-photoactive phase (δ phase) under humidity, as well as the reversible healing of degraded devices, is monitored. Moreover, through in situ atomic force microscopy, the kinetic transition between α and δ phase is revealed to be the “nucleation–growth transition” process. Density functional theory calculation implies an enthalpy-driven α-to-δ degradation process during humidity aging and an entropy-driven δ-to-α healing process at high temperatures. The α phase of FA_{1− x} Cs _x PbI₃ can be stabilized at elevated temperature under high humidity due to the increased nucleation barrier, and the resulting non-encapsulated PSCs retain >90% of their initial efficiency after >1000 h at 60 °C and 60% relative humidity. This finding provides a deepened understanding on the phase-transition process of FA_{1− x} Cs _x PbI₃ from both thermodynamics and kinetics points of view, which also presents an effective means to stabilize the α phase of FA-dominated perovskites and devices for practical applications.

(BA)₄AgBiBr₈ 2D perovskite nanosheets are used to construct vertical heterostructures with 3D perovskite to serve as a barrier layer to suppress the ion diffusion and nonradiation recombination from 3D perovskite to metal electrode. The performance and stability of perovskite solar cells are simultaneously enhanced after the incorporation of the 2D nanosheets.

Abstract

Perovskite solar cells (PVSCs) have drawn great attention due to their high processability and superior photovoltaic properties. However, their further development is often hindered by severe nonradiative recombination at interfaces that decreases power conversion efficiency (PCE). To this end, a facile strategy to construct a 3D/2D vertical heterostructure to reduce the energy loss in PVSCs is developed. The heterostructure is contrived through the van der Waals integration of 2D perovskite ((BA)₄AgBiBr₈) nanosheets onto the surface of 3D-FAPbI₃-based perovskites. The large bandgap of (BA)₄AgBiBr₈ enables the formation of type-I heterojunction with 3D-FAPbI₃-based perovskites, which serves as a barrier to suppress the trap-assisted recombination at the interface. As a result, a satisfying PCE of 24.48% is achieved with an improved open-circuit voltage (V _OC) from 1.13 to 1.17 V. Moreover, the 2D perovskite nanosheets can effectively mitigate the iodide ion diffusion from perovskite to the metal electrode, hence enhancing the device stability. 3D/2D architectured devices retain ≈90% of their initial PCE under continuous illumination or heating after 1000 h, which are superior to 3D-based devices. This work provides an effective and controllable strategy to construct 3D/2D vertical heterostructure to simultaneously boost the efficiency and stability of PVSCs.

Nature Photonics, Published online: 08 August 2022; doi:10.1038/s41566-022-01046-3

Newly designed copolymers with multi-functionalities are synthesized and incorporated in perovskite solar cells to simultaneously improve device efficiency, stability, and mechanical resilience. The polymers form a hybrid cross-linked network composed of mixed physical and chemical bonds within the perovskite thin film, which provides controlled crystal growth and surface defect passivation, as well as effective energy dissipation and self-healing behaviors during and after mechanical deformation of devices.

Abstract

Mechanically resilient optoelectronic devices are relevant for a wide range of applications, including portable and wearable devices. Perovskite thin film-based devices are a suitable choice for designing such resilient systems as it demonstrates high performance while preserving moderate mechanical compliance. Yet its mechanical property can be improved further by integrating the energy dissipation system and self-healing ability into the thin film. Copolymers containing Lewis-base functional groups, elastomer chains, and cyclic linkages are synthesized and introduced into the perovskite precursor. The polymers impart multifunctional effect of controlled crystal growth, defect passivation, protection against moisture, mechanical energy dissipation, and self-recoverability. The polymer-added perovskite solar cells are shown to provide a power conversion efficiency of 23.25% (a steady-state efficiency of 22.61%), due to the strong coordinative covalent interaction between the polymer and the perovskite. An operational lifetime of solar cells under harsh conditions is also substantially extended by the polymer incorporation. Furthermore, the interchain hydrogen-bond strength controlled by the cyclic linkage, and hybrid cross-linked network formed within the thin film significantly improves the mechanical stability and self-recoverability of the thin film. As a result, the devices demonstrate robustness under 2000 cyclic flex tests at a bending radius of 1 mm.

Publication date: November 2022

Source: Journal of Energy Chemistry, Volume 74

Author(s): Zhongquan Wan, Hui Lu, Jinyu Yang, Yunpeng Zhang, Fangyan Lin, Jianxing Xia, Xiaojun Yao, Junsheng Luo, Chunyang Jia

Publication date: November 2022

Source: Journal of Energy Chemistry, Volume 74

Author(s): Qi Liu, Junming Qiu, Xianchang Yan, Yuemeng Fei, Yue Qiang, Qingyan Chang, Yi Wei, Xiaoliang Zhang, Wenming Tian, Shengye Jin, Ze Yu, Licheng Sun

Publication date: 21 September 2022

Source: Joule, Volume 6, Issue 9

Author(s): Hao Huang, Peng Cui, Yan Chen, Luyao Yan, Xiaopeng Yue, Shujie Qu, Xinxin Wang, Shuxian Du, Benyu Liu, Qiang Zhang, Zhineng Lan, Yingying Yang, Jun Ji, Xing Zhao, Yingfeng Li, Xin Wang, Xunlei Ding, Meicheng Li

Ga-doped Cz-Si material has been systematically analyzed with respect to its performance in high-efficiency solar cells with carrier selective junctions applying high-temperature TOPCon and low-temperature heterojunction processing. Ga-doped Cz-Si is due to its lower wafer cost and good performance an economically beneficial alternative to n-type wafer material.

Industrial mass production of solar cells is at a transition toward carrier-selective junction solar cells with passivating contacts such as TOPCon, POLO, or heterojunction technology (HJT). At the same time, many manufacturers consider switching from p-type Cz-Si to n-type Cz-Si wafers. This contribution indicates that Ga-doped p-type Cz-Si material is still a viable option for the new type of devices while giving an opportunity to benefit from lower wafer cost. The minority carrier diffusion lengths that are an order of magnitude larger than the thickness of the studied HJT and TOPCoRE devices are reported. Stability aspects for operation in the field are discussed. Best TOPCoRE solar cells on Ga-doped Cz-Si show a 0.2% higher efficiency than their co-processed n-type counterparts.