Chen Weijie

Interface passivation of ultrathin Cu(In,Ga)Se₂ solar cells is important to achieve enhanced performance of solar cells. The potential of SiO₂ as a passivation layer and the implementation of nano‐patterning (production of sub‐micrometer contacts) on SiO₂ by optical lithography is investigated. Co‐relation between the dimensions of sub‐micrometer contacts and its implications on performance of the ultrathin passivated solar cells is thoroughly investigated.

Ultrathin Cu(In,Ga)Se₂ solar cells are a promising way to reduce costs and to increase the electrical performance of thin film solar cells. An optical lithography process that can produce sub‐micrometer contacts in a SiO₂ passivation layer at the CIGS rear contact is developed in this work. Furthermore, an optimization of the patterning dimensions reveals constrains over the features sizes. High passivation areas of the rear contact are needed to passivate the CIGS interface so that high performing solar cells can be obtained. However, these dimensions should not be achieved by using long distances between the contacts as they lead to poor electrical performance due to poor carrier extraction. This study expands the choice of passivation materials already known for ultrathin solar cells and its fabrication techniques.

Publication date: November 2018

Source: Nano Energy, Volume 53

Author(s): Sangyeob Lee, Jun Su Lee, Jiseong Jang, Ki-Ha Hong, Doh-Kwon Lee, Soomin Song, Kihwan Kim, Young-Joo Eo, Jae Ho Yun, Jihye Gwak, Choong-Heui Chung

Abstract

Graphical abstract

A pseudo‐3D CH₃CH₂CH₂NH₃PbI₃ perovskite film is deposited by a scalable dip‐coating technique with high surface coverage, and then conversed to a high‐quality 3D CH₃NH₃PbI₃ perovskite film via an organic‐cation displacement approach. With the MAPbI₃ film as the light absorber, planar perovskite solar cells are fabricated, affording stabilized power conversion efficiencies of 19.27% and 15.68% for 0.09 and 5.02 cm² devices, respectively.

Abstract

Methylammonium iodide (MAI) and lead iodide (PbI₂) have been extensively employed as precursors for solution‐processed MAPbI₃ perovskite solar cells (PSCs). However, the MAPbI₃ perovskite films directly deposited from the precursor solutions, usually suffer from poor surface coverage due to uncontrolled nucleation and crystal growth of the perovskite during the film formation, resulting in low photovoltaic conversion efficiency and poor reproducibility. Herein, propylammonium iodide and PbI₂ are employed as precursors for solution deposition of propylammonium lead iodide (PAPbI₃) perovskite film. It is found that the precursors have good film formability, enabling the deposition of a large‐area and homogeneous PAPbI₃ perovskite film by a scalable dip‐coating technique. The dip‐coated PAPbI₃ film is then subjected to an organic‐cation displacement reaction, resulting in MAPbI₃ film with high surface coverage and crystallinity. With the MAPbI₃ film as the light absorber, planar PSCs are fabricated, and stabilized power conversion efficiencies of 19.27% and 15.68% can be achieved for the devices with active areas of 0.09 and 5.02 cm², respectively. The technology reported here provides a robust and efficient approach to fabricate large‐area and high‐efficiency perovskite cells for practical application.

Publication date: 19 December 2018

Source: Joule, Volume 2, Issue 12

Author(s): Meng Zhang, Benjamin Wilkinson, Yuanxun Liao, Jianghui Zheng, Cho Fai Jonathan Lau, Jincheol Kim, Jueming Bing, Martin A. Green, Shujuan Huang, Anita Wing-Yi Ho-Baillie

Context & Scale

Summary

Graphical Abstract

Machine learning determines the optimal doping content of Mn²⁺ in CZTSSe films effectively and rapidly for the best solar cell efficiency. A CM_0.05Z_0.95TSSe solar cell with an efficiency of 8.93% is achieved in the experiment. The doped Mn²⁺ decreases the Cu_Zn defect and boosts the improvement of CZTSSe solar cells.

Isoelectronic cation substitution is a potential method to decrease the density of Cu‐Zn anti‐site defects in CZTSSe, thus improving the V _OC and performance of CZTSSe solar cells. The proper doping concentration is determined traditionally by the trial and error approach, costing much time, and materials. How to shorten the time to find the proper doping concentration is a big challenge for the development of solar cells. Here, by utilizing the machine learning model, the authors carry out an adaptive design for predicting the optimal doping ratio of Mn²⁺ ions in CZTSSe solar cells for improved solar cell efficiency. With the help of machine learning prediction, the authors rapidly and efficiently find the optimal doping ratio of Mn²⁺ in CZTSSe solar cells to be 0.05, achieving a highest solar cell efficiency of 8.9% in experiment. Further experimental characterizations of Mn‐doped CZTSSe show that the defect in CZTSSe after Mn doping is changed from an anti‐site Cu_Zn defect to V _Cu defect. Our findings suggest that machine learning is a very powerful and efficient approach to aid the development of solar cell materials for its application in the photovoltaic field.

Publication date: November 2018

Source: Nano Energy, Volume 53

Author(s): Xixia Liu, Bichen Li, Nengduo Zhang, Zhimeng Yu, Kuan Sun, Baoshan Tang, Diwen Shi, Hongyan Yao, Jianyong Ouyang, Hao Gong

Abstract

Graphical abstract

A novel cryogenic process has universal applicability to prepare mixed perovskite films. Excellent film quality and consequently promising device performance result from decoupling of nucleation and crystallization phases during the formation of perovskites. The cryogenic temperature suppresses premature reactions of the precursors and prevents premature coalescence of nuclei into large crystallites, enabling uniform film formation following the blow‐drying and annealing processes.

Abstract

A cryogenic process is introduced to control the crystallization of perovskite layers, eliminating the need for the use of environmentally harmful antisolvents. This process enables decoupling of the nucleation and the crystallization phases by inhibiting chemical reactions in as‐cast precursor films rapidly cooled down by immersion in liquid nitrogen. The cooling is followed by blow‐drying with nitrogen gas, which induces uniform precipitation of precursors due to the supersaturation of precursors in the residual solvents at very low temperature, while at the same time enhancing the evaporation of the residual solvents and preventing the ordered precursors/perovskite from redissolving into the residual solvents. Using the proposed techniques, the crystallization process can be initiated after the formation of a uniform precursor seed layer. The process is generally applicable to improve the performance of solar cells using perovskite films with different compositions, as demonstrated on three different types of mixed halide perovskites. A champion power conversion efficiency (PCE) of 21.4% with open‐circuit voltage (V _OC) = 1.14 V, short‐circuit current density ( J _SC) = 23.5 mA cm⁻², and fill factor (FF) = 0.80 is achieved using the proposed cryogenic process.