Recovery Mechanisms in Aged Kesterite Solar Cells

Abstract

For successful long-term deployment and operation of kesterites Cu 2 ZnSn(S x Se 1– x ) 4 (CZTSSe) as light-absorber materials for photovoltaics, device stability and recovery in kesterite solar cells are investigated. A low-temperature heat treatment is applied to overcome the poor charge extraction that developed in the natural aging process. It is suggested that defect states at aged CZTSSe/CdS heterojunctions were reduced, while apparent doping density in the CZTSSe absorber increased due to Cd/Zn interdiffusion at the heterojunction during the annealing process. In situ annealing experiments in a transmission electron microscope were used to investigate the elemental diffusion at the CZTSSe/CdS heterojunction. This study reveals the critical role of heat treatment to enhance the absorber/Mo back contact, improve the quality of the absorber/buffer heterojunction, and recover the device performance in aged kesterite thin-film solar cells.

Performance Degradation in Solution-Processed Cu2ZnSn(S,Se)4 Solar Cells Based on Different Oxidation States of Copper Salts

“…The increase in R s observed in the devices can plausibly be attributed to the presence of a Schottky potential energy barrier, such as blocking back contact or a large “spike”-like conduction band offset (CBO) at the heterojunction interface . The increase of J 0 , the increased carrier recombination, may result from deteriorated material/electronic properties of the CZTSSe absorber in the space charge region (SCR) . It is well-known that carrier recombination usually results from deep-level defects in the CZTSSe absorber. , It was reported that the Sn Zn antisite defects, located near the midgap of the CZTSSe absorber, are particularly harmful recombination centers .…”

“…29 The increase of J 0 , the increased carrier recombination, may result from deteriorated material/electronic properties of the CZTSSe absorber in the space charge region (SCR). 15 It is well-known that carrier recombination usually results from deep-level defects in the CZTSSe absorber. 30,31 It was reported that the Sn Zn antisite defects, located near the midgap of the CZTSSe absorber, are particularly harmful recombination centers.…”

“…14 The PCE of CZTSSe solar cells, stored under ambient laboratory conditions for 10 months, decreased from 6.46 to 3.11%. 15 The decreased PCE mainly results from a decrease in V OC and FF, and J SC was nearly unchanged. A Cu + or Cu 2+ salt is usually adopted as the Cu resource for the CZTSSe solar cell.…”

“…The PCE of 3 MeV proton irradiated CZTSSe solar cells, which were stored in the dark at room temperature, was nearly unchanged after 4 years . The PCE of CZTSSe solar cells, stored under ambient laboratory conditions for 10 months, decreased from 6.46 to 3.11% . The decreased PCE mainly results from a decrease in V OC and FF, and J SC was nearly unchanged.…”

Enhanced Carrier Collection in Cd/In-Based Dual Buffers in Kesterite Thin-Film Solar Cells from Nanoparticle Inks

“…While TFSCs fabricated from a kesterite absorber provide an Earth-abundant and stable energy-harvesting solution, their commercialization has been historically restricted, in part due to their V OC -limiting defect states at both the absorber bulk and absorber/buffer interface. , It was found that substituting the conventional CdS buffer layer with In 2 S 3 in kesterite devices produced an increase in the apparent doping density of the CZTSSe film and a higher built-in voltage arising from a more favorable energy-band alignment at the absorber/buffer interface. − However, any associated gain in V OC was negated by the introduction of photoactive defects at the interface, as reported in our previous work . It is believed that elemental doping due to interdiffusion at absorber/buffer heterojunctions plays an important role in passivating interface defects and determining the kesterite solar cells’ performance. , …”