It is proved that secondary phases, such as Cu 2 Se, and ZnSe etc., and MoSe 2 layer can form at Cu 2 ZnSn(S,Se) 4 (CZTSSe)/Mo electrode interface, due to that Mo electrode reacts with CZTSSe and Se vapor during selenization process. The secondary phases and MoSe 2 with inappropriate thickness can decrease power conversion efficiency (PCE) of CZTSSe solar cell. In this work, a simple method was proposed to suppress the reaction between CZTSSe and Mo, and to optimize the thickness of MoSe 2 . This was achieved by growing a layer of Mo oxide in situ on the Mo electrode surface through soaking the Mo electrode in H 2 O 2 . The Mo oxide layer consisted of MoO 3 , MoO x and MoO 2 . It could suppress the reaction between Mo and CZTSSe, thus preventing the formation of secondary phases in CZTSSe. By further tuning the soaking time, the thickness and density of the Mo oxide layer were optimized, resulting in an optimized thickness of the MoSe 2 layer and a significant improvement in the contact quality at both the front and back interfaces. This improvement is beneficial for suppressing carrier recombination and reducing contact resistance. Furthermore, the Cu/(Zn+Sn) ratio in CZTSSe was optimized, leading to an expansion of the depletion region width. As a result, the reverse saturation current density and series resistance decrease, while the photogenerated current density increases. This ultimately led to a rise in PCE from 7.66% for CZTSSe solar cells with Mo electrodes that were not soaked to 8.95% for those with Mo electrodes soaked for 20 s.
Jinhui Zhang,Chuanhe Ma,Haixuan Gao,Jinchun Jiang,Hailong Wang
An over-thick MoSe2 layer and numerous voids at the absorbing layer inside and backside lead to a relatively low Jsc and PCE of CZTSSe solar cells. In previous studies, MoO2 and MoO3 sacrificial layers have been commonly used to eliminate those voids and reduce the thickness of MoSe2 layers. However, there is still no clarity about which one is more effective. In this work, we prepared MoO2 and MoO3 sacrificial layers on the surface of Mo-coated SLG substrates by air annealing and ammonia (NH3·H2O) etching, respectively. J–V testing shows that both MoO2 and MoO3 can effectively improve the Jsc and PCE of CZTSSe solar cells, wherein MoO3 is more effective. Comparative analysis shows that the electrical mechanism of Jsc and PCE improvement lies in the significant reduction of device series resistance (Rs). SEM images and XRD pattern results indicate that the reason for Rs decreasing is void elimination and MoSe2 layer thickness reduction from 600 nm to 270 nm after applying MoO3. With the aid of the MoO3 sacrificial layer, the PCE of the CZTSSe device increases from 7.51% to 9.58% (total area 0.21 cm2) without the MgF2 anti-reflection layer.
Antimony sulfide (Sb 2 S 3 ) with a 1D molecular structure has strong bending characteristics, showing great application potential in flexible devices. Herein, the flexible substrate-structured Sb 2 S 3 solar cells is developed and improve device performances by the back interface selenization. The high-quality Sb 2 S 3 film with an optimal thickness of 1.8 µm, ensuring efficient spectra utilization, is deposited on flexible Mo foils by the rapid thermal evaporation technique. To solve the issues of back interfacial recombination and charge transport, the 20 nm MoSe 2 layer between Sb 2 S 3 film and Mo foil is fabricated by substrate selenization in the tube furnace. Further investigations indicate that the MoSe 2 layer improves the interfacial energy band alignments and induces the [hk1] orientation of Sb 2 S 3 film, thereby passivating defects and enhancing the carrier transport capacity. The flexible solar cell in the structure of Mo foil/MoSe 2 /Sb 2 S 3 /CdS/ITO/Ag, exhibiting good flexibility to stand thousands of bending, achieves an efficiency of 3.75%, which is the highest for Sb 2 S 3 devices in substrate configuration. The presented flexible structure and back interfacial selenization study will provide new prospects for inorganic Sb 2 S 3 thin film solar cells.
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