Abstract
Inorganic mixed‐halide CsPbX3‐based perovskite solar cells (PeSCs) are emerging as one of the most promising types of PeSCs on account of their thermostability compared to organic–inorganic hybrid counterparts. However, dissatisfactory device performance and high processing temperature impede their development for viable applications. Herein, a facile route is presented for tuning the energy levels and electrical properties of sol–gel‐derived ZnO electron transport material (ETM) via the doping of a classical alkali metal carbonate Cs2CO3. Compared to bare ZnO, Cs2CO3‐doped ZnO possesses more favorable interface energetics in contact with the CsPbI2Br perovskite layer, which can reduce the ohmic loss to a negligible level. The optimized PeSCs achieve an improved open‐circuit voltage of 1.28 V, together with an increase in fill factor and short‐circuit current. The optimized power conversion efficiencies of 16.42% and 14.82% are realized on rigid glass substrate and flexible plastic substrate, respectively. A high thermostability can be simultaneously obtained via defect passivation at the Cs2CO3‐doped ZnO/CsPbI2Br interface, and 81% of the initial efficiency is retained after aging for 200 h at 85 °C.
Highlights
CsPbI3 in cubic crystal structure benefits the sufficient absorption of visible light due to the smallest optical bandgap (Eg) ofMetal halide perovskite solar cells (PeSCs) have attracted tre- ≈1.73 eV (α-phase)
It is noted that there is no significant difference in surface morphology among these samples, and the uniform structures rule out the doping influence on the growth of ZnO films
These results demonstrate that the Cs2CO3 doping can effectively suppress the phase transformation of CsPbI2Br, which might originate from the defect passivation effect of Cs2CO3 on CsPbI2Br crystal surface for improving the long-term stability
Summary
CsPbI3 in cubic crystal structure benefits the sufficient absorption of visible light due to the smallest optical bandgap (Eg) of. CsPbBr3 with small Br− ions shows the superior phase stability, while its wide Eg of ≈2.3 eV restricts the light-harvesting capacity in the visible light region.[18–21] In this regard, the compositional optimization of all-inorganic CsPbX3 perovskites indicates that mixed-halide CsPbI2Br with a suitable Eg of ≈1.92 eV may balance the light-harvesting efficiency and structural stability under ambient conditions for achieving highly efficient and stable PeSCs.[11,21–24]. The energy level of ZnO can be tuned by introducing organic or inorganic materials as a dopant,[35,36] which benefits the addressing of energy level offset issue in PeSCs. In particular, the use of alkali metal compounds is an effective n-type doping method due to the advantages of the enhanced electrical properties, ease of material handling, and operational stability.[37]. A high thermostability can be simultaneously obtained via defect passivation at the ZnO:Cs2CO3/CsPbI2Br interface, and the optimized devices retain 96% and 81% of their initial efficiencies after aging for 200 h at room temperature and 85 °C, respectively
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