Efficiency Potential and Voltage Loss of Inorganic CsPbI₂Br Perovskite Solar Cells

Abstract

Inorganic perovskite solar cells show excellent thermal stability, but the reported power conversion efficiencies are still lower than for organic–inorganic perovskites. This is mainly caused by lower open‐circuit voltages (VOCs). Herein, the reasons for the low VOC in inorganic CsPbI2Br perovskite solar cells are investigated. Intensity‐dependent photoluminescence measurements for different layer stacks reveal that n–i–p and p–i–n CsPbI2Br solar cells exhibit a strong mismatch between quasi‐Fermi level splitting (QFLS) and VOC. Specifically, the CsPbI2Br p–i–n perovskite solar cell has a QFLS–e ·VOC mismatch of 179 meV, compared with 11 meV for a reference cell with an organic–inorganic perovskite of similar bandgap. On the other hand, this study shows that the CsPbI2Br films with a bandgap of 1.9 eV have a very low defect density, resulting in an efficiency potential of 20.3% with a MeO–2PACz hole‐transporting layer and 20.8% on compact TiO2. Using ultraviolet photoelectron spectroscopy measurements, energy level misalignment is identified as a possible reason for the QFLS–e ·VOC mismatch and strategies for overcoming this VOC limitation are discussed. This work highlights the need to control the interfacial energetics in inorganic perovskite solar cells, but also gives promise for high efficiencies once this issue is resolved.

Lead halide coordination competition at buried interfaces for low VOC-deficits in wide-bandgap perovskite solar cells

“…[23][24][25][26][27] The V OC deficit of WBG PSCs (Z0.5 V) is unprecedentedly much larger than that of conventional bandgap and narrow-bandgap (NBG) solar cells (B0.3 V). This is mainly due to the following aspects: (1) non-radiative recombination caused by defects and energy level mismatch at the interface between WBG perovskites and charge selective layers; 10,23,28,29 (2) WBG perovskites have large bulk defects due to their fast crystallization rate; 14 and (3) the optoelectronic characteristics of hole selective layers and their influence on perovskite crystallization.…”

Mixed‐Halide Inorganic Perovskite Solar Cells: Opportunities and Challenges

“…Specifically, the bandgap of CsPbI 3− x Br x is concentrated in the wide bandgap range, consistent with the spectrum range of indoor light sources. [ 56 ] Therefore, CsPbI 3− x Br x absorbers are typically used for indoor PV devices. In this review, we systematically compared and summarized the recent indoor PV based on mixed‐halide inorganic PSCs.…”

Interface Modification for Energy Level Alignment and Charge Extraction in CsPbI3 Perovskite Solar Cells

“…In CsPbI 3 -based PSCs, phase stability at the operating temperature and the crystallization processes are the main challenges associated with device fabrication. , Recently, organic precursors, e.g. hydrogen lead iodide “HPbI 3 ” and dimethylammonium iodide (DMAI), assisted film growth, and molten salt additive based strategies have been adopted to address these challenges. − Besides, for all compositions open circuit voltage loss (defined as E g – eV oc, where E g is the optical band gap of the absorber, e is the elementary charge, and V oc is the measured open circuit voltage of the device) is higher in inorganic perovskite solar cells than in organic–inorganic solar cells . To date, over 21% efficiency has been achieved so far for CsPbI 3 with a V oc of over 1.2 V and a minimum open circuit voltage deficit ( V loss ) of 0.46 V, and thereby inorganic perovskite solar cells have a large open circuit voltage deficit as compared to organic–inorganic halide perovskite solar cells with a minimum V loss of ∼0.3 V .…”

“…To date, over 21% efficiency has been achieved so far for CsPbI 3 with a V oc of over 1.2 V and a minimum open circuit voltage deficit ( V loss ) of 0.46 V, and thereby inorganic perovskite solar cells have a large open circuit voltage deficit as compared to organic–inorganic halide perovskite solar cells with a minimum V loss of ∼0.3 V . Currently, inorganic perovskite film post-treatment methods have been very effective in increasing open-circuit voltage values. − However, the energy level misalignment between the inorganic perovskite layer and the charge-selective contacts requires interfacial engineering to resolve the open circuit voltage deficit. ,, …”

“…17−19 However, the energy level misalignment between the inorganic perovskite layer and the charge-selective contacts requires interfacial engineering to resolve the open circuit voltage deficit. 14,20,21 An inorganic perovskite has a flat band surface, and introducing a surface band bending has been proven to be favorable for charge extraction. 22,23 Canil et al 24 systematically studied how the Fermi-level of perovskite with (Cs 0.05 [MA 0.15 FA 0.85 PbI 0.85 Br 0.15 ] 0.95 ) composition can be tuned by the treatment of dipole molecules on the perovskite surface.…”