In Situ Constructing Intermediate Energy‐Level Perovskite Transition Layer for 15.03% Efficiency HTL‐Free Carbon‐Based Perovskite Solar Cells with a High Fill Factor of 0.81

Abstract

Hole transporting layer (HTL)‐free, all‐inorganic CsPbX3 (X: I, Br, or mixed halides), carbon‐based perovskite solar cells (C‐PSCs) show promising prospect for photovoltaic application due to their low cost, excellent stability, and theoretical high efficiency. However, the inefficient hole extraction of the carbon electrode and relatively narrow light absorption range of inorganic perovskite limit the power conversion efficiency (PCE) of this kind of PSCs. Herein, these issues are addressed through in situ constructing of an intermediate energy‐level perovskite transition layer between CsPbI2.2Br0.8 and the carbon electrode via a facile formamidinium iodide (FAI) posttreatment strategy. It is demonstrated that the (CsFA)PbI3–xBrx film is in situ formed atop inorganic perovskite due to the ions exchange between FAI and CsPbI2.2Br0.8, which can not only broaden the light absorption edge of CsPbI2.2Br0.8 from 657 to 680 nm, but also serve as a hole transfer highway between CsPbI2.2Br0.8 and the carbon electrode, mainly due to its suitable intermediate energy‐level and effective defect passivation. Consequently, the optimized HTL‐free C‐PSC achieves a champion PCE of 15.03% with an ultrahigh fill factor of 0.81. Besides, the stability of CsPbI2.2Br0.8 film (especially under humid environment) and corresponding C‐PSC are also improved.

Surface Passivation of CsPbI 3 Films for Efficient and Stable Hole-Transporting Layer-Free Carbon-Based Perovskite Solar Cells

“…But for the commercial application of PSCs, long-term stability is as equally important as device efficiency. Till now, highly efficient PSCs are based on organic–inorganic hybrid perovskites, which consist of thermolabile organic cations (e.g., methylammonium (MA), formamidinium (FA)), hindering their further development for commercialization. − To address this issue, inorganic perovskites employing Cs + as an A-site cation are developed, which have been demonstrated to be an efficient component for constructing highly efficient PSCs. − Among all of the reported inorganic perovskites, the CsPbI 3 perovskite possesses a suitable band gap ( E g : ∼1.7 eV) as well as decent phase stability and is considered as the most promising candidate for commercial application. − Actually, the PCE of the best-performing CsPbI 3 -based PSCs has exceeded 21% and is in a rapid growth stage currently. , …”

Bidirectional Modification of Buried Interface Reduces Energy Loss for Planar Perovskite Solar Cells with Efficiency >23%

“…[ 25 ] Dark I – V curves shown in Figure 6c reveal that the reverse current of target PSC under dark condition is lower than that of control device, indicating that more photo‐generated carriers pass through the device rather than direct shunting along with the defect‐assisted channels. [ 26 ] Then, to make a quantitative analysis of the trap‐state density for SnO 2 /perovskite and SnO 2 /NiAc 2 /perovskite samples, space‐charge‐limited current (SCLC) measurement was carried out using electron‐only devices with the structure of ITO/SnO 2 with or without NiAc 2 /perovskite/[6,6]‐phenyl‐C 61 ‐butyric acid methyl ester (PCBM)/Ag, as shown in Figure 6d [8a] . Here, the trap‐filled limit voltage ( V TFL ) for target device shows evident decline in comparison with control device.…”

Carbon-based perovskite solar cells with electron and hole-transporting/-blocking layers

“…In addition, the transition layer can also serve as a hole transfer channel between CsPbI 2.2 Br 0.8 and the carbon electrode due to its suitable intermediate energy level and effective defect passivation. As a result, the optimized CPSC achieves a champion PCE of 15.03% and an ultrahigh FF of 0.81, and the stability of the device is also improved (figure 4(f)) [64].…”

“…Similar to the buried interface, the main problems to be solved for the upper interfaces of CPSCs are poor contact due to the rough surface of the perovskite and carbon electrodes, poor hole extraction and transport ability, severe surface defects resulting in non-radiative recombination at the interface, and energy-level mismatch between the layers. As a result, researchers have used organic polymers [54][55][56][57], organic salts [58][59][60][61][62][63][64][65][66], inorganic materials [67,68], and carbon nanotubes [12,69,70] for interface engineering to improve the quality of the interface, enhance the film crystallinity quality of perovskite, passivate interfacial defects, improve the interfacial energy band alignment, enhance the interfacial contact, build a hole transfer channel and act as an EBL to reduce the carrier non-radiative recombination, and accelerate the hole extraction and transfer at the interface.…”