Carbon-Based CsPbBr₃ Perovskite Solar Cells: All-Ambient Processes and High Thermal Stability

The device instability has been an important issue for hybrid organic–inorganic halide perovskite solar cells (PSCs). This work intends to address this issue by exploiting inorganic perovskite (CsPbBr₃) as light absorber, accompanied by replacing organic hole transport materials (HTM) and the metal electrode with a carbon electrode. All the fabrication processes (including those for CsPbBr₃ and the carbon electrode) in the PSCs are conducted in ambient atmosphere. Through a systematical optimization on the fabrication processes of CsPbBr₃ film, carbon-based PSCs (C-PSCs) obtained the highest power conversion efficiency (PCE) of about 5.0%, a relatively high value for inorganic perovskite-based PSCs. More importantly, after storage for 250 h at 80 °C, only 11.7% loss in PCE is observed for CsPbBr₃ C-PSCs, significantly lower than that for popular CH₃NH₃PbI₃ C-PSCs (59.0%) and other reported PSCs, which indicated a promising thermal stability of CsPbBr₃ C-PSCs

Highly Air-Stable Carbon-Based α‑CsPbI₃ Perovskite Solar Cells with a Broadened Optical Spectrum

Inorganic cesium lead halide perovskites with superb thermal stability show promise to fabricate long-term operational photovoltaic devices. However, the cubic phase (α) of CsPbI₃ with an appropriate band gap is unstable in air. We discover that highly stable α-CsPbI₃ can be obtained in dry air (temperature: 20–30 °C; humidity: 10–20%) by replacing PbI₂ with HPbI₃ in a one-step deposition solution. Furthermore, the band gap of HPbI₃-processed α-CsPbI₃ is advantageously reduced from 1.72 to 1.68 eV due to the existence of tensile lattice strain. By employing such an α-CsPbI₃ film in carbon-based perovskite solar cells (C-PSCs), a power conversion efficiency (PCE) of 9.5% is achieved, which is a record value for the α-CsPbI₃ PSCs without hole transport material. Most importantly, over 90% of the initial PCE is retained for nonencapsulated devices after 3000 h of storage in dry air. Therefore, HPbI₃-based one-step deposition presents a promising strategy to prepare high-performance and air-stable α-CsPbI₃ PSCs

Colloidal Precursor-Induced Growth of Ultra-Even CH₃NH₃PbI₃ for High-Performance Paintable Carbon-Based Perovskite Solar Cells

Carbon-based hole transport material (HTM)-free perovskite solar cells (PSCs) have attracted intense attention due to their relatively high stability. However, their power conversion efficiency (PCE) is still low, especially for the simplest paintable carbon-based PSCs (C-PSCs), whose performance is greatly limited by poor contact at the perovskite/carbon interface. To enhance interface contact, it is important to fabricate an even-surface perovskite layer in a porous scaffold, which is not usually feasible due to roughness of the crystal precursor. Herein, colloidal engineering is applied to replace the traditional crystal precursor with a colloidal precursor, in which a small amount of dimethyl sulfoxide (DMSO) is added into the conventional PbI₂ dimethylformamide (DMF) solution. After deposition, PbI₂(DMSO) adduct colloids (which are approximately tens of nanometers in size) are stabilized and dispersed in DMF to form a colloidal film. Compared with PbI₂ and PbI₂(DMSO) adduct crystal precursors deposited from pure DMF and DMSO solvents, respectively, the PbI₂(DMSO) adduct colloidal precursor is highly mobile and flexible, allowing an ultra-even surface to be obtained in a TiO₂ porous scaffold. Furthermore, this ultra-even surface is well-maintained after chemical conversion to CH₃NH₃PbI₃ in a CH₃NH₃I solution. As a result, the contact at the CH₃NH₃PbI₃/carbon interface is significantly enhanced, which largely boosts the fill factor and PCE of C-PSCs. Impressively, the achieved champion PCE of 14.58% is among the highest reported for C-PSCs