Can photoluminescence quenching be a predictor for perovskite solar cell efficiencies?

Graphite-Based Localized Heating Technique for Growing Large Area Methylammonium Lead Bromide Single Crystalline Perovskite Wafers and Their Charge Transfer Characteristics

Development of a reproducible technique to grow large area single crystalline perovskite wafers is an open research gap in the field of single crystalline perovskite solar cells. A graphite-based localized heating technique for growing large area methylammonium lead bromide (CH3NH3PbBr3; MAPBr) single crystalline thin film (SCTF) on different buffer layers, such as glass/indium doped tin oxide (ITO), glass/ITO/poly(triaryl amine) (PTAA), and glancing angle deposition (GLAD) coated glass/ITO/TiO2 substrates is reported, and their charge transport properties are discussed. It is observed that the localized heating technique can confine the supersaturation of the precursor mainly to the center of the substrate, leading to a restricted number of nucleations within a specific area on the substrate. Here, such 2-3 seed crystals obtained initially are allowed to grow to a larger size of up to 65 mm2. The X-ray diffraction (XRD) analysis indicated that the large area SCTF is an actual single crystal and not a heterogeneous group of small crystals merged together with a crystallinity index (CI) of 92.60 ± 0.11% which was comparable to that of the bulk single crystal (97.74 ± 0.47%). The atomic force microscopy (AFM) image depicted a smooth SCTF surface (R a = 4.37 ± 0.01 nm), and the wave-like pattern is attributed to the substrate morphology, implying that the topography of the substrate plays a crucial role in obtaining a planar SCTF. The XRD, UV-visible, photoluminescence (PL), Raman, and FTIR spectra analyses revealed that the large area SCTF is phase pure and free of residual impurities. The charge injection characteristics of the SCTFs grown on different buffer layers were investigated using PL emission (PLE) and PL decay analyses. The decrease in the PLE intensity for the SCTFs grown on PTAA and TiO2 substrates implied exciton quenching behavior, indicating the injection of the photogenerated charge carriers into the charge transfer layers (CTLs). The decrease of the fast decay component from τ1 = 4.77 ± 0.18 ns for glass to τ1 = 3.32 ± 0.07 ns for TiO2 and τ1 = 3.15 ± 0.33 ns for PTAA is ascribed to the interfacial recombination of the charges accumulated at the CTL/perovskite interface. These results propose that the localized heating technique can be employed for growing large area single crystalline perovskite wafers for optoelectronic and photovoltaic device applications.

Nanostructure and Photovoltaic Potential of Plasmonic Nanofibrous Active Layers

Nanofibrous active layers offer hierarchical control over molecular structure, and the size and distribution of electron donor:acceptor domains, beyond conventional organic photovoltaic architectures. This structure is created by forming donor pathways via electrospinning nanofibers of semiconducting polymer, then infiltrating with an electron acceptor. Electrospinning induces chain and crystallite alignment, resulting in enhanced light-harvesting and charge transport. Here, the charge transport capabilities are predicted, and charge separation and dynamics are evaluated in these active layers, to assess their photovoltaic potential. Through X-ray and electron diffraction, the fiber nanostructure is elucidated, with uniaxial elongation of the electrospinning jet aligning the polymer backbones within crystallites orthogonal to the fiber axis, and amorphous chains parallel. It is revealed that this structure forms when anisotropic crystallites, pre-assembled in solution, become oriented along the fiber- a configuration with high charge transport potential. Competitive dissociation of excitons formed in the photoactive nanofibers is recorded, with 95%+ photoluminescence quenching upon electron acceptor introduction. Transient absorption studies reveal that silver nanoparticle addition to the fibers improves charge generation and/or lifetimes. 1 ns post-excitation, the plasmonic architecture contains 45% more polarons, per exciton formed, than the bulk heterojunction. Therefore, enhanced exciton populations may be successfully translated into additional charge carriers.

Passivation of 2D Cs2PbI2Cl2 Nanosheets for Efficient and Stable CsPbI3 Quantum Dot Solar Cells

Inorganic CsPbI3 perovskite quantum dots (PQDs) possess remarkable optical properties, making them highly promising for photovoltaic applications. However, the inadequate stability resulting from internal structural instability and the complex external surface chemical environment of CsPbI3 PQDs has hindered the development of CsPbI3 PQD solar cells (PQDSCs). In this work, the capping layer composed of inorganic two-dimensional (2D) Ruddlesden-Popper (RP) phase Cs2PbI2Cl2 nanosheets (NSs) is introduced, which may be effectively treated to improve the surface properties of the CsPbI3 PQD film. This modification serves to passivate defects by filling cesium and iodine vacancies while optimizing the energy band arrangement and preventing humidity intrusion, leading to the meliorative stability and photovoltaic performance. The optimized CsPbI3 PQDSCs achieve an enhanced power conversion efficiency (PCE) of 14.73%, with the superb stability of only a 16% efficiency loss after being exposed to ambient conditions (30 ± 5% RH) for 432 h.

The Scale Effects of Organometal Halide Perovskites

Organometal halide perovskites have achieved great success in solution-processed photovoltaics. The explorations quickly expanded into other optoelectronic applications, including light-emitting diodes, lasers, and photodetectors. An in-depth analysis of the special scale effects is essential to understand the working mechanisms of devices and optimize the materials towards an enhanced performance. Generally speaking, organometal halide perovskites can be classified in two ways. By controlling the morphological dimensionality, 2D perovskite nanoplatelets, 1D perovskite nanowires, and 0D perovskite quantum dots have been studied. Using appropriate organic and inorganic components, low-dimensional organic-inorganic metal halide hybrids with 2D, quasi-2D, 1D, and 0D structures at the molecular level have been developed and studied. This provides opportunities to investigate the scale-dependent properties. Here, we present the progress on the characteristics of scale effects in organometal halide perovskites in these two classifications, with a focus on carrier diffusion, excitonic features, and defect properties.