State-of-the-Art Perovskite Solar Cells Benefit from Photon Recycling at Maximum Power Point

Photon recycling is required for a solar cell to achieve an open-circuit voltage ($V_{OC}$) and power conversion efficiency (PCE) approaching the Shockley-Queisser theoretical limit. In metal halide perovskite solar cells, the achievable performance gains from photon recycling remain uncertain due to high variability in perovskite material quality and the non-radiative recombination rate ($k_{1}$). In this work, we study state-of-the-art $\textrm{Cs}_{0.05}(\textrm{MA}_{0.17}\textrm{FA}_{0.83})_{0.95}\textrm{Pb}(\textrm{I}_{0.83}\textrm{Br}_{0.17})_{3}$ films and analyze the impact of varying non-radiative recombination rates on photon recycling and device performance. Importantly, we predict the impact of photon recycling at the maximum power point (MPP), demonstrating an absolute PCE increase of up to 2.0% in the radiative limit, primarily due to a 77 mV increase in $V_{MPP}$. Even with finite non-radiative recombination, benefits from photon recycling can be achieved when non-radiative lifetimes and external LED electroluminescence efficiencies measured at open-circuit, $Q_{e}^{LED}(\textrm{V}_{OC})$, exceed 2 $\mu$s and 10%, respectively. This analysis clarifies the opportunity to fully exploit photon recycling to push the real-world performance of perovskite solar cells toward theoretical limits.Comment: Main text: 16 pages and 6 figures, SI: 22 pages and 21 figure

Slowed Recombination via Tunable Surface Energetics in Perovskite Solar Cells

Metal halide perovskite semiconductors have the potential to reach the optoelectronic quality of meticulously grown inorganic materials, but with a distinct advantage of being solution processable. Currently, perovskite performance is limited by charge carrier recombination loss at surfaces and interfaces. Indeed, the highest quality perovskite films are achieved with molecular surface passivation, for example with n-trioctylphosphine oxide, but these treatments are often labile and electrically insulating. As an alternative, the formation of a thin 2D perovskite layer on the bulk 3D perovskite reduces non-radiative energy loss while also improving device performance. But, thus far, it has been unclear how best to design and optimize 2D/3D heterostructures and whether critical material properties, such as charge carrier lifetime, can reach values as high as ligand-based approaches. Here, we study perovskite devices that have exhibited power conversion efficiencies exceeding 25% and show that 2D layers are capable of pushing beyond molecular passivation strategies with even greater tunability. We set new benchmarks for photoluminescence lifetime, reaching values > 30 {\mu}s, and perovskite/charge transport layer surface recombination velocity with values < 7 cm s^{-1}. We use X-ray spectroscopy to directly visualize how treatment with hexylammonium bromide not only selectively targets defects at surfaces and grain boundaries, but also forms a bandgap grading extending > 100 nm into the bulk layer. We expect these results to be a starting point for more sophisticated engineering of 2D/3D heterostructures with surface fields that exclusively repel charge carriers from defective regions while also enabling efficient charge transfer. It is likely that the precise manipulation of energy bands will enable perovskite-based optoelectronics to operate at their theoretical performance limits.Comment: Main text: 15 pages, 4 figures. Supporting Information: 31 pages, 19 figure

Light-Matter Interactions in High-Efficiency Photovoltaics, Light-Emitting Devices, and Strongly Coupled Microcavities

The interactions of light and matter drive many of today’s devices, from electricity generation and consumption to manipulation. Within electricity generation, emerging thin film photovoltaics now rival traditional silicon-based solar cells in terms of power conversion efficiency (PCE) due to dramatic improvements to optoelectronic material properties and device architectures. Within electricity consumption, quantum dot light emitting diodes (QD-LEDs) are a high-efficiency, high color purity, versatile material candidate. Recent efforts to develop heavy metal-free QD-LEDs have led to high external quantum efficiencies in InP- and ZnSebased QDs rivaling the performance of the colloidal archetype of Cd-based QD-LEDs. Within energy manipulation, the emergence of photonics from electronics presents opportunities to engineer low-loss, low-threshold information transmission and computation by all-optical means and matter-mediated hybrid electronic/photonic processes. In this work, we investigate light-matter interactions in emerging thin film perovskite photovoltaics, heavy metal-free QD-LEDs and microcavities, and two-dimensional perovskite microcavity exciton-polaritons. First, we quantify the PCE enhancements due to photon recycling in high-efficiency Cs₀.₀₅(MA₀.₁₇FA₀.₈₃)₀.₉₅Pb(I₀.₈₃Br₀.₁₇)₃ (triple-cation) perovskite thin film photovoltaics as a function of material properties such as non-radiative recombination and the probability of photon escape. We determine that a perovskite active layer material with non-radiative rates k₁< 1x10⁴ s⁻¹ can result in practical PCE improvements of up to 1.8% due to photon recycling alone, and present material and device design principles to harness photon recycling effects in next-generation perovskite solar cells. Next, we investigate energy and charge transfer in InP/ZnSe/ZnS QD thin films and QDLEDs as a function of increasing electric field strength. We probe the voltage-controlled photoluminescence (PL) modulation of a QD-LED in reverse bias and achieve 87% PL quenching, which is, to our awareness, the highest reported quenching efficiency in InP-based QDs. We also demonstrate amplified spontaneous emission processes in QD metallic microcavities by spectral coincidence of a three-dimensional confined photon mode and photon recycling-enhanced gain region. Finally, we form exciton-polaritons (polaritons) at room-temperature in 2D perovskite microcavities resulting in, to the best of our knowledge, a record exciton-photon coupling strength for planar (C₆H₅(CH₂)₂NH₃)₂PbI₄ microcavities of ℏΩ subscript Rabi = 260 ± 5 meV. By utilizing wedged microcavities in which the cavity detuning is changed as a function of excitation position, we probe the temperature-dependent polariton photophysics for varying polariton exciton/photon character. In this way, we reveal material-specific polariton relaxation mechanisms and intracavity pumping schemes from the interplay of 2D perovskite excitonic states.Ph.D