Bimolecular recombination in methylammonium lead triiodide perovskite is an inverse absorption process
Nature Communications Springer Nature 9 (2018) 293
Abstract:
Photovoltaic devices based on metal halide perovskites are rapidly improving in efficiency. Once the Shockley–Queisser limit is reached, charge-carrier extraction will be limited only by radiative bimolecular recombination of electrons with holes. Yet, this fundamental process, and its link with material stoichiometry, is still poorly understood. Here we show that bimolecular charge-carrier recombination in methylammonium lead triiodide perovskite can be fully explained as the inverse process of absorption. By correctly accounting for contributions to the absorption from excitons and electron-hole continuum states, we are able to utilise the van Roosbroeck–Shockley relation to determine bimolecular recombination rate constants from absorption spectra. We show that the sharpening of photon, electron and hole distribution functions significantly enhances bimolecular charge recombination as the temperature is lowered, mirroring trends in transient spectroscopy. Our findings provide vital understanding of band-to-band recombination processes in this hybrid perovskite, which comprise direct, fully radiative transitions between thermalized electrons and holes.The Route to Nanoscale Terahertz Technology: Nanowire-based Terahertz Detectors and Terahertz Modulators
Institute of Electrical and Electronics Engineers (IEEE) 00 (2018) 1-2
Photocurrent spectroscopy of perovskite solar cells over a wide temperature range from 15 to 350 K
Journal of Physical Chemistry Letters American Chemical Society 2018:9 (2017) 263-268
Abstract:
Solar cells based on metal halide perovskite thin films show great promise for energy generation in a range of environments from terrestrial installations to space applications. Here we assess the device characteristics of the prototypical perovskite solar cells based on methylammonium lead triiodide (CH3NH3PbI3) over a broad temperature range from 15 to 350 K (−258 to 77 °C). For these devices, we observe a peak in the short-circuit current density and open-circuit voltage at 200 K (−73 °C) with decent operation maintained up to 350 K. We identify the clear signature of crystalline PbI2 contributing directly to the low-temperature photocurrent spectra, showing that PbI2 plays an active role (beyond passivation) in CH3NH3PbI3 solar cells. Finally we observe a blue-shift in the photocurrent spectrum with respect to the absorption spectrum at low temperature (15 K), allowing us to extract a lower limit on the exciton binding energy of 9.1 meV for CH3NH3PbI3.Large-area, highly uniform evaporated formamidinium lead triiodide thin-films for solar cells
ACS Energy Letters American Chemical Society 2 (2017) 2799-2804
Abstract:
Perovskite thin-film solar cells are one of the most promising emerging renewable energy technologies because of their potential for low-cost, large-area fabrication combined with high energy conversion efficiencies. Recently, formamidinium lead triiodide (FAPbI3) and other formamidinium (CH(NH2)2) based perovskites have been explored as interesting alternatives to methylammonium lead triiodide (MAPbI3) because they exhibit better thermal stability. However, at present a major challenge is the scale-up of perovskite solar cells from small test-cells to full solar modules. We show that coevaporation is a scalable method for the deposition of homogeneous FAPbI3 thin films over large areas. The method allows precise control over film thickness and results in highly uniform, pinhole-free layers. Our films exhibited a high charge-carrier mobility of 26 cm2 V–1s–1, excellent optical properties, and a bimolecular recombination constant of 7 × 10–11 cm3 s–1. Solar cells fabricated using these vapor-deposited layers within a regular device architecture produced stabilized power conversion efficiencies of up to 14.2%. Thus, we demonstrate that efficient FAPbI3 solar cells can be vapor-deposited, which opens up a pathway toward large-area stable perovskite photovoltaics.Modulation of terahertz polarization on picosecond timescales using polymer-encapsulated semiconductor nanowires
Conference on Lasers and Electro-Optics (CLEO 2017) Optical Society of America 2017-January (2017) 1-2