Nanostructured Perovskite Solar Cells

Abstract

Over the past decade, lead halide perovskites have emerged as one of the leading photovoltaic materials due to their long carrier lifetimes, high absorption coefficients, high tolerance to defects, and facile processing methods. With a bandgap of ~1.6 eV, lead halide perovskite solar cells have achieved power conversion efficiencies in excess of 25%. Despite this, poor material stability along with lead contamination remains a significant barrier to commercialization. Recently, low-dimensional perovskites, where at least one of the structural dimensions is measured on the nanoscale, have demonstrated significantly higher stabilities, and although their power conversion efficiencies are slightly lower, these materials also open up the possibility of quantum-confinement effects such as carrier multiplication. Furthermore, both bulk perovskites and low-dimensional perovskites have been demonstrated to form hybrids with silicon nanocrystals, where numerous device architectures can be exploited to improve efficiency. In this review, we provide an overview of perovskite solar cells, and report the current progress in nanoscale perovskites, such as low-dimensional perovskites, perovskite quantum dots, and perovskite-nanocrystal hybrid solar cells.

Keywords: hybrid solar cells; lead halide solar cells; low-dimensional perovskites; nanocrystal solar cells; organic–inorganic hybrid solar cells; perovskite nanocrystals; perovskite quantum dots; perovskites; solar cells.

Figure 5

Schematic of the proposed contributions to hysteresis. ITO, FTO, ETL and HTL stand for indium-doped tin oxide, fluorine-doped tin oxide, electron transport layer, and hole transport layer, respectively. Reproduced from ref. [76], with permission from Elsevier, 2016.

Figure 1

Cubic perovskite unit cell.

Figure 2

Various device architectures for organometal trihalide perovskite solar cells. (a) Mesoporous sensitized, (b) bi-layer, (c) n-i-p planar and (d) p-i-n planar. ETL, HTL, and TCO stand for electron transport layer, hole transport layer, and transparent conducting oxide, respectively.

Figure 3

Degradation of MAPbI₃. (a) Photographs of MAPbI₃ degradation and (b) corresponding X-ray diffraction (XRD) spectra of the same samples after 1, 13, and 26 days stored in ambient conditions. The starred peaks in the XRD spectra correspond to PbI₂. Reproduced from ref. [30], with permission from John Wiley and Sons, 2016.

Figure 4

(a,b) Current density-voltage curves with forward (R-F) and reverse (F-R) voltage scan direction for a device with hysteresis (a) and without (b). Reproduced from ref. [66], with permission from The Royal Society of Chemistry, 2017. (c,d) Time-dependent photocurrent response under reverse and forward stepped scans with (b) 1 s step time and (c) 0.1 s step time. Reproduced from ref. [67], with permission from American Chemical Society, 2015. (e,f) Current decay after removing device from illumination showing two discharging events occurring over different timescales. Reproduced from ref. [68], with permission from American Chemical Society, 2015.

Figure 6

Overview of the different perovskite dimensionalities. Reproduced from ref. [79], with permission from John Wiley and Sons, 2015.

Figure 7

Reducing the dimensionality of organometal halide perovskites leads to higher stability, but lower device performance. Reproduced from ref. [22], with permission from American Chemical Society, 2016

Figure 8

Solar cells based on a perovskite absorber with a two-dimensional network. (a) Sheets align parallel with the contacts resulting in low carrier mobility between the contacts and (b) sheets align perpendicular to the contacts resulting in favorable out-of-plane mobility between contacts.

Figure 9

2D perovskite solar cells using 3-bromobenzylammonium iodide barrier molecule. (a) Schematic of the device nanostructuring, (b) schematic of the device architecture, (c) energy band alignment relative to the vacuum level in eV, (d) current density-voltage measurement, (e) incident photon conversion efficiency (ICPE), (f) histogram showing reproducibility of the power conversion efficiency (PCE) and (g) solar cell stability for devices stored in the dark between measurements under ≈40 relative humidity. Reproduced with modifications for clarity from ref. [24], with permission from John Wiley and Sons, 2018.

Figure 10

Schematic of the structure of (CH₃NH₃)₃Bi₂I₉ which forms a zero-dimensional network. Bi₂I₉^3- clusters are stabilized within a (CH₃NH₃)⁺ ionic lattice. Reproduced from ref. [82], with permission from Springer Nature, 2017.

Figure 11

CsPbI₃ quantum dot solar cells. (A) Schematic of the device structure, (B) cross-sectional scanning electron microscopy image, (C) current density-voltage scans under solar simulated light, (D) stabilized current at a constant voltage of 0.95 V, and (E) external quantum efficiency. Reproduced from ref. [21], with permission from AAAS, 2017.

Figure 12

Perovskite quantum dot (PQD) solar cells with charge separating heterostructure. (a) Schematic of the device fabrication via spin coating, (b) energy band structure of the various PQDs used in the study, (c) cross-sectional scanning electron microscope of a typical device, (d) the external quantum efficiency (EQE) of solar cells made with various ratios of Cs_0.25Fa_0.75PbI₃ to CsPbI₃ quantum dots, (e) EQE at the absorption edge of various quantum dots in the series Cs_xFA_1-xPbI₃ as the bottom layer. (f) current density-voltage (JV) curves for the devices shown in (d) and (g) stabilized power output (SPO) of the varying compositions shown in (f). Reproduced from ref. [117], with permission from Springer Nature, 2019.

Figure 13

Perovskite-silicon nanocrystal (SiNC) hybrid solar cells show improved device performance especially after light-soaking. (a) Schematic of device structure, and current-density voltage (JV) curves for (b) MAPbI₃ alone, (c) MAPbI₃ with p-type SiNCs, and (d) n-type SiNCs. Reported from ref. [85], with permission from Elsevier, 2018.

Figure 14

Inverted type-I band alignment: (a) electronically coupled and (b) optically coupled. Reproduced from ref. [85], with permission from Elsevier, 2018..

Figure 15

(a) Structure of CaMnO_2.5 reproduced from ref. [141], with permission from American Chemical Society, 2014, (b) optical microscope images of CaMnO_2.5 after laser fragmentation, the inset shows a high-magnification optical microscope image, and (c) current density-voltage characteristic of a CaMnO_2.5 solar cell under solar simulated light.