Functional Materials for Fabrication of Carbon-Based Perovskite Solar Cells: Ink Formulation and Its Effect on Solar Cell Performance

Abstract

Perovskite solar cells (PSCs) have rapidly developed into one of the most attractive photovoltaic technologies, exceeding power conversion efficiencies of 25% and as the most promising technology to complement silicon-based solar cells. Among different types of PSCs, carbon-based, hole-conductor-free PSCs (C-PSCs), in particular, are seen as a viable candidate for commercialization due to the high stability, ease of fabrication, and low cost. This review examines strategies to increase charge separation, extraction, and transport properties in C-PSCs to improve the power conversion efficiency. These strategies include the use of new or modified electron transport materials, hole transport layers, and carbon electrodes. Additionally, the working principles of various printing techniques for the fabrication of C-PSCs are presented, as well as the most remarkable results obtained from each technique for small-scale devices. Finally, the manufacture of perovskite solar modules using scalable deposition techniques is discussed.

Keywords: inkjet printing; metal oxides; nanoinks; nanomaterials; screen printing; spray deposition.

Figure 1

Energy band diagram of various metal oxides used in perovskite solar cells with carbon electrode. Reproduced with permission from Ref. [8].

Figure 2

Conventional PSC (left) and C-PSC (right) working principles upon light illumination. E_fn and E_fp represent the electron and hole quasi-Fermi levels, respectively. Reproduced with permission from Ref. [11].

Figure 3

Schematic view of the spin coating stages (ω is the angular velocity).

Figure 4

(a) X-ray diffraction pattern; (b) Raman spectrum with inset of SEM image of brookite nanorods and TEM image of brookite nanocubes; (c) EQE of the champion devices comparing brookite nanorods and nanocubes with commercial anatase; and (d) IS representation along with the fitted electrical circuit diagrams. Reproduced with permission from Ref. [63].

Figure 5

SEM images of (a) CsPbIBr₂ cell based on F–SnO₂ film; (b) CsPbIBr₂ cell based on NP-SnO₂ film; (c) cross section of CsPbIBr₂ film based on F–SnO₂ film; (d) cross section of CsPbIBr₂ cell based on NP-SnO₂ film; (e) CsPbIBr₂ based on F–SnO₂ film; (f) the light path in the CsPbIBr₂ cell based on NP-SnO₂ film. Reproduced with permission from Ref. [67].

Figure 6

Schematic view of the contact angles of ZnO NPs solution dropped on FTO substrates with DI treatment and without DI treatment and the contact angles of the perovskite precursor solution dropped on ZnO/FTO films with and without DI treatment.

Figure 7

XRD spectra of the CsPbBr₃ films prepared on different ETLs with corresponding SEM image of CsPbBr₃ film grown on Nb₂O₅/FTO and Li: Nb₂O₅/FTO. Reproduced with permission from Ref. [74].

Figure 8

Schematic of perovskite cell fabrication processes using different nanomaterials dispersed in the perovskite layer. (a) B-MWNTs on PbI₂ layer followed by MAPbI₃ perovskite film, reprinted with permission from [78]; Copyright {2017} American Chemical Society. (b) CNPs dispersed in the antisolvent as chlorobenzene; reproduced with permission from Ref. [79].

Figure 9

(a) CQDs dispersed in the antisolvent as ethyl acetate, (b) XPS spectra of EACQDs, (c) deconvolution of C, and (d) XRD image of pristine and 0.01 EACQDs optimized PSCs, reproduced with permission from Ref. [80].

Figure 10

Schematic illustration of the basic principles of screen printing. Reproduced with permission from Ref. [82].

Figure 11

(A) Scheme of fully printable triple-stack mesoporous carbon-based perovskite solar cells (PSC), (B) Band gap diagram of each layer present in the carbon-based PSC, and (C) crystalline structure of MAPbI₃ perovskite. Reproduced with permission from Ref. [86].

Figure 12

(A) Implementation of an extra Al₂O₃ layer with m-TiO₂ and m-ZrO₂ via a vacuum technique, (B) infiltration of perovskite precursor solution through the layers, and (C) energy band diagram of hole-conductor-free C-PSC with Al₂O₃ interlayer. Reproduced with permission from Ref. [96].

Figure 13

XRD analyses of black NiOx acquired from Sigma-Aldrich: (a) powder of NiO, Ni(OH)₂, NiOOH, and Ni₂O₃, and (b) mixture of Ni²⁺ and Ni³⁺.Reproduced with permission from [98].

Figure 14

Cross-section of the perovskite/triple-stack mesoporous carbon-based solar cell with Co₂O₃ hole-transporting layer: (a) low magnification, and (b) high magnification, (c) J-V characteristics of standard carbon cell with an aperture area of 0.09 cm² (under 1 Sun) without and with Co₃O₄ layer, and (d) J-V characteristics of module with an active area of 70 cm² and with Co₃O₄. Reproduced with permission from Ref. [97].

Figure 15

Construction of the: (a) single carbon electrode composed of a mesoporous carbon layer, and (b) double-layer carbon electrode composed of a mesoporous carbon below a conductor carbon layer. Reproduced with permission from Ref. [105].

Figure 16

Working principles of inkjet printers: (a) CIJ; and (b) DOD. Reproduced with permission from Ref [124].

Figure 17

X-ray diffraction (XRD) patterns after infiltrating of CH₃NH₃PbI₃ (MAPI) and annealing. The dominating (101) reflection at 2θ = 25.3° is attributed to anatase TiO₂ (inset). At reduced intensity scale, the characteristic reflections of the cubic phase of the MAPI perovskite crystal are clearly visible (blue squares). The absence of a reflection peak at 2θ = 12.5° reveals that all the precursor ink has been transformed to the hybrid metal halide perovskite and that no un-desirable PbI₂ is present. Reproduced with permission from Ref. [135].

Figure 18

Schematic illustration of the main components in a slot-die processing set-up.

Figure 19

Schematic illustration of the “doctor blade” film deposition process.

Figure 20

UV-Vis absorbance spectra of ZrO₂ film (N_ZrO₂) and double-layered film (DL_ZrO₂) deposited on glass. Reproduced with permission from Ref. [145].

Figure 21

Schematic illustration of the spray coating deposition process.

Figure 22

(a) Performance of 70 cm² mini-module with CsBr-modified TiO₂ layer in comparison with a standard carbon-based perovskite solar cell; (b) Image of a fully printable mini-module. Reproduced with permission from Ref. [4].