**6. Recent developments on 2d perovskite photovoltaic cells**

The 2d layered perovskites are more advanced and useful than their 3d structures. The unique electroluminescent property of 2d perovskites makes them more

**279**

**Figure 9.**

*Two-Dimensional Materials for Advanced Solar Cells DOI: http://dx.doi.org/10.5772/intechopen.94114*

superior to their 3d counterparts. 2d perovskites structures have large exciton binding energy than 3d structures [130–131]. Due to this fact, 2d perovskite has a high photoluminescence quantum yield (PLQY) with enhanced radiative recombination. The appearance of cascaded energy structures in 2d perovskites films (mixed n layer thickness) leads to a fast and efficient energy transfer from lower-n quantum wells to higher-n quantum wells. These results in the decreased exciton quenching effect: occurring the enhanced van der Walls interactions in organic molecules and hydrophobic organic ligands, 2d perovskites show enhanced and ambient and thermal stability in the comparison with 3d perovskites. In 2d perovskites, the electrical and optical properties can be tuned more and advanced applications like circular-polarized emission and broadband emission due to their excellent chemical tenability [132–135]. You *et al.* [136] developed a novel annealing approach formethylammonium lead iodide (MAPbI3) and (CsPbI3)0.05(FAPbI3)0.95(MAPbBr3)0.05 mixed perovskite

*(a) Schematic illustration of the device and the dual-protection CsPbI2Br film. (b) Band alignment between various layers of a complete device. (c) the J* − *V curves of the devices fabricated from the ref., BT, and BTSTh films. (d) the EQE spectra of the various devices. (e) the stabilized maximum power output of the devices.* 

*Reprinted with permission from [140]. Copyright (2020) American Chemical Society.*

#### *Two-Dimensional Materials for Advanced Solar Cells DOI: http://dx.doi.org/10.5772/intechopen.94114*

*Solar Cells - Theory, Materials and Recent Advances*

28 W cm−2 [128]. The sample (semiconductor plasmon-sensitized nanocomposites i.e. mCu2-xS@SiO2@ Er2O3), which changes the broadband infrared light to visible light by the localized surface plasmon resonance (LSPR) of Cu2-xS integrated with TiO2 paste [129]. This arrangement is used in PSCs as an electron extraction layer with an enhanced response of 800–1000 nm. With the dependency of the power density of the 980 nm extraction layer (>0.85 mAcm−2), the short circuit current

*(a) Photographic image, (b) schematic, (c) low-resolution, (d) high-resolution, and (e) cross-sectional SEM images of SHJ solar cells. (f) J* − *V characteristics of SHJ solar cells with various concentrations of GQDs. (g) EQE spectra of SHJ solar cells without and with 0.3 wt % of GQDs. Reprinted with permission from [116].* 

The 2d layered perovskites are more advanced and useful than their 3d structures. The unique electroluminescent property of 2d perovskites makes them more

**6. Recent developments on 2d perovskite photovoltaic cells**

**278**

**Figure 8.**

density was noticed to rise 45 Wcm−2.

*Copyright (2016) American Chemical Society.*

superior to their 3d counterparts. 2d perovskites structures have large exciton binding energy than 3d structures [130–131]. Due to this fact, 2d perovskite has a high photoluminescence quantum yield (PLQY) with enhanced radiative recombination. The appearance of cascaded energy structures in 2d perovskites films (mixed n layer thickness) leads to a fast and efficient energy transfer from lower-n quantum wells to higher-n quantum wells. These results in the decreased exciton quenching effect: occurring the enhanced van der Walls interactions in organic molecules and hydrophobic organic ligands, 2d perovskites show enhanced and ambient and thermal stability in the comparison with 3d perovskites. In 2d perovskites, the electrical and optical properties can be tuned more and advanced applications like circular-polarized emission and broadband emission due to their excellent chemical tenability [132–135].

You *et al.* [136] developed a novel annealing approach formethylammonium lead iodide (MAPbI3) and (CsPbI3)0.05(FAPbI3)0.95(MAPbBr3)0.05 mixed perovskite

#### **Figure 9.**

*(a) Schematic illustration of the device and the dual-protection CsPbI2Br film. (b) Band alignment between various layers of a complete device. (c) the J* − *V curves of the devices fabricated from the ref., BT, and BTSTh films. (d) the EQE spectra of the various devices. (e) the stabilized maximum power output of the devices. Reprinted with permission from [140]. Copyright (2020) American Chemical Society.*

films by fast laser beam scanning. Under optimum conditions, high-quality perovskite films with good crystallinity, preferred orientation, and low density of defects device offers PCE nearly about 20%. Wang *et al.* [137] showed an efficient strategy to tune the band structure and electron mobility of the ETL by adding NH4Cl to the sol–gel-derived ZnO precursor. Low temperature (160°C) fabricated CsPbIBr2solar cells recorded high efficiency of 10.16%. Li *et al.* [138] fabricated the MAPbI3perovskite solar cells and showed the device performance is strongly influenced by the TiO2 electron transport layer. Oz *et al.* [139] studied the effect of lead(II)propionate additive on the stabilization of CsPbI2Brall-inorganic perovskite, and the use of a novel dopant-freepolymer hole transport material (synthesized by us) for photovoltaic performance assessment of CsPbI2Br solar cells.

Fu and his co-workers report a dual-protection strategy via incorporating monomer trimethylolpropane triacrylate (TMTA) intoCsPbI2Br perovskite bulk and capping the surface with 2-thiophenemethylammonium iodide (Th − NI) [140]. The fabricated devices show a greatly improved efficiency from 12.17 to 15.58% with an opening circuit voltage (Voc) of 1.286 V. **Figure 9a** presents a schematic illustration of the device and the dual-protection CsPbI2Br film. The UPS measurements are conducted to reveal the electronic structure changes the calculated results are drawn in **Figure 9b**. The photocurrent density-voltage (J-V) curves of the optimal devices under AM 1.5 illumination are presented in **Figure 9c.** The ref. device shows the best efficiency of 12.17% with a Voc of 1.151 V, and TMTA doped film (BT) devices show an improved efficiency of 13.88% after incorporating 1 mg/mL of TMTA. In **Figure 9e**, the Th − NI modified BT film (BTSTh) device exhibits the improved output efficiency with 14.93% for 1000 s, while the ref. shows the attenuated efficiency and remains 10.51% under the same operation, which indicates the better operational stability for the BTSTh devices.

Li *et al.* [141] reported vertically aligned 2D/3D Pb − Sn perovskites with enhanced charge extraction and suppressed phase segregation for efficient printable solar cells. Wang *et al.* [142] successfully fabricated high-quality CsPbBr3 films via additive engineering with NH4SCN. The incorporation of NH4 + and pseudohalide ion SCN<sup>−</sup> into the precursor solution, a smooth and dense CsPbBr3 film with good crystallinity and low trap state density can be obtained.
