Thin Films of Sn Perovskites: Comparison
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Please note this is a comparison between Version 2 by Beatrix Zheng and Version 1 by Wafa Abdelkareem Ayaydah.

Compared to Pb-based perovskites solar cells (PSCs, TPSCs), tin-based perovskite solar cells (TPSCs) exhibit a much lower PCEpower conversion energy (PCE), mainly due to the poor film quality, correlated degradation, and detrimental effects. Perovskite films are often fabricated from solutions due to ease of fabrication. In order to create a high-performance tin-based PSC, it is imperative to form dense, compact, well-crystalline perovskite films. Many ways have been proposed to resolve the instabilities of tin-based perovskites. The first step to enhance the stability of the device is to gain a deeper understanding of the degradation mechanisms. Earlier, wethe researchers briefly pointed out the effects of moisture, oxygen, illumination, ion migration, and chemical reactions which are the most common causes of degradation in perovskite halides.

  • tin perovskites
  • stability
  • power conversion efficiency

1. Tin Perovskites with Additives/Reducing Agents

A defect is often induced by the fast oxidation of Sn+2 due to its fast kinetics of nucleation and growth in perovskites; therefore, additives that often reduce the fast oxidation and improve the film morphology (compactness) are required. Sn halides (SnF2, SnCl2, SnBr2, and SnI2) and several organic molecules have been shown to prevent oxidation and enhance the performance of TPSCs. Furthermore, Sn halide additives are able to compensate for Sn vacancies in the films, improving the film morphology, reducing the likelihood of vacancy formation, and reducing the background hole density [104][1].

1.1. SnF

2

Additive

One of the first reports of reducing agents was implemented in 2012 by Chung et al. [24][2] using CsSnI3 Sn perovskites as an HTM by doping with SnF2 in dye-sensitized solar cells, which helped in producing a VOC of 0.42 V and an overall PCE of 0.9%. Following this, in 2014 Kumar et al. [105][3] found that incorporating SnF2 into CsSnI3 reduces the formation energy of Sn vacancies, leading to less conductivity in CsSnI3, and as a result, the TPSCs gained a high current density (JSC) of 22 mA cm−2. The impacts of SnF2 doping in FASnI3 with 20% mole were confirmed with X-ray diffraction (XRD) data that indicated a reduced amount of Sn+4 [42][4]. This helped the current density to increase by 10 mA cm−2. In 2018, Xiao et al. [106][5] were able to achieve homogeneous crystal growth and uniform film coverage. They demonstrated that SnF2 can reduce Sn vacancy (VSn) concentrations by boosting their formation energy. Following that, Hartmann et al. [107][6] studied the electronic structure of CsSnBr3 and observed that Sn oxidation was inhibited by the addition of 20% mole SnF2. In 2016, Ma et al. [26][7] showed that SnF2 had the effect of a distinguishable increase in carriers’ lifetime from 0.7 ns to 6 ns. Additionally, hole diffusion length was estimated to increase substantially, as a result of the addition of SnF2, whereas the electron diffusion length remained unchanged. SnF2 is commonly used in most tin-based photovoltaic systems for easy optimization of Sn perovskites.

1.2. SnCl

2

Additive

An additional reducing agent commonly used in Sn perovskites is SnCl2 [108][8]. It was used to increase the stability of the Sn-based devices in an HTM free structure. Using X-ray photoemission spectroscopy (XPS) analysis on CsSnI3 perovskite samples treated with the addition of 10 mol% of SnCl2, they found that SnCl2 was present at the perovskites’ surfaces, and that the SnCl2 layer could act as a dryer to improve the stability of CsSnI3. Interestingly, after 5 months of storage under a nitrogen environment, the PCE was observed to increase, along with the VOC and FF. This improvement in the performance over time can be explained by the SnCl2 doping on the electron-transport layer of the used ETM (i.e., PCBM). In addition, they evaluated different tin halide additives (SnCl2, SnBr2, SnI2, and SnF2) to see how they could affect HTM-free TPSCs (ITO/CsSnI3/PC61BM/BCP/Al). Among the tested devices, with the SnCl2 additive, a PCE of 3.56% was the best, and SnCl2 resulted in the highest film stability. Performance improvements may be attributable to the enhancement of PCBM ETM crystallization under light illumination.

1.3. Hydrazine Additive

Hydrazine has long been used in chemical synthesis to prevent oxidation (reducing agent). Additionally, hydrazine’s highly volatile nature makes it an easy agent to be introduced as a reducing atmosphere. Song et al. [60][9] introduced hydrazine vapor atmosphere prior to the spin-coating process of the perovskite precursor. The films were formed in hydrazine atmosphere resulting in reduced defects, oxidation, and therefore better performance. Similarly, Kayesh et al. [109][10] were able to minimize the concentration of Sn+4 by 20% and significantly suppress carrier recombination during the fabrication of FASnI3 perovskite films, by incorporating hydrazinium chloride (N2H5Cl) into a single precursor solvent system. A high PCE with significantly enhanced VOC and pinhole-free FASnI3 perovskite films were achieved. Li et al. [110][11] reported a solution–deposition method for the fabrication of MASnI3 that included hydrazinium iodide (N2H5I) with SnI2 precursor. A mesoporous TPSC with a PCE of 7.13% was achieved.

1.4. Acidic Additives

Hypophosphorous acid (HPA). In the synthesis of tin-based perovskites, HPA has long been used as a common reducing agent. In most circumstances, HPA is utilized as an assisting reducing agent in antioxidation when powerful agents such as hydroiodic acid (HI) or SnF2 are present, eventually stabilizing the process. Researchers used HPA as a coordinating agent in the CsSnIBr2 production process, which allowed them to speed nucleation while restricting Sn+2 oxidation. Charge carrier density and Sn vacancy levels were lowered as a result of the HPA integration [111][12].
2,2,2-trifluoroethylamine hydrochloride (TFEACl). In combination with SnF2, 5 mol% of TFEACl was found to improve and enhance FASnI3 solar cells [100][13]. The work function of perovskite films may be adjusted by adding Cl. Therefore, the perovskite films are better aligned with the charge transport layers. In addition, light soaking stability was found to be improved, which all resulted in improved device performance and charge collection.
Gallic acid (GA).Wang et al. [112][14] used the antioxidant GA as an additive together with excess SnCl2. GA was found capable to form a complex with SnCl2 that is evenly distributed on perovskite grains. The characteristics of the GA can be derived from the aromatic ring’s hydroxyl groups (–OH), which can donate electrons and absorb oxygen by hydrogen atoms. The SnCl2 layers present atop perovskite grains were expected to result in a wider bandgap compared to the bulk. After 1000 h of air exposure, unencapsulated GA-based devices preserved more than 80% of their initial PCE, which is one of the highest reports. Moreover, the solar cells with GA exhibited a high PCE of 9.03%.
Ascorbic acid (AA). It is a simple but effective additive that inhibits the oxidation of Sn+2 also regulates its film crystallization and creation, and can be utilized to build polymer-stabilized Pb/Sn binary PSCs [113][15], enhancing the optoelectronic quality of dual, perovskite films greatly. The resulting MA0.5FA0.5Pb0.5Sn0.5I3 film’s photogenerated carrier lifetime (183 ns) demonstrates this. As a result, MA0.5FA0.5Pb0.5Sn0.5I3 treated with AA achieved a high PCE of 14.01% and a higher stability than the control device employing the SnF2 additive, outperforming it. This research proposes a novel method for improving the performance and obtaining more stable Pb/Sn-PSCs.

2. Surface Modifiers

There are many surface modifiers for TPSCs that are applied using different methods and can be applied before or after the perovskite layer deposition. Controlling the surface terminations can majorly affect the stability and morphology [59,114,115][16][17][18].
One of the common examples is the introduction of antioxidant-carrying 4-fluorobenzohydrazide (FBH) on top of FASnI3 perovskite films [116][19]. The C=O group in such modifier was observed to interact with Sn+2 and promote the formation of largely oriented perovskites. Additionally, it was found that FBH results in the reduction in Sn+4 by the hydrazide group. According to the performed density functional theory calculation, the oxygen absorption barrier is increased after the FBH modification, resulting in a delay in the oxidation process. As a result of such, the interface modifier (capping layer) in the PCE increased from 8.34% to 9.47%.
Similarly, a dense layer of Al2O3 as a buffer layer separating perovskites and HTL can prevent degradation from moisture [117][20]. Cetyltrimethylammoniu bromide (CTAB) doped zirconium oxide (ZrOx) can also act in a similar manner [118][21]. In general, the switch from Pb to Sn affects the morphology severely due to the higher Lewis acidity of Sn+2 compared to Pb+2 [50][22]. Therefore, one of the major goals when making Sn films is to achieve compact and pinhole-free thin films.

3. Cation Engineering

Cations play a major role in Sn halide perovskites thin films in regard to lattice strain engineering. Nishimura et al. [119][23] investigated the relationship between lattice strain in tin-based perovskite films and TPSCs efficiency. They prepared tin-based Qx(FA0.75MA0.25)1−xSnI3 perovskites, where Q is various cations with different ionic radii such as Na+, K+, Cs+, BA+, and ethylammonium (EA+). The link between actual measured lattice strain and solar performance was explored. As the tolerance factor approached unity, the lattice strain decreased (measured by the Williamson hall plot of XRD data). As the lattice strain decreased, the performance of the Sn perovskites was enhanced. EA0.1(FA0.75MA0.25)0.9SnI3 with the lowest lattice strain yielded the best performance, because carrier mobility increased as lattice strain decreased. These lattice strains would disrupt carrier mobility and reduce solar cell performance [119][23]. The lowest lattice strains were found for Cs-0.1 and EA-0.1 and provided the highest mobility of about 43 cm2 V−1·s−1; however, in the case of Na-0.1, the lattice strain was found to be higher and therefore the mobility was down to 4.6 cm2 V−1·s−1.
Sun et al. [120][24] added a bi-linkable reductive cation (i.e., formamide (FM)), into FASnI3 to function as molecular glue for improving the stability and performance of TPSCs by the formyl group (–CHO) and amine group (−NH2). They revealed that the NH2 and C=O groups in FM are capable of interacting with FA+ and Sn+2 through hydrogen bonds and Lewis acid–base coordination, respectively. This resulted in a greater grain size, preferred orientation, lower defect density, and better film stability. The TPSC device based on 10% of FMI resulted in a 40% increased PCE from 5.51% to 7.71% with notable enhanced stability, retaining its initial PCE after one year in N2 without encapsulation.
Jokar et al. [17][25] used guanidinium cations (GA+) as an additive with at least 1% of ethylenediammonium diiodide (EDAI2) to form a FASnI3 films, and this resulted in the remarkably improved performance of TPSCs. A high PCE of 8.5% was achieved and increased to 9.6% after 2000 h of storage in a glove box. Additionally, the resulting perovskite operated for almost an hour under continuous illumination and for six days in air without encapsulation [17][25].

4. Solvent Engineering

Solvents and secondary solvents can play a major role in the formation of pinholes in thin films, especially thin films that contain organic materials [121][26]. One common way to produce a compact Sn film is by different solvents, such as dimethylformamide (DMF) or dimethyl sulfoxide (DMSO) [122,123][27][28]. Post-treatment with antisolvents also plays a crucial role in the quality of tin-based perovskite films [123,124][28][29].
It was reported that when perovskite films are formed without any anti-solvent dripping, the precursor is far from supersaturated until the solvent totally evaporates and, as a result, the nucleation site density is rather low, resulting in a flower-like film with limited surface coverage [123][28]. Therefore, different antisolvents (diethyl ether (DE), toluene (TL), and chlorobenzene (ClB)) were tested. The size of pinholes in the FA0.75MA0.25SnI3 films dripped by DE is less than that of pinholes in the film dripped by TL, but the quantity of pinholes is greater. In the case of ClB, the film has a uniform surface with full coverage and clear grain features. One reason for this could be related to its high boiling point of 131 °C, which has a slower evaporation rate, which extends the crystal development period during the thermal annealing process.
Hao et al. [42][4] investigated the DMSO function as a the Lewis base solvent to adjust the crystallization rate of MASnI3 perovskite by Lewis acid–base interaction. When DMSO molecules react with Lewis acid SnI2, they form the SnI2-3DMSO intermediate adduct, which effectively slows down the interaction between MAI and SnI2, resulting in an enhanced MASnI3 film. Similarly, the generation and orientation of FASnI3 perovskites was controlled when poly-ethylene-co-vinyl acetate (PEVA) was introduced into the anti-solvent [125][30]. At the grain boundaries, the C=O groups of PEVA molecules cause a complexation between Lewis acid–base interaction and Sn+2. This results in larger grains and lowered surface defects of FASnI3, leading to enhanced devices’ performance.

5. Low-Dimensional Perovskites

In fact, using different solvents incorporated with different additives as well as cations with different radii often has a direct influence on the dimensionality of the perovskite films, which is on its own is a major research and development direction. Lower dimension perovskites seem to be more stable than three-dimensional ones, so these are expected to improve tin-based perovskites’ stability [126][31]. The three-dimensional structure of perovskites could be decreased to two- or one-dimensional by substituting the bulky organic ammonium ions at the A-site in the perovskite lattice or by inserting 2D materials in the precursor solution [127,128][32][33]. 2D perovskites seems to have exceptional optoelectronic properties and therefore may make them excellent photovoltaic materials [129][34]. 2D perovskite reduces moisture as well as oxygen from going inside the film [130,131][35][36]. It also can reduce defects, resulting in a low amount unwanted self-doping [132][37]. Many researchers are currently investigating 2D TPSCs to increase their stability based on the benefits of lower dimension perovskites.
Similarly, low-dimensional Sn perovskites have become a topic of interest in TPSCs due to their ability to improve device performance and stability. In 2017, Liao et al. [133][38] incorporated phenylethylammonium (PEA) into FASnI3 perovskites and they achieved perpendicularly oriented, low-dimensional Sn perovskite films with remarkably enhanced stability and a PCE of 5.9%. In 2020, a report by Liang et al. [134][39] utilizing indene-C60 bisadduct (ICBA) as an ETM found that their Sn-based perovskite (PEAx FA1−xSnI3) with PEA incorporation formed a low-dimensional perovskite with reduced defect concentrations, which resulted in a high VOC of 0.94, a record PCE of 12.4%, and better stability (shelf stability of 3800 h).

6. Variety of Very Recent Perovskite Additives, Surface/interface Modifiers in TPSCs with Noticeable Performance

There are many additives that were reported in recent years to enhance the performance of TPSCs [55,72,135,136,137][40][41][42][43][44]. However, here (Table 1) wthe researchers summarize most of the very recent and noticeable additives and correlated outstanding device performance of lead-free TPSCs that were reported during the last two years. Table 2 provides a list of the most recent and highly performing surface/interface modifiers that were applied in lead-free TPSCs. Table 3 provides a list of most recent highly performing mixed Pb-Sn perovskites with Pb ≤ 50% and it includes devices with both perovskite additives and surface/interface modifiers. The table also provides structure and reported stability.
Table 1.
Best performing Pb-free TPSCs with perovskite additives reported in 2021 and 2022.
Structure Additive PCE (%) Eg (eV) Stability (Period, Conditions, Percentage from Original Efficiency)
ITO/PEDOT a/FA0.92PEA0.08SnI3/PCBM/Al /CMACl 7.1 601.42 /BCP/Cu TSC b on SnI242 days, encapsulated, 100+%

6 h, air, 60%		 [138][45]
8.2 N.A. 21 days, 1 sun, encapsulated, 71% [155][63] FTO/c-TiO2/mp-TiO2/CsSnI3/P3HT/Au * MBAA b
ITO/PTAA/FASnI7.5 3/C601.3 /BCP/Ag PEAI c on PTAA60 days, nitrogen, 60% 8.3

5 days, air, 76.5%

5 days, 1 sun, 58.4%		 [139][46]
1.4 83 days, nitrogen, 87% [56][64] ITO/PEDOT/FASnI3/C60/BCP/Ag ** FM+ t 7.7% 1.4 367 days, nitrogen, 100%
FTO/PEDOT/EDA0.01(GA0.06(FA0.8Cs0.2)0.94)0.98SnI2Br/C60/BCP/Ag[120][24]
FTO/SnO2/Al2O3-Gr c/FA0.8MA0.2SnI3/spiro d/Au * rGO e 7.7 1.27 30 days air, 42%

30 days, 85%, dry argon		 [140][47]
ITO/PEDOT/FA0.75MA0.10SnI2Br/PCBM/BCP/Ag PEA+ f 8.0 1.66 63 days, nitrogen, 100%

13 days, air, 100%		 [141][48]
ITO/PEDOT//PCBM/PCB/Ag F-PDI s 9.5 1.42 125 days, 1 sun, nitrogen, 80% [142][49]
2PACzd on PEDOT 8.7 1.62 70 days, nitrogen, 75% [156][65]
FTO/bl-TiO2/mp-TiO2/Cs0.1FA0.9SnI3/PTAA/Au * ThMAI e on PVSK 9.1 1.45 35 days, nitrogen, 92%, 6 days, air, 62% [157][66]
ITO/NiOx/FASnI3/PCBM/BCP/Ag FAAc f on PVSK 9.1 N.A. 55 days, nitrogen, 80% [158][67]
ITO/PEDOT/FA0.75MA0.25SnI2.75Br0.25/PCBM/BCP/Ag CF3PEAI g on pvsk 10.4 1.45 52 days, nitrogen, 80%, 4 days, air, 80% [159][68] ITO/PEDOT/MASnI3/PCBM/BCP/Ag EABr g 9.6
ITO/PEDOT/FA0.98EDA0.01SnI1.3 330 days, nitrogen, 93% /C60/Ag[143 SA h + PEDOT on PEDOT] 10.5 1.33[50]
83 days, nitrogen, 95% [160][69] FTO/PEDOT/FASnI3/C60/BCP/Ag FAAc h 10.0 NA 67 days, 1 sun, nitrogen, 82%
FTO/PEDOT/FA0.75MA0.25SnBrI2/ICBA/Bphene [144][51]
i/Ag ** KSCN j on PEDOT 11.2 1.63 42 days, nitrogen, 80% [161][70] PET/ITO/NiOx/FASnI3/4AMPI2 i/PCBM/BCP/Ag *** Ge/GeO2 10.4 1.38 29 days, 1 sun, nitrogen, MPP, 80%

2500 bending cycles, R = 5 mm, 80%
FTO/PEDOT/FASnI3/C60/BCP/Ag vapor of EDA k on PVSK.[145] 11.3[52]
1.42 40 days, nitrogen, 85% [162][71] ITO/PEDOT/FASnI3/C60/BCP/Ag **
ITO/PEDOT/FASnI3/CDipI j and NaBH4 k 10.6 601.38 54 days, nitrogen, MPP, 96% /BCP/Ag *** PAI l on PVSK 12.1[146][53]
1.4 ITO/PEDOT/FASnI3/PCBM/BCP/Ag EABr g 10.8 1.48 84 days, nitrogen, 82% [147][54]
ITO/PEDOT/FASnI3/PAI l/C60/BCP/Ag PEA+ f 12.1 1.4 21 days, 1 sun, MPP, encapsulated, 94% [148][55]
ITO/PEDOT/MASnI3/ICBA/BCP/Ag CsPbI3 QDs m 12.5 1.3 40 days, nitrogen, 96%

23 days, 1 sun, 62%		 [149][56]
ITO/PEDOT/FASnI3/ICBA/BCP/Ag CsPbI3 QDs 13.0 1.4 40 days, nitrogen, 83%

23 days 1 sun, 64%		 [149][56]
ITO/PEDOT/FASnI3+PHCl-Br/C60/BCP/Ag PhNHNH3+ and Ph-Cl− Br− n 13.4 1.4 14 days, 1 sun, 82%

200 days, nitrogen, 91%.		 [69][57]
ITO/PEDOT/FASnI3/ICBA/BCP/Ag 4A3HA o 13.4 1.4 83 days, nitrogen, 98%

42 days, at 82 °C, 80%		 [150][58]
ITO/PEDOT/PEAFASn(IBr)3/ICBA/BCP/Ag GAA p 13.7 NA 50 days, nitrogen, 93% [151][59]
ITO/PEDOT/FASnI3/BCP-ICBA/Ag 3T q 14.0 1.4 30 days, nitrogen, 100%

9 h, air, 85%		 [152][60]
ITO/PEDOT/FASnI3/ICBA/BCP/Ag **** PEA f Br 14.6 NA 100 days, nitrogen, 96% [153][61]
ITO/PEDOT/FASnI3/ICBA/BCP/Al FPEABr r 14.8 1.43 19 days, nitrogen, 80% [154][62]
a PEDOT:PSS (PEDOT), b N,N′-methylenebis(acrylamide), c Graphene (Gr), d spiro-OMeTAD, e reduced graphene oxide (rGO), f phenylethylammonium (PEA+), g ethylammonium bromide (EABr), h formamidine acetate (FAAc), i 4-(aminomethyl) piperidinium diiodide (4AMPI2), j Dipropylammonium iodide (DipI), k sodium borohydride (NaBH4), l n-propylammonium iodide (PAI), m quantum dots(QDs), n phenylhydrazine (PhNHNH3+) and phenylhalides (Cl− and Br−) (Ph-Cl−Br−), o 4-amino-3-hydroxybenzoic acid (4A3HA), p 2-Guanidinoacetic acid (GAA), q trimethylthiourea (3T), r 4-fluoro-phenethylammonium bromide (FPEABr), s fluorinated-perylene diimide (F-PDI), t formamide (FM), * n-i-p structure, ** one of the best stability records, *** flexible record and with NiOx HTL, **** with SnI2-DMSO colloidal complex.
Table 2. Surface and Pb-free. Best-performing Pb-free TPSCs with perovskite surface/interface modifiers reported in 2021 and 2022.
Structure Treatment PCE (%) Eg (eV) Stability (Period, Conditions, Percentage from Original Efficiency)  
ITO/PEDOT a/CsSnI3
21 days, 1 sun, MPP, encapsulated, 94%
[
148
]
[
55
]
ITO/PEDOT/FASnI3/C60/BCP/Ag PMMA m on PVSK 13.8 1.41 42 days, 1 sun, encapsulated, MPP, 94% [163][72]
ITO/PEDOT/FAMASnI3/C60/BCP/Ag FACl on PVSK 14.7 1.42 42 days, nitrogen, 92% [164][73]
a PEDOT:PSS (PEDOT), b thiosemicarbazide (TSC), c phenylethylammonium iodide (PEAI), d carbazole with phosphonic acid (2PACz), e 2-thiophenemethylammonium iodide (ThMAI), f formamidine acetate (FAAc), g 3-(trifluoromethyl) phenethylamine hydroiodide (CF3PEAI), h zwitterion, sulfamic acid (SA), i bathophenanthroline (Bphene), j potassium thiocyanate (KSCN), k ethane-1,2-diamine (EDA), l n-propylammonium iodide (PAI), m poly-methyl methacrylate (PMMA). * n-i-p structure, ** Indoor PCE-record of 17.6% under 1062 lx, *** cold precursor solution (0 °C).
Table 3. Additives/surface and Pb ≤ 50%. Best-performing TPSCs with lead content ≤ 50% with perovskite surface/interface modifiers or perovskites additive reported in 2021 and 2022.
Structure Additive/Treatment PCE (%) Eg (eV) Stability (Period, Conditions, Percentage from Original Efficiency)  
ITO/PEDOT a/FASn0.5Pb0.5I3/C60/BCP/Ag K-SCN b additive 14.5 1.25 5 days, air, 55% [165][74]
ITO/PEDOT/FA0.8MA0.15Cs0.05Pb0.5Sn0.5I3/C60/BCP/Ag PEAI c additive 17.3 1.25 33 h, air, 85%

45 days, nitrogen, 87%		 [166][75]
ITO/FA0.85Cs0.15Sn0.5Pb0.5I3/PCBM/PCB/Cu * FSA d additive and PEAI c in toluene on PVSK 17.4 1.27 20 days, air, 81% [167][76]
ITO/PEDOT/FA0. 5MA0.5Pb0.5Sn0.5I3/PCBM/C60/BCP/Ag IMBF4 e additive 19.1 1.25 42 days, nitrogen, 90%

2 days, 1 sun, 80%		 [168][77]
ITO/PEDOT/FA0.83Cs0.17Pb0.5Sn0.5I3/C60/BCP/Ag PEAI c on PVSK 19.1 NA 4 days, nitrogen, 1 sun, MPP 82% [169][78]
ITO/NiOx/FA0.5MA0.5Sn0.5Pb0.5I3/PC61BM/BCP/Ag PFN f on NiOx 19.8 1.26 20 days, air, 68% [170][79]
ITO/PEDOT/FA0.7MA0.3Pb0.5Sn0.5I3/PCBM/BCP/Cu. CA g additive 19.9 1.26 21 days, nitrogen, 90% [171][80]
ITO/Cs0.05MA0.45FA0.5Pb0.5Sn0.5I3/PCBM/C60/BCP/Ag * Cu-SCN b and GlyHCl h on ITO 20.1 1.21 42 days, nitrogen, 90%

4 days, 1 sun, MPP, 72%		 [172][81]
ITO/PEDOT/FA0.7MA0.3Pb0.5Sn0.5I3/PCBM/BCP/Ag [PNA]BF4 i on PEDOT 20.1 NA 10 days, nitrogen, 85 °C, 80%

50 days, nitrogen, 90.8%		 [173][82]
ITO/PEDOT/FA0.7MA0.3Pb0.5Sn0.5I3/C60/BCP/Ag PhDMADI j additive 20.5 1.25 29 days, nitrogen, 95% [174][83]
ITO/PEDOT/MA0.3FA0.7Pb0.5Sn0.5I3/PCBM/BCP/Ag GUA k additive and HAI l on PVSK 20.5 1.27 6 days nitrogen, 1 sun, 60% [175][84]
FTO/PEDOT/Cs0.025FA0.475MA0.5Sn0.5Pb0.5I2.925Br0.075/PCBM/C60/BCP/Ag RbI additive 21.0 1.28 6 days, nitrogen, at 85 °C, 75%

30 days, nitrogen, 99%		 [176][85]
ITO/PEDOT/FA0.5MA0.5Pb0.5Sn0.5I3/C60/BCP/Ag HZBA m additive 21.1 1.26 8 days, nitrogen, 90% [177][86]
ITO/PEDOT/Cs0.2FA0.8Pb0.5Sn0.5I3/C60/BCP/Cu BaI2 additive 21.2 1.21 15 days, encapsulated, 1 sun, MPP, 95% [178][87]
FTO/PEDOT/FA0.6MA0.4Sn0.6Pb0.4I3/C60/BCP/Ag N,Cl-GQDs o at PEDOT 21.5 1.25 42 days, nitrogen, 90% [179][88]
ITO/PEDOT/Cs0.05FA0.7MA0.25Sn0.5Pb0.5I3/C60/BCP/Ag BBMS n + SnF2 22.0 1.22 111 days, nitrogen, 60 °C, 98 % [180][89]
ITO/PEDOT/FA0.6MA0.4Sn0.6Pb0.4I3/C60/BCP/Ag. PEAI c and guanidinium-SCN b 22.1 1.25 76 days, nitrogen, MPP, 82% [181][90]
ITO/CzAnp/PMMA/FA0.8Cs0.2Sn0.5Pb0.5I3/PCBM/C60/BCP/Cu CzAn p HTM and BHC q on PVSK 22.6 1.22 7 days, encapsulated, MPP, 1 sun, 90%

42 days, encapsulated, 96%		 [182][91]
FTO/Cs0.025FA0.475MA0.5Sn0.5Pb0.5I2.925Br0.075/EDA r/PCBM/C60/BCP/Ag * 2PACz s and MPA t at FTO 23.3 1.25 42 days, nitrogen, 1 sun, 100% [183][92]
FTO/PEDOT/Cs0.1FA0.6MA0.3Sn0.5Pb0.5I3/C60/BCP/Ag EDAI2 u on PVSK and GlyHCl v at PEDOT 23.6 1.24 8 days, nitrogen, 1 sun, MPP, 80% [184][93]
a PEDOT:PSS (PEDOT), b thiocyanate (SCN), c 2-phenylethylazanium iodide (PEAI), d formamidine sulfinic acid (FSA) additive, e ionic imidazolium tetrafluoroborate (IMBF4), f poly[(9,9-bis(30-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyfluorene)] (PFN), g caffeic acid (CA), h glycine hydrochloride (GlyHCl), i iso-pentylammonium tetrafluoroborate salt ([PNA]BF4), j p-phenyl dimethylammonium iodide (PhDMADI), k β-guanidinopropionic acid (GUA), l hydrazinium iodide (HAI), m 4-hydrazinobenzoic acid (HZBA), n 1-bromo-4-(methylsulfinyl) benzene (BBMS), o graphene quantum dots (GQDs), p poly[(phenyl)imino[9-(2-ethylhexyl)carbazole]-2,7-diyl] (CzAn), q benzylhydrazine hydrochloride (BHC), r Ethylenediamine, s 2-(9H-carbazol-9-yl) ethyl] phosphonic acid (2PACz), t methyl phosphonic acid (MPA), u ethylenediammonium diiodide (EDAI2), v glycine hydrochloride (GlyHCl), * HTL-free.
It is noteworthy to mention that the reasons behind the enhancement of the performance of the devices listed in the tables are often related to the same reasons. Here, wthe researchers briefly list the reasons behind the enhancement in general, which is important for further future consideration and development to achieve even higher performance: (i) oxidation, (ii) reduced defects, (iii) controlled crystallization, (iv) morphology (compactness and pinholes, strain relaxation), (v) charge diffusion and extraction (mobility, carriers density, energy levels, recombination), (vi) built-in electric field (gradient vertical perovskite growth), (vii) better choice of cations (reduced or eliminated MA+) (iix) hydrophobicity, and (ix) passivation of the acidic and hygroscopic surface of the commonly used PEDOT:PSS HTL (or alternative or HTL or SAMs).

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