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STAR Protoc
STAR Protoc
STAR Protocols
2666-1667
Elsevier

S2666-1667(24)00430-1
10.1016/j.xpro.2024.103265
103265
Protocol
Protocol for fabricating long-lasting passivated perovskite solar cells
Wang Sisi wangsisi@westlake.edu.cn
123∗
Sun Jingyi 2
Xue Jingjing 2
Wang Rui wangrui@westlake.edu.cn
14∗∗
1 School of Engineering, Westlake University and Institute of Advanced Technology, Westlake Institute for Advanced Study, Hangzhou 310024, China
2 State Key Laboratory of Silicon and Advanced Semiconductor Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou, China
∗ Corresponding author wangsisi@westlake.edu.cn
∗∗ Corresponding author wangrui@westlake.edu.cn
3 Technical contact

4 Lead contact

14 8 2024
20 9 2024
14 8 2024
5 3 103265© 2024 The Author(s)
2024
https://creativecommons.org/licenses/by-nc/4.0/ This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).
Summary

Preparation of perovskite solar cells (PSCs) with long-lasting passivation effectiveness is challenging. Here, we present a protocol for fabricating efficient and stable passivated perovskite solar cells. We describe steps for preparing the electron transporting layer (ETL) via chemical bath deposition and perovskite film. We then detail procedures for passivating the surface defects with excess terpyridine ligands and stability characterization. This protocol features a passivator-terpyridine whose passivation effect is independent of concentration, which greatly improves the durability of the passivation.

For complete details on the use and execution of this protocol, please refer to Wang et al.1

Graphical abstract

Highlights

• Protocol to fabricate efficient and stable PSCs

• Steps for fabricating ETLs of SnO2 via chemical bath deposition

• Instructions for fabricating and passivating perovskite films

• Details on the characterization of the long-term stability of the PSCs

Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.

Preparation of perovskite solar cells (PSCs) with long-lasting passivation effectiveness is challenging. Here, we present a protocol for fabricating efficient and stable passivated perovskite solar cells. We describe steps for preparing the electron transporting layer (ETL) via chemical bath deposition and perovskite film. We then detail procedures for passivating the surface defects with excess terpyridine ligands and stability characterization. This protocol features a passivator-terpyridine whose passivation effect is independent of concentration, which greatly improves the durability of the passivation.

Subject areas

Physics
Energy
Chemistry
Material sciences
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pmcBefore you begin

Scope and structure

This protocol is about how to fabricate n-i-p structured terpyridine-passivated PSCs, whose sandwich structure consisting of an electron transport layer (ETL), perovskite light absorbing layer, and a hole transport layer (HTL). This protocol below describes the specific steps to prepare electron transporting layer (ETL) via chemical bath deposition, prepare perovskite film via two-step method, passivate the surface defects with excess terpyridine ligands, and stability characterization. This protocol may also be suitable for fabricating PSCs with other perovskite absorbers (e.g., bromide and iodide mixed perovskites) or with other different self-aggregated passivator agents. Protocol steps in this section have been partially modified from Khan et al.,2 including operation of sensitive drug storage, glove box maintenance and preparation of accessories for evaporation equipment.1. It is recommended to use thioglycolic acid (TGA) that is less than 1 year old and store it in the refrigerator received from manufacturer, as TAG can easily hydrolyze and deteriorate.

2. Prepare the patterned Fluorine doped tin oxide (FTO) substrates with 7–15 Ω/sq. The substrates can be patterned by laser or chemical etching. We preferred customizing laser-etched pre-patterned substrates from supplier, as this reduces errors from the substrate and improves repeatability.

3. Perform a purge operation before using the glove box and check the oxygen and moisture levels in the glove box, which should be approximately or less than 1 ppm for H2O and 10 ppm for O2.

4. The evaporation sources in the thermal evaporator should each be equipped with a protective cover to avoid cross-contamination. Clean the evaporation chamber regularly to remove metal scale deposited in the inner chamber.

5. Prepare clean glass container (e.g., preparation Thin-layer chromatography (TLC) tank as shown in Figure 1A) for chemical bath deposition (CBD) of SnO2 layers.Figure 1 Materials used in the device fabrication

(A) Photographs of the preparation TLC tank, (B) substrate holder with metal grid mask, (C) pre-taped FTO is fixed to the glass substrate, (D) perovskite film (marked part should be removed), and (E) perovskite solar cell, which contains 5 sub-cells on each piece. The A position is directly contact with the FTO bottom electrode.

6. Prepare substrate holder with metal grid mask as shown in Figure 1B for depositing silver electrodes on top of HTL layer.

7. Confirm that the thermal admittance spectroscopy measurement is working by measuring the C-V and C-f curves of reference cell, make sure the devices are working properly and measuring the correct values.

8. Replace a new white LED light to ensure long-lasting illumination during the light stability test.

Key resources table

REAGENT or RESOURCE	SOURCE	IDENTIFIER	
Chemicals, peptides, and recombinant proteins	
	
Dimethylsulfoxide (DMSO, anhydrous, 99.9%)	Sigma-Aldrich	Cas# 67-68-5	
Dimethyl formamide (DMF, anhydrous, > 99.8%)	Sigma-Aldrich	Cas#68-12-2	
Isopropyl alcohol (IPA, anhydrous, 99.5%)	Sigma-Aldrich	Cas#67-63-0	
Chlorobenzene (CB, anhydrous, 99.5%)	Sigma-Aldrich	Cas#108-90-7	
Acetonitrile (ACN, anhydrous, 99.9%)	Sigma-Aldrich	Cas#75-05-8	
Thioglycolic Acid (TGA, 99%)	Sigma-Aldrich	Cas#68-11-1	
Tin(II) chloride dihydrate (SnCl2.2H2O, 99.99%)	Sigma-Aldrich	Cas#10025-69-1	
Urea (99%)	Sigma-Aldrich	Cas#57-13-6	
Formamidinium iodide (FAI, 99.9%)	Greatcell Solar	Cas#879643-71-7	
Lead iodide (PbI2, ultra-dry, beads, 99.999%)	Alfa Asear	Cas#10101-63-0	
Methylammonium Chloride (MACl, 99.99%)	Greatcell Solar	Cas# 593-51-1	
Phenethylammonium iodide (PEAI, 98%)	Xi’an Polymer Light
Technology. Corp.	Cas#151059-43-7	
Molybdenum oxide (MoO3, 99.5%)	Alfa Aesar	Cas#1313-27-5	
Silver wire (99.999%)	Alfa Aesar	Cas#7440-22-4	
2,2′,7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD, 99.9%)	Xi’an Polymer Light
Technology. Corp.	Cas#207739-72-8	
Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, 99.95%)	Sigma-Aldrich	Cas#90076-65-6	
4-tert-butylpyridine (tBP, 98%)	Sigma-Aldrich	Cas#3978-81-2	
2,2′:6′,2″-Terpyridine (terpyridine, 98%)	LaaJoo A Sinocompound Corp.	Cas#1148-79-4	
	
Other	
	
Sun simulator	Enlitech Instruments, AAA class	N/A	
PTFE hydrophilic membrane filters, 0.45 mm, 90 mm	VWR	Cat#28145-493	
Glove box	MBRAUN	MB-Unilab Pro SP (2000/780)	
Thermal evaporator	Moorfield	MiniLab 060	
Spin coater	Laurell Technologies	Model WS-650Mz-23NPPB	
Micro weighing balance	Sartorius	ENTRIS124I-1S	
UV ozone cleaner	Ossila Limited	L2002A1	
Indium F-doped tin oxide (FTO)-coated glass slides	Liaoning Youxuan New Energy Technology Co., Ltd	1.5 cm by 1.5 cm size; 2.2 mm thickness	
Stability test system	Home-made	N/A	
Hot plate	Heidolph	Hei-PLATE Mix 'n' Heat Core＋	
Thermal admittance spectroscopy measurement	Lake Shore Cryotronics	N/A	
X-ray diffraction (XRD) measurement	Bruker	D8 Advance	

Materials and equipment

TGA is stored in a fridge at ∼8°C. Urea is stored in a dry cabinet with relative humidity (RH) below 20%. SnCl2.2H2O, FAI, PbI2, MACl, terpyridine and solvents should be stored in N2-filled glovebox. The recipe of precursor solution for SnO2-ETL is shown in Table 1, the recipe of precursor solution for perovskite layer is shown in Table 2, and the recipe of precursor solution for doped HTL is shown in Table 3. The PSC test system is built by Enlitech Instruments and placed in an N2-filled glovebox (see schematic illustration in Figure 5), including a Keithley 2400 sourcemeter, a Xenon lamp solar simulator, and IVS-KA6000 PV Test IV software. The power of the light was calibrated to 100 mW/ cm-2 by a silicon reference cell (with a KG1 filter). The J-V characteristics of photovoltaic cells were obtained using a Keithley 2400 source measure unit under a simulated AM 1.5G spectrum. Typically, the devices were measured in reverse scan mode (1.20 V → 0 V, step 0.02 V). All the devices were measured without pre-conditioning such as light-soaking and a bias voltage applied.Table 1 Precursor solutions for CBD-SnO2 ETL

Reagent	Final concentration	Amount	
SnCl2.2H2O in H2O	2.75 mg/mL	80 mL	
Urea in H2O	12.5 mg/mL	80 mL	
HCl	N/A	1 mL	
TGA	N/A	20 μL	
Note that store at 4°C for up to a week.

Table 2 Precursor solutions for perovskite layer

Reagent	Final concentration	Amount	
PbI2 in DMF/DMSO(940/60)	668.5 mg/mL	1 mL	
CsI in DMF/DMSO(940/60)	18.78 mg/mL	1 mL	
MACl in IPA	13.4 mg/mL	1 mL	
FAI in IPA	82.8 mg/mL	1 mL	
Note that store at 25°C for less than a week.

Table 3 Precursor solutions for doped spiro-OMeTAD HTL

Reagent	Final concentration	Amount	
LiTFSI in ACN	520 mg/mL	20 μL	
tBP	N/A	40 μL	
Spiro-OMeTAD in CB	72.6 mg/mL	1 mL	
Note that store at 25°C for less than 3 days.

The shelf life of TGA is around a year at 8°C. A longer storing time may result in oxidization and deterioration. SnCl2.2H2O should be stored in an N2-filled glovebox (O2 < 1 ppm; H2O < 1 ppm). FTO glass is cleaned by sonicating in detergent solution, deionized water, acetone, and IPA for no more than 20 min each. We suggest using freshly washed FTO glass.CRITICAL: Hydrochloric acid (HCl) is corrosive and TGA is toxic. When working with these chemicals in a well-ventilated fume hood, wear appropriate personal protective equipment (PPE) products (eye protection, face shield, and gloves).

Alternatives: General chemicals used in this program (e.g., CB, IPA, DMSO, and DMF) can be replaced by other brands. Instruments used in this program can also be replaced with instruments with similar capabilities. For example, O3 plasma can also be used to clean FTO glass instead of UV ozone.

Step-by-step method details

Since the basic procedures for optoelectronic device preparation have been matured and standardized, such as the cleaning of the conductive glass and electrode evaporation, protocol steps in this section are partially modified from Zou et al.3 and Khan et al.2

ETL fabrication

Timing: 10–15 h

Timing: 1.5–2.5 h (for step 1)

Timing: 7–10 h (for step 2)

Timing: 1.5–2.5 h (for step 3)

The fabrication of ETL here includes cleaning FTO substrate via sonication, depositing SnO2 on FTO substrate via chemical bath method, and post-treatment on the as-prepared SnO2/FTO substrate. The following steps describe detailed processes of synthesizing SnO2 micelle and consequent post-treatment steps, as the schematic shown in Figure 2.1. Substrate cleaning.a. Mark the corners on the back of the FTO substrate (2 cm∗2 cm) for identification and place in the holder for further cleaning.

b. Ultrasonicate the substrates in 1%∼5% Hellmanex solution (by diluting in deionized water) for 10–20 min at 30°C, depending on the sonication frequency.

c. Wash the substrates three times with deionized water for 10 min each time.

d. Ultrasonicate the substrates in acetone for 20 min at 30°C.

e. Ultrasonicate the substrates in isopropanol for 20 min at 30°C.CRITICAL: Prolonged operation of the ultrasonic cleaner can cause the water temperature to rise rapidly. Regular water changes or ice are recommended.

f. Dry the substrate quickly with a dry air gun.

2. Deposition of SnO2 on FTO substrate (see Figure 2A).a. Add 1000 mg urea to 80 mL H2O in a beaker.

b. Stir the solution until completely dissolved.

c. Add 1 mL of HCl solution to the beaker and then stir for 2 min.

d. Dissolve 220 mg SnCl2.2H2O powder into the beaker and then stir 2 min.

e. Add 20 μL of TGA into the beaker and then stir 5 min (see Figure 2A–2).

f. Adhere the FTO glass to the coverslip with high-temperature tape arranged as in Figure 1C (see Figure 2A–1), and then transferred to the preparation TLC tank.

g. Pour the mixed solution to the tank (seeFigure 2A–3) and then put the tank in an oil bath at 90°C for 5–7 h (see Figure 2A–4).

Alternatives: The SnO2 precursor solution in this protocol can be aged in in fridge for 4 days before use, but the consequent change is that the deposition temperature is room temperature and the deposition time is 2 days, which is more time-consuming.4

Alternatives: The single SnO2 chemical bath deposition with a total time of 5–7 h in this protocol can be replaced by repeating the SnO2 chemical bath deposition twice with a total time of 2.5–3.5 h each time.5

3. Post-treatment of FTO/SnO2 substrate (see Figure 2B).a. Remove the tank from the oil bath when the chemical bath deposition solution turns murky.CRITICAL: The temperature of reaction tank is high, TGA and HCl is volatile. One should wear proper heat protective equipment products when removing the tank to a well-ventilated fume hood.

b. Transfer the FTO/SnO2 substrate to another tank filled with deionized water when they are cooled to room temperature (see Figure 2B–1).

c. Ultrasonically cleaned in water for 5 min at 30°C (see Figure 2B–2).

d. Ultrasonicate the substrates in isopropanol for 20 min at 30°C (see Figure 2B–3).

e. Dry the FTO/SnO2 substrate rapidly using dry air gun (see Figure 2B–4).

f. Put the FTO/SnO2 substrates on a 180°C hotplate for 1 h (see Figure 2B–5).

g. Store the FTO/SnO2 substrates in a dry cabinet with relative humidity (RH) below 20% after they has cooled down to room temperature.Note: The time point at which the solution turns murky is not fixed. You can determine the end point of the CBD reaction with the help of a red laser pointer to test the Tyndall effect of the solution. In general, you can stop the reaction when you can observe a clear light column.

CRITICAL: The Sn intermediate species during chemical bath deposition play a crucial part in the quality of the final SnO2 layer. For more detail, please read the work by Yoo et al.6

Alternatives: The CBD methods for preparing SnO2 layer may vary. For example, an alternative way is pre-spin-coating a layer of SnCl2.2H2O prior to CBD, which is then thermally decomposed into SnO2. In addition to that, a layer of SnCl4 could also be spin-coated on top of the CBD SnO2, which is then thermally decomposed into a layer of cl-doped SnO2.7

Figure 2 The steps of preparation of FTO/SnO2 substrate

(A) Synthesis of SnO2 layer via chemical bath deposition.

(B) Post annealing of SnO2 substrate.

Fabrication of perovskite active layer and hole selective contact

Timing: 32 h

Timing: 18 h (for step 4)

Timing: 12 h (for step 5)

Timing: 1–2 h (for step 6)

The following steps describe detailed processes of depositing light-absorbing functional layer and hole transport layer of PSCs, which is illustrated in Figure 3.4. Fabrication of perovskite film.a. Place all FTO/SnO2 glass substrates in UV-Ozone cleaner, FTO side up, and treat with UV-Ozone for 15 min before use ((Figure 2B–6)).

b. Transfer the FTO/SnO2 substrates into an N2-filled glovebox (O2 < 1 ppm; H2O < 1 ppm).CRITICAL: Use the UV-treated substrate as soon as possible. If the substrate has not been used for a long time, it is recommended to re-UV-zone it before use.

c. Prepare perovskite precursor solutions: Dissolve 668.5 mg and 18.78 mg of PbI2 and CsI in 1 mL of mixed solvents consisting of 940 μL of DMF and 60 μL of DMSO, and then stir the precursor at 22°C–25°C for 12 h. The mixed organic cation solution of FAI: MACl (82.8: 13.4 mg/mL) was dissolve in 1 mL IPA at 22°C–25°C and stir for 1 h.

d. Cast 40 μL CsI/PbI2 solution on the center of the FTO/SnO2 and spin-coat at 1500 rpm for 40 s with an acceleration of 200 rpm/s (See Figure 3A–1).

e. Dynamically cast 47 μL of the mixed organic cation solution on the wet PbI2 film without stopping.

f. Continue the spin coating at 1800 rpm for 40 s.

g. Anneal the as-prepare film at 90°C for 1 min in N2-filled glovebox.

h. Transfer the perovskite films to air.

i. Anneal the perovskite films at 150°C for 10 min in air with 30%–40% relative humidity (RH).CRITICAL: The atmosphere in the glove box is critical to the quality of the perovskite films. Perovskite precursor solutions commonly contain solvents with a high coordination affinity for PbI2, such as dimethyl sulfoxide and 1-methyl-2-pyrrolidone (NMP), vapor residues of these solvents in the glove box can affect the intermediate phase as well as the crystallization dynamics of the perovskite films during the thermal annealing process. In addition, vapor residues of chlorobenzene, a common solvent used in the preparation of perovskites, can affect the nucleation dynamics during spin-coating process. Therefore, it is strongly recommended to change the contaminated foil as often as possible during the spin-coating process (or with a purge process). Similarly, the glove box should be purged and cleaned before depositing different solutions.

CRITICAL: Temperature control of the glove box is critical for the quality and reproducibility of the perovskite films. It is recommended that the glove box be equipped with an air conditioning or condensing unit and that the temperature be maintained at 22°C–25°C.

j. Transfer perovskite films into N2-filled glovebox.

k. Deposit 30 μL terpyridine (100 mM in IPA) solution on perovskite surface with a static spin-coating process at 3,000 rpm for 30 s.

l. Let perovskite films stand overnight to allow the terpyridine to fully form spherical crystals.CRITICAL: The appearance of terpyridine film is of critical importance to the performance of the PSCs. Device performance is good only if the terpyridine forms spherical crystals on the perovskite surface. This is because high concentration of terpyridines form ordered π-π stacking, which facilitates charge transport at the interface. We show representative characteristics of the perovskite surface and corresponding devices with and without spherical crystals after deposition of 100 mM terpyridine in Figures 4A–4F. In addition, it is suggested to strictly control the purity of terpyridine raw materials and stirring time of terpyridine solution. This is because terpyridine easily forms disordered crystals on the perovskite surface in the case of containing excessive impurities. The coverage of spherical crystals on perovskite surface is poor due to the lack of nucleation sites in the case of long-term stirring.

Figure 4 Perovskites with different terpyridine morphologies and corresponding current density-voltage (J-V) curves

(A) Static spin-coating using terpyridine solution after 2 h stirring.

(B) Static spin-coating using terpyridine solution with over-night stirring.

(C) 60 s dynamic spin-coating without forming spherical crystals.

(D) Static spin-coating followed by thermal annealing at 90°C and IPA vapor treatment with forming yellow low-dimensional phase.

(E) Static spin-coating using terpyridine with impurities.

(F) Static spin-coating using terpyridine solution with excessive stirring.3. Deposition of top electrodes.

5. Deposition of HTL.a. Prepare 72.3 mg Spiro-OMeTAD in 1 mL CB with 25.5 μL t-BP, 15.5 μL Li-TFSI (520 mg/mL in ACN), and stir at room temperature for 0.5 h.CRITICAL: Spiro-OMeTAD solutions containing additives and dopants are generally stored in the N2-filled glovebox for less than 48 h does not significantly influence the results. However, it is advised to use it directly.

b. Cast 20 μL Spiro-OMeTAD solution on perovskite film to dynamically spin-coat at 3000 rpm for 30 s with acceleration.c.Store samples in a dry cabinet (30°C, RH< 20%) for 12 h.

6. Deposition of top electrodes.a. Transfer samples to the thermal evaporation chamber.CRITICAL: Depositing the electrodes only after the film has changed from its initial purple color to a golden yellow ensures that the device gets normal fill factor.

b. Scraped off the perovskite film (the area marked by the red rectangle in Figure 1D) with a razor blade to expose the ITO cathode.

c. Clean the sample with a N2 gun to remove excess dust particles.

d. Control the rotation speed of the substrate holder to 10 rpm/s during the evaporation process.

e. Pump the vacuum chamber to a pressure below 4 × 10−6 mbar.

f. Deposit 7-nm-thick MoO3 at a rate of 0.2 A°/s.

g. Deposit 120-nm-thick silver in the following way: the first 20 nm with the speed of 0.1 A°/s and then at 1.5 A°/s up to 120 nm.

h. Define the active area of PSCs as 0.1 cm2 by a shadow mask (Figure 1E).Alternatives: When the storage time of the sample in the drying cabinet accidentally exceeds 12 h, it does not matter; you can skip the thermal vaporization of molybdenum oxide and directly vaporize metal Au. Test the parameters of the device, if the FF is lower than 77%, you can continue to oxidize the device in the drying cabinet until the FF reaches 79% or more, and then transfer the device to the glovebox.

Figure 3 Steps for fabrication of PSCs

(A) Signed 1–6, deposition of perovskite layer, and hole transport layer; Signed A to B, surface passivation with terpyridine.

(B) Signed 7, deposition of MoO3 and metal electrode in a thermal evaporator with a shadow mask.

Characterization of devices

Timing: variable

Timing: 30 min to 1 h (for step 7)

Timing: 56–60 h (for step 8)

Timing: 1–2 weeks (for step 9)

Timing: variable (for step 10)

The characterization of PSCs here includes J-V curve measurement, X-ray Diffraction measurement, thermal admittance spectroscopy measurement and stability test. The following steps describe detailed processes of performing J-V scanning to evaluate power conversion efficiency (PCE) and monitor the evolution of device PCE under thermal stress or continuous illumination, performing X-ray diffraction measurement to monitor the evolution of perovskite lattice under thermal stress, and performing thermal admittance spectroscopy measurement to calculate the defect density of fresh and aged device.7. J-V measurement.

The current density characteristics of the devices was measure under AM1.5G (100 mWcm-2) illumination in an N2-filled glovebox with the help of AAA grade solar simulator (Enlitech) as shown in Figure 5. Before starting the J-V measurement, calibrate the light illumination by using standard Silicon (KG1-Si) cell. For this, the standard Si solar cell was kept at the center of the simulated xenon light source, at a similar height as of devices.a. Adhere the shadow mask to the un-encapsulated solar cells to define the active area (0.1 cm2) to reduce the influence of scattered light.

b. Measure J-V curves under reverse scan: from 1.2 V to −0.1 V, scan-rate 50 mV s−1, delay time 30 ms, and pre-sweep delay: 10 s.Note: Store freshly fabricated devices in a N2-filled glovebox for 36 h and perform J-V tests every 12 h. The champion PCE is usually achieved in the second or third test.

Figure 5 Illustrating the measurement of J-V characteristics of solar cells

8. X-ray Diffraction (XRD) measurement.a. Perform XRD measurement on freshly prepared samples.

b. Place samples on 85°C for 7 h in RH of 30%–40% to accelerate the perovskite degradation.

c. Perform XRD measurement on the first aged samples.

d. Place samples on 85°C for 13 h.

e. Perform XRD measurement on the second aged samples.

f. Place samples on 85°C for 14 h.

g. Perform XRD measurement on the third aged samples.

h. Place samples on 85°C for 22 h.

i. Perform XRD measurement on the fourth aged samples.

9. Thermal admittance spectroscopy measurement.

The trap density of states (tDOS) for device is deduced from angular frequency-dependent capacitance according to the following formulae via Cryogen-free cryogenic probe stations & 4200A-SCS (CRX-4K).NT(Eω)=−VbiqwdCdωωkBT

Eω=kBTIn(2πv0T2ω)

where Vbi is the built-in potential, v0 is the temperature-independent attempt-to-escape frequency, kB is the Boltzmann constant, W is the depletion width, q is the elementary charge, C is the capacitance, and ω is the applied angular frequency.a. Place the sample on the stage.

b. Connect the probes to the top and bottom contact and check the connectivity from a multimeter.CRITICAL: The spiro-OMeTAD layer of device samples used for TAS measurement must be well oxidized to ensure an FF value of 78% or more. Otherwise, too high a series resistance makes measurement difficult or even impossible.

CRITICAL: The probe used for the test has an impact on the measurement. It is advised to use soft probe.

c. Pump the vacuum chamber to a pressure below 5 × 10-4 mbar in 30 min.

d. Perform C-f test. Set the d.c. bias(V) at 0 V, the amplitude of the a.c. bias (δV) at 20 mV, and the scanning range of the a.c. frequency (f) at 0.02–2000 kHz.

e. Perform c-v test. Set the a.c. frequency (f) at 1 kHz, the amplitude of the a.c. bias (δV) at 20 mV, and the scanning range of the d.c. bias(V) at 0–1.2 V.

f. Store the PSCs in a dry cabinet (20°C–25°C, RH< 20%) for 2 weeks.

g. Perform C-V and C-F measurements again on the aged PSCs.Note: More information about the analytical solutions to estimate the characteristic frequencies of trap peak in the differential capacitance spectrum and the experimental details of TAS measurement of the perovskite solar device can be found in the following literature: Wang et al.,8 Ni et al.,9 and Ni et al.10

10. Device stability test.a. Perform J-V measurements on freshly fabricated PSCs.

b. Place half of samples on 65°C hot plate in a N2-filled glove and expose the remaining half to continuous illumination in another N2-filled glove (Figure 5).

c. Perform and record J-V data at intervals.

CRITICAL: When storing, ensure that the electrode is facing upwards to prevent friction damage to the electrode.

Note: Light soaking tests promote ion and defect migration in PSCs as well as phase segregation the perovskite photoactive layer. Dark storage studies provide information on the tolerance of the solar cells to oxygen, moisture, other aggressive atmospheric components naturally present in air, and elevated temperatures. We conducted these stability tests according to Organic Photovoltaic Stability (ISOS) protocols.11

Expected outcomes

The important outcomes of the present protocols are illustrated below:

Perovskite films passivated by high concentrations of terpyridine show a surface covered with spherical crystals. The appearance of spherical crystals indicates that terpyridine molecules form an ordered π-π stacking. The characteristic peaks of the PbI2-adducts are not observed in the XRD pattern, which suggests terpyridine does not disrupt the perovskite lattice. See detailed surface structure in Figure 6.Figure 6 Surface structure

(A) Photographs of reference and 100-mM-terpyridine passivated perovskite films.

(B) XRD patterns of fresh reference and fresh 100-mM-terpyridine passivated perovskite films.

(C) XRD evolution of reference perovskite films during aging.

(D) XRD evolution of 100-mM-terpyridine passivated perovskite films during aging.

Trap density states of 100-mM terpyridine treated devices decrease after 148 h aging test. In contrast, the defect state density of the reference device increased under the same aging conditions.

Under a constant illumination or heat, devices with 100-mM-terpyridine treatment show superior stability relative to the reference device. See detailed device performance in Figure 7.Figure 7 Device performance

(A) Trap density of reference devices before and after 148 h aging test. Reproduced with permission from (Wang et al., 2024).

(B) Trap density of 100-mM-terpyridine treated devices before and after 148 h aging test. Reproduced with permission from (Wang et al., 2024).

(C) J-V curve of reference and 100-mM-terpyridine passivated PSCs.

(D) Device light stability tests of reference and 100-mM-terpyridine passivated PSCs. Reproduced with permission from (Wang et al., 2024).

(E) Device thermal stability tests of reference and 100-mM-terpyridine passivated PSCs. Reproduced with permission from (Wang et al., 2024).

Limitations

In principle, highly efficient and stable PSCs with n-i-p configurations can be fabricated using this protocol, in which the recipe of the perovskite can be adjusted. It should be noted that this recipe and spin-coating parameters for the perovskite functional layer are only applicable in N2 atmosphere. In addition, care should be taken to avoid the use of Lewis acid-doped HTL materials in the preparation of hole transport layers (HTLs), as the passivator can strongly interact with the dopant of the HTL, leading to doping failure.

Troubleshooting

Problem 1

When heated for more than 6 h, the chemical bath deposition solution remained undisturbed, and no Tyndall effect was observed.

Potential solution

Replace distilled water or reduce the amount of hydrochloric acid. When the chlorine ions in the water exceed a certain value, the solution does not become murky.

Problem 2

The as-prepare film (step 4d) annealed at 90°C for 1 min in N2-filled glovebox did not turn completely black, some orange-yellow phase is present.

Potential solution

Reduce the concentration of FAI: MACl solution or increase its spin-coating speed.

Problem 3

The perovskite films show inhomogeneous film morphology after the thermal annealing process, and PSCs based on them demonstrate inferior device performance.

Potential solution

Purge the glovebox for 30 min before starting any film deposition. In addition, the maximum storage time for CsI/PbI2 precursor solutions is up to two days. Prepare a new precursor solution if the precursors are stored for more than three days. Keep in mind that do not filter CsI/PbI2 precursor solutions before use.

Problem 4

The coverage of spherical crystals on perovskite film is poor after deposition of 100 mM-terpyridine solution.

Potential solution

Prepare a fresh terpyridine solution instead and shorten the stirring time of terpyridine solution.

Problem 5

Particles are visible after spiro-OMeTAD solution spin-coating.

Potential solution

Filter the spiro-OMeTAD solution or prepare a fresh one instead.

Problem 6

The reproducibility of PSCs is poor from batch to batch.

Potential solution

There are some suggestions to improve repeatability: (1) fully purge the chamber of the spin-coater before depositing different solutions. (2) When annealing perovskite in air, control the relative humidity not less than 30% and not more than 40%. (3) Try not to change brands and batches of perovskite precursor drugs. (4) Solvents are used in separate packages and regularly renewed to minimize the probability of contamination.

Problem 7

The PCEs of terpyridine-treated PSCs are lower than that of the untreated reference device, especially in the lower FF.

Potential solution

There are two scenarios: If it is also observed that the spiro-OMeTAD film has a bright green color after spin-coating, increase its spin-coating speed from 3000 rpm to 4000 rpm. If terpyridine does not form spherical crystals or forms aspheric crystals, purify the terpyridine or change the brand or batch of the drug product.

Problem 8

Device suddenly dies during stability testing.

Potential solution

Keep in mind that not every PSC can end up giving a time-PCE curve, as electrode rubbing occasionally occurs and repeated clamping of the test fixture can damage the electrodes. For devices intended for stability testing, eliminating the molybdenum oxide layer when depositing top electrodes can improve device stability. In addition, for greater probability of obtaining a time-PCE curve, prepare as many devices as the holder space allows.

Resource availability

Lead contact

Further information and requests for resources and reagents should be directed to and will be fulfilled by the lead contact, Rui Wang (wangrui@westlake.edu.cn).

Technical contact

Further information and requests for experimental details could be directed to and will be fulfilled by the technical contact, Sisi Wang (wangsisi@westlake.edu.cn).

Materials availability

This study did not generate new unique reagents.

Data and code availability

No data or code was generated in this study.

Acknowledgments

This work has received the funding from State Key Laboratory of Silicon Materials and Advanced Semiconductor Materials (SKL2022-07 ) and the support of the Research Center for Industries of the Future and the startup funding provided by Westlake University. The authors also acknowledge the grant (LD22E020002 ) from the Natural Science Foundation of Zhejiang Province of China, the support of the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (grant no. 61721005 ), and the startup funding received from Zhejiang University. S.W. also acknowledges the grant from the China Postdoctoral Science Foundation (G14436582201 ).

Author contributions

S.W. conducted experiments and wrote the manuscript under the supervision of J.X. and R.W. J.S. contributed to picture designs. All authors contributed to the draft and prepared the final version.

Declaration of interests

The authors declare no competing interests.
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