Chapter 3: Experimental Procedures
3.2 Device fabrication
3.2.1. Device fabrication using air crystallized perovskite film
The planar device structure adopted for fabricating perovskite solar cells consists of bottom electrode indium tin oxide (ITO), PEDOT:PSS as hole transport layer (HTL), light absorbing perovskite layer, PC60BM as electron transport layer (ETL), rhodamine as thin interfacial layer and top metal electrode silver (Ag) [98]. Pre-patterned indium tin oxide (ITO) glass substrates were numbered and placed in a Teflon sample holder. The sample holder was immersed in a beaker and ultrasonically cleaned sequentially with detergent water, deionized water, acetone and isopropanol solvents for 20 minutes each.
After ultrasonic cleaning the substrates were dried in a stream of nitrogen gas and placed into RF surface plasma cleaner (PDC-32G). Plasma cleaner was placed into low vacuum (10-2 Torr) and was purged with oxygen gas after 5 minutes. Then the RF coils were given medium power to generate a purple colored oxygen plasma. After 25 minutes of oxygen plasma cleaning the chamber was vented with air to remove the plasma cleaned
samples. PEDOT:PSS was spin coated at 4500 rpm for 90 sec, followed by annealing in air at 135 ºC for 5 min. The samples were then transferred inside a N2 filled glove box for coating with the perovskite layer. A mixed solution of 581 mg of PbI2 (1.26 M ) and 209 mg of CH3NH3I (1.3 M) mixed overnight in 1 ml of γ-butyrolactone : DMSO in 7:3 volume ratio was spin coated at 750 rpm for 20 sec and 4000 rpm for 60 sec, with 160 µl toluene dripped at the middle of total spinning time (40 sec). The films were then
crystallized by either thermal annealing (100 ºC, 20 min) or keeping the films in ambient air for different periods of time (1 h, 3 h, 5 h, 8 h, and 10 h). Figure 3.1 shows the
perovskite spin coating steps with toluene dripping and its post crystallization in ambient air at room temperature leading to nanorod features. PC60BM (20 mg/ml in
chlorobenzene) was then spin coated on top of the perovskite layer at 2000 rpm for 40 sec and then kept for 15 min inside the glove box for solvent drying at ambient temperature.
Rhodamine (0.5 mg/ml in isopropyl alcohol) was then spin coated at 4000 rpm for 40 sec on top of the PC60BM layer. Ag (100 nm) electrode was then deposited using thermal evaporation in high vacuum of 2×10-6 mbar. The solar cell active area was 0.16 cm2, as defined by the shadow mask.
Figure 3.1 Schematic showing deposition of perovskite nanorod film by spin coating followed by crystallization in ambient air at room temperature.
Nanorod formation in ambient air at room temperature
3.2.2. Device fabrication using perovskite film prepared by slow crystallization in N2
ambient followed by ambient environment exposure at room temperature.
The planar device structure adopted for fabricating perovskite solar cells consists of bottom electrode indium tin oxide (ITO), PEDOT:PSS as hole transport layer (HTL), light absorbing perovskite layer, PC60BM as electron transport layer (ETL), rhodamine as thin interfacial layer and top metal electrode silver (Ag) [98]. Pre-patterned indium tin oxide (ITO) glass substrates were numbered and placed in a Teflon sample holder. The sample holder was immersed in a beaker and ultrasonically cleaned sequentially with detergent water, deionized water, acetone and isopropanol solvents for 20 minutes each.
After ultrasonic cleaning the substrates were dried in a stream of nitrogen gas and placed into RF surface plasma cleaner (PDC-32G). Plasma cleaner was placed into low vacuum (10-2 Torr) and was purged with oxygen gas after 5 minutes. Then the RF coils were given medium power to generate a purple colored oxygen plasma. After 25 minutes of oxygen plasma cleaning the chamber was vented with air to remove the plasma cleaned samples. PEDOT:PSS was spin coated at 4500 rpm for 90 sec, followed by annealing in air at 135 ºC for 5 min. The samples were then transferred inside a N2 filled glove box for coating with the perovskite layer. A mixed solution of 581 mg of PbI2 (1.26 M ) and 209 mg of CH3NH3I (1.3 M) mixed overnight in 1 ml of γ-butyrolactone : DMSO in 7:3 volume ratio was spin coated at 750 rpm for 20 sec and 4000 rpm for 60 sec, with 160 µl toluene dripped at the middle of total spinning time (40 sec). The films were then
crystallized by either thermal annealing (100 ºC, 20 min) or keeping the films in ambient air for 5 h at room temperature or by first keeping the perovskite film in nitrogen (N2) ambient for 1 h, 2 h, 3 h followed by 5 h in ambient atmosphere having 40% RH.
PC60BM (20 mg/ml in chlorobenzene) was then spin coated on top of the perovskite layer at 2000 rpm for 40 sec and then kept for 15 min inside the glove box for solvent drying at ambient temperature. Rhodamine (0.5 mg/ml in isopropyl alcohol) was then spin coated at 4000 rpm for 40 sec on top of the PC60BM layer. Ag (100 nm) electrode was then deposited using thermal evaporation in high vacuum of 2×10-6 mbar. The solar cell active area was 0.16 cm2, as defined by the shadow mask.
3.2.3. Device fabrication using perovskite film prepared by using water as co- precursor solvent
The planar device structure adopted for fabricating perovskite solar cells consists of bottom electrode indium tin oxide (ITO), PEDOT:PSS as hole transport layer (HTL), light absorbing perovskite layer, PC60BM as electron transport layer (ETL), rhodamine as thin interfacial layer and top metal electrode silver (Ag) [98]. Pre-patterned indium tin oxide (ITO) glass substrates were numbered and placed in a Teflon sample holder. The sample holder was immersed in a beaker and ultrasonically cleaned sequentially with detergent water, deionized water, acetone and isopropanol solvents for 20 minutes each.
After ultrasonic cleaning the substrates were dried in a stream of nitrogen gas and placed into RF surface plasma cleaner (PDC-32G). Plasma cleaner was placed into low vacuum (10-2 Torr) and was purged with oxygen gas after 5 minutes. Then the RF coils were given medium power to generate a purple colored oxygen plasma. After 25 minutes of oxygen plasma cleaning the chamber was vented with air to remove the plasma cleaned samples. PEDOT:PSS was spin coated at 4500 rpm for 90 sec, followed by annealing in air at 135 ºC for 5 min. The samples were then transferred inside a N2 filled glove box for coating with the perovskite layer. A mixed solution of 581 mg of PbI2 (1.26 M ) and 209
mg of CH3NH3I (1.3 M) mixed overnight in 1 ml of γ-butyrolactone (GBL) : DMSO in 7:3 volume ratio with addition of different concentration of de-ionised water (1, 2, 3, 4, 5, 10, 15, 20, 25 vol. % ) as a co-solvent along with GBL and DMSO, was spin coated at 750 rpm for 20 sec and 4000 rpm for 60 sec, with 160 µl toluene dripped at the middle of total spinning time (40 sec). The films were then crystallized by thermal annealing at temperature (80 ºC, 10 min). PC60BM (20 mg/ml in chlorobenzene) was then spin coated on top of the perovskite layer at 2000 rpm for 40 sec and then kept for 15 min inside the glove box for solvent drying at ambient temperature. Rhodamine (0.5 mg/ml in isopropyl alcohol) was then spin coated at 4000 rpm for 40 sec on top of the PC60BM layer. Ag (100 nm) electrode was then deposited using thermal evaporation in high vacuum of 2×10-6 mbar. The solar cell active area was 0.16 cm2, as defined by the shadow mask.