Fig. 1. Transmittance of PTAA on (a) ITO glass and on (b) electronic grade pure glass; SEM (scale bar=1  μm) images of (c) ITO glass and (d) PTAA precursor covered ITO glass. XPS profiles for PTAA, PTAA+DMF, PTAA+DMF/CB, and PTAA+DMF/toluene on ITO substrate: (e) scan for O 1s; (f) scan for N 1s.

Fig. 2. AFM phase images (500  nm×500  nm) of (a) ITO/PTAA, (b) ITO/PTAA/DMF, (c) ITO/PTAA/DMF/toluene, and (d) ITO+PTAA/DMF/CB. (Insets show the 3D morphology for each film and RMS reflects the film roughness.)

Fig. 3. (a)–(c) Cross-sectional SEM images for devices with PTAA, PTAA/DMF/CB, and PTAA/DMF/toluene as HTLs, respectively. (d)–(h) Top-view SEM images of perovskite film on glass/PTAA, glass, glass/PTAA/DMF/toluene, glass/PTAA/DMF, and glass/PTAA/DMF/CB. (Red circles show pin holes.) (i)–(l) Contact angles for (i) PTAA; (j) PTAA/DMF; (k) PTAA/DMF/CB, and (l) PTAA+DMF/toluene on glass.

Fig. 4. Top-view AFM images (1  μm×1  μm) of perovskites on PTAA with different solvent modification during (rotating state) or after spin coating of DMF (stable state): (a) glass/PTAA/DMF/toluene (drop under stable state)+PSK; (b) glass/PTAA/PSK; (c) glass/PTAA/DMF/toluene (drop while rotating)/PSK; (d) glass/PTAA/DMF/PSK; (e) glass+PTAA/DMF/CB (drop while rotating)/PSK; (f) glass+PTAA/DMF/CB (drop under stable state)/PSK.

Fig. 5. (a) XRD patterns and (b) UV-vis absorption spectra for PTAA/PSK, PTAA/DMF/PSK, PTAA/DMF/CB/PSK, and PTAA/DMF/toluene/PSK on ITO substrates. (c) Steady-state PL and (d) TRPL spectra for PSCs corresponding to the films in (a) and (b).

Fig. 6. (a) J-V curve under 1.5G sunlight through a solar simulator by reverse scan for PSCs using PTAA with different concentrations (device structure: ITO/PTAA/PSK/PCBM/BCP/Ag). (b) Best device based on toluene-treated PTAA. (c) to (g) J-V curves for devices based on different PTAA substrates by reverse and forward scans: (d) PTAA without any treatment; (e) PTAA treated with DMF; (f) PTAA treated with DMF/CB. The active area for the above cells is 0.05  cm2.

Fig. 7. (a) Device structure. (b) Enlarged drawing of toluene between PTAA and perovskite. (c) Energy-level diagram of each layer in the device. (d) Fabrication process of PSCs based on DMF/toluene-treated PTAA. (e) J-V curves (by reverse scan) for the devices in this research. (f) Nyquist plot for PSCs with pristine PTAA and PTAA treated by DMF, DMF/CB, and DMF/toluene, respectively (bias voltage=0.6  V, frequency in range of 0.1–100 Hz). (g) IPCE curves of PSCs by using PTAA, PTAA/DMF, PTAA/DMF/CB, and PTAA/DMF/toluene as HTLs. (h) Long-term stability test for PSCs fabricated based on PTAA treated by different solvents in ambient with humidity above 35% and temperature around RT.

Fig. 8. Data difference analysis for 36 PSCs by using toluene-treated PTAA as hole transport material in inverted structure.

Fig. 9. Photovoltaic parameters of the best device (with DMF/toluene modified PTAA as HTL) newly prepared as well as after storage in N2-filled glove box for 10 and 20 days (measured under continuous 1.5G light illumination, 30 s once, in ambient). Relationships between exposure time and exposure time and (a) efficiency, (b) Jsc, (c) Voc, and (d) FF, respectively.

Table 1. Film Thickness Measurement Result by a Step Profiler

Table 2. Contact Angle Measurement Results Corresponding to PTAA with Different Solvent Treatment^a

Table 3. TRPL Time Decay Analysis Through Double Exponential Fitting Method

Table 4. Long-Term Stability for Devices with Pristine PTAA Compared with PTAA Treated by DMF, DMF/Toluene, and DMF/CB, with Different Storage Times

Table 5. Photovoltaic Parameters of the Best Solar Cell with Toluene-Treated PTAA as HTL at Different Storage Times (Measured 21 Times, 30 s Once Under Continuous 1.5G Sunlight Without Encapsulation)