Understanding the Photovoltaic Performance of Perovskite–Spirobifluorene Solar Cells

Abstract

Lead halide perovskite solar cells with remarkable power conversion efficiency have attracted much attention in recent years. However, there still exist many problems with their use that are not completely understood, and further studies are needed. Herein, the hole-transport layer dependence of the photovoltaic performance of perovskite solar cells is investigated in detail. It is found that devices freshly prepared using pristine 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) and Li-doped spiro-OMeTAD as hole-transport layers exhibit S-shaped current density-voltage curves with poor fill factors. The devices show progressively improved fill factors and efficiencies upon exposure to air, which is attributed to air-induced conductivity improvement in the spiro-OMeTAD layer. After introducing a cobalt salt dopant (FK209) into the spiro-OMeTAD layer, the corresponding devices show remarkable performance without the need of air exposure. These results confirm that the dopant not only increases the conductivity of spiro-OMeTAD layer, but also tunes the surface potential, which helps to improve charge transport and reduce the recombination loss.

Planar Perovskite Solar Cells with High Open‐Circuit Voltage Containing a Supramolecular Iron Complex as Hole Transport Material Dopant

“…It was observed that Fe(ttb) doping increases the conductivity, although not as strongly as FK209 (Figure S2). Spiro‐MeOTAD films containing LiTFSI and TBP show already enhanced conductivity,, according to the literature in particular when exposed to oxygen, whereas oxygen exposure is not required when FK209 is added …”

“…Spiro-MeOTAD films containing LiTFSI and TBP show already enhanced conductivity, [37,38] according to the literature in particular when exposed to oxygen, whereas oxygen exposure is not required when FK209 is added. [54] Photoelectron spectroscopy measurements were performed to evaluate the doping effect in terms of a shifted work function. To mimic the configuration of the later solar cell stack, HTM layers (spiro-OMeTAD with LiTFSI and TBP) containing different doping concentrations of Fe(ttb) (0, 3 and 5 mol %) and FK209 (3 mol %) were deposited onto perovskite films.…”

Tuning Bandgap of Mixed‐Halide Perovskite for Improved Photovoltaic Performance Under Monochromatic‐Light Illumination

“…To obtain the TiO 2 nanocrystal (nano‐TiO 2 ) colloidal solution (≈5 mg/mL), the TiO 2 nanocrystals were dispersed into anhydrous chloroform and anhydrous methanol (1:1 volume ratio), and nano‐TiO 2 was synthesized by using the method as reported previously . The spiro‐OMeTAD precursor solution (54.36 mg mL −1 ) was prepared by dissolving spiro‐OMeTAD (72.3 mg, Lumtec) in anhydrous chlorobenzene (1.33 mL, Sigma–Aldrich), 28.8 µL of anhydrous 4‐tert‐butylpyridine (TBP) (Sigma–Aldrich), 17.5 µL of lithium‐bis(trifluoromethanesulfonyl) imide (Li‐TFSI) in acetonitrile (520 mg/mL), and 60 µL of cobalt salt tris[2‐(1H‐pyrazol‐1‐yl)‐4‐tertbutylpyridine] cobalt(III) tris[bis(trifluoromethylsulfonyl)imide] (FK209) in acetonitrile (100 mg mL −1 ) were added into spiro‐OMeTAD solution obtained above . Note that the weighing and dissolution of these materials were performed in a nitrogen‐filled glove box, and the solutions were stirred at least 12 h before use.…”

A new approach to predict the formation of 3D hybrid organic‐inorganic perovskites

“…Perovskite refers to a three‐dimensional (3D) structure for a class of materials with chemical formula ABX 3 (A and B are the cations and X is oxygen or halide) . Perovskites that form with the organic and inorganic constituents are known as hybrid organic‐inorganic perovskites (HOIPs) . Due to extraordinary optical properties, for example, emission, absorption, and tunable optical band gap (visible to infrared), the HOIPs materials are mostly used for photovoltaic applications .…”

“…[1][2][3][4] Perovskites that form with the organic and inorganic constituents are known as hybrid organic-inorganic perovskites (HOIPs). [2,3,[5][6][7][8][9] Due to extraordinary optical properties, for example, emission, absorption, and tunable optical band gap (visible to infrared), the HOIPs materials are mostly used for photovoltaic applications. [2,5,[10][11][12][13] The properties of perovskite materials can be varied by replacing A, B, or X sites with a suitable protonated organic molecule, divalent metal cations, and halogens, respectively.…”