Lead Halide Perovskite Photovoltaic as a Model p–i–n Diode

Abstract

The lead halide perovskite photovoltaic cells, especially the iodide compound CH3NH3PbI3 family, exhibited enormous progress in the energy conversion efficiency in the past few years. Although the first attempt to use the perovskite was as a sensitizer in a dye-sensitized solar cell, it has been recognized at the early stage of the development that the working of the perovskite photovoltaics is akin to that of the inorganic thin film solar cells. In fact, theoretically perovskite is always treated as an ordinary direct band gap semiconductor and hence the perovskite photovoltaics as a p-i-n diode. Despite this recognition, research effort along this line of thought is still in pieces and incomplete. Different measurements have been applied to different types of devices (different not only in the materials but also in the cell structures), making it difficult to have a coherent picture. To make the situation worse, the perovskite photovoltaics have been plagued by the irreproducible optoelectronic properties, most notably the sweep direction dependent current-voltage relationship, the hysteresis problem. Under such circumstances, it is naturally very difficult to analyze the data. Therefore, we set out to make hysteresis-free samples and apply time-tested models and numerical tools developed in the field of inorganic semiconductors. A series of electrical measurements have been performed on one type of CH3NH3PbI3 photovoltaic cells, in which a special attention was paid to ensure that their electronic reproducibility was better than the fitting error in the numerical analysis. The data can be quantitatively explained in terms of the established models of inorganic semiconductors: current/voltage relationship can be very well described by a two-diode model, while impedance spectroscopy revealed the presence of a thick intrinsic layer with the help of a numerical solver, SCAPS, developed for thin film solar cell analysis. These results point to that CH3NH3PbI3 is an ideal intrinsic semiconductor, which happens to be very robust against accidental doping, and that the perovskite photovoltaic cell is in fact a model p-i-n diode. The analytical methods and diagnostic tools available in the inorganic semiconductor PV cells are useful and should be fully exploited in the effort of improving the efficiency. One outstanding question is why the perovskite stays intrinsic. Considering the defects and impurities that must abound in the perovskite layers formed by the spin-coating process, for example, there must be physicochemical mechanism keeping it from being doped. This may be related to the special band structure making up the band gap in this ionic solid. Understanding the mechanism may open a door for the wider utility of this class of solid.

Effect of Carrier Transport in NiO on the Photovoltaic Properties of Lead Iodide Perovskite Solar Cells

“…The J-V curve of the cells containing PEDOT:PSS is ideally fitted by the one or two diode models. 14,15 Therefore, in case of PEDOT:PSS, we assumed that the electrons in the conduction band of the perovskite directly recombine with the hole in the valence band of PEDOT:PSS, or recombine through the in-gap recombination centers in the bulk perovskite (the ShockleyRead-Hall mechanism). On the other hands, the J-V curve of the cells containing NiO x is not ideal.…”

“…1,2 Planar type perovskite solar cells have been developed to circumvent the complicated analysis of perovskite semiconductor in mesoporous structure, and to produce the perovskite solar cells via lower temperature processes. [7][8][9][10][11][12][13][14][15][16][17][18] We have demonstrated that the solar cells consisting of Tin-doped indium oxide (ITO)/Poly (3,4-ethylenedioxythiophene): Poly(styrenesulfonate) (PEDOT:PSS)/Perovskite/Phenyl-C61-Butyric-Acid-Methyl Ester (PCBM)/Ag ( Fig. 1) have the ideal diode properties and high reproducibility.…”

“…1) have the ideal diode properties and high reproducibility. [14][15][16][17][18] From the Mott-Schottky plot, the perovskite solar cells can be considered as pin structure, consisting of p-type/ intrinsic/n-type semiconductors. 15 Recently, several hole transport materials (HTM) have also been introduced into the perovskite solar cells in place of PEDOT:PSS to obtain probable device application or efficient devices.…”

“…[14][15][16][17][18] From the Mott-Schottky plot, the perovskite solar cells can be considered as pin structure, consisting of p-type/ intrinsic/n-type semiconductors. 15 Recently, several hole transport materials (HTM) have also been introduced into the perovskite solar cells in place of PEDOT:PSS to obtain probable device application or efficient devices. [19][20][21][22][23][24][25][26][27][28][29][30][31][32] The typical requirements for HTMs of perovskite solar cells are as follows.…”

Review—Organic Materials for Thermoelectric Energy Generation

“…Organic-inorganic lead halide perovskites with ABX 3 structure are found to be intrinsic semiconductor materials 127 and so doping may be required to impart p-type or n-type behavior. Replacement of the one or more of the A and B cations, or the X anion has resulted in bandgap tuning and stability improvements.…”