Dipole-field-assisted charge extraction in metal-perovskite-metal back-contact solar cells
Xiongfeng Lin, Askhat N. Jumabekov, Niraj N. Lal, Alexander R. Pascoe, Daniel E. Gómez, Noel W. Duffy, Anthony S.R. Chesman, Kallista Sears, Maxime Fournier, Yupeng Zhang, Qiaoliang Bao, Yi-Bing Cheng, Leone Spiccia & Udo Bach
Nature Commun. 8 (2017) 613
1 Department of Materials Science & Engineering, Monash University, Clayton, VIC 3800, Australia.
2 CSIRO Manufacturing, Clayton, VIC 3168, Australia.
3 Plasmonics & Photochemistry Laboratory, RMIT University, Melbourne, VIC 3000, Australia.
4 CSIRO Energy, Clayton, VIC 3168, Australia.
5 ARC Centre of Excellence in Exciton Science, Monash University, Clayton, VIC 3800, Australia.
6 School of Chemistry and ARC Centre of Excellence in Electromaterials Science, Monash University, Clayton, VIC 3800, Australia.
7 College of Electronic Science and Technology, Shenzhen University, Shenzhen 518000, China.
8 Melbourne Centre for Nanofabrication, Clayton, VIC 3800, Australia.
9 Department of Chemical Engineering, Monash University, Clayton, VIC 3800, Australia
Hybrid organic-inorganic halide perovskites are low-cost solution-processable solar cell materials with photovoltaic properties that rival those of crystalline silicon. The perovskite films are typically sandwiched between thin layers of hole and electron transport materials, which efficiently extract photogenerated charges. This affords high-energy conversion efficiencies but results in significant performance and fabrication challenges. Herein we present a simple charge transport layer-free perovskite solar cell, comprising only a perovskite layer with two interdigitated gold back-contacts. Charge extraction is achieved via self-assembled monolayers and their associated dipole fields at the metal-perovskite interface. Photovoltages of ~600 mV generated by self-assembled molecular monolayer modified perovskite solar cells are equivalent to the built-in potential generated by individual dipole layers. Efficient charge extraction results in photocurrents of up to 12.1 mA cm−2 under simulated sunlight, despite a large electrode spacing.
Fig. 1 Kelvin-probe-force-microscopy of an interdigitated gold microelectrode array during molecular modification. Contact potential difference (CPD) maps across sets of interdigitated fingers and illustrations of the KPFM imaging experiment for an unmodified IDA a + b, an IDA after exposure to 4-methoxythiophenol (OMeTP) and its subsequent electrochemical desorption from electrode “b” c + d, and an IDA after the final modification step with 4-chlorothiophenol (ClTP) e + f
Fig. 2 Back-contact metal-perovskite-metal solar cells. a Schematic energy band diagram of a metal-perovskite-metal solar cell at thermal equilibrium in the dark. The work function of the methylammonium lead iodide (MAPbI3) perovskite (qϕp) is situated between those of the metal electrodes “a” (qϕðaÞ m ) and “b” (qϕðbÞ m ). The overall built-in potential of the solar cell is equal to the sum of the built-in potentials at the metalperovskite contacts. qχper corresponds to the electron affinity of MAPbI3. b Cross-section diagram of a dipole self-assembled monolayer (SAM) modified back-contact gold-perovskite-gold solar cell. Electrode “a” (anode, left) is modified with a molecular monolayer of 4-methoxythiophenol (OMeTP) with a molecular dipole of −2.67D. Electrode “b” (cathode, right) is modified with a monolayer of 4-chlorothiophenol (ClTP) with a molecular dipole of + 1.41 D
Fig. 3 Photovoltaic properties of self-assembled monolayer modified back-contact perovskite solar cells. a J–V curves of a dipole-modified gold-perovskite-gold bc-PSC measured under standard solar irradiation (AM 1.5 G, 1000Wm−2), reverse scan (solid blue, encapsulated; solid red, unencapsulated) and forward scan (dashed blue, encapsulated, dashed red, unencapsulated). b Spectral response (External quantum efficiency – EQE, solid line) and the corresponding integrated short-circuit current density (dashed line) of a SAM-modified PSC. c Time evolution of the maximum power point photocurrent density (JMPP) of a SAM-modified (red) and poled, unmodified bc-PSC (black) and their power output d