Monolithic Perovskite‐CIGS Tandem Solar Cells via In Situ Band Gap Engineering

Abstract

lead iodide perovskite top cell on Cu 2 ZnSn(S,Se) 4 kesterite and Si-based bottom cells. [ 10,12 ] The remarkable effi ciencies of perovskite devices above 15%, the possibility to process at temperatures below 150 °C, and the highly tunable band gap range from 1.6 to 2.25 eV make these materials especially attractive for monolithic tandem integration with CIGS. [12][13][14][15][16][17][18][19][20] Here, we report perovskite-CIGS tandem solar cells in which each cell was customized for monolithic integration in the following sequence: transparent conducting electrode (TCE)/phenyl-C61-butyric acid methyl ester (PCBM)/perovskite/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/ITO/CdS/CIGS/Mo/Si 3 N 4 /glass. By modifying our solution-based process, [ 21 ] the CIGS absorber band gap was reduced to 1.04 eV for improved photon management. A 30 nm thick ITO was selected as a transparent recombination layer that was deposited directly onto the CdS without the intrinsic ZnO layer commonly used in CIGS devices. The elimination of ZnO from the device structure was critical for achieving functional perovskite tandems, as we discovered that the presence of ZnO in proximity to the perovskite layer degrades device performance. Perovskite devices with electron-selective ZnO layers have been reported previously, [22][23][24] however we found that processing at temperatures above 60 °C resulted in deterioration of the perovskite layer. In contrast, perovskite layers processed on our ZnO-free CIGS structure could withstand annealing treatments for several hours at 120 °C without any damage.Considering the importance of precise band gap control in monolithic tandem devices, we designed a reactor for continuous in situ monitoring and precise control of the optical properties of the perovskite layer via vapor-based halide exchange reactions, as illustrated in Figure 1 a. The system provided temperature and pressure control as well as spectroscopic measurement capability. In a typical process, a sample of spincoated lead halide PbX 2 (X = I and/or Br) is placed inside the temperature-controlled vacuum chamber and annealed in the presence of methylammonium halide (CH 3 NH 3 X) vapor. A transparent port at the top of the chamber provides an optical path for a broad-spectrum light source to illuminate the sample in the reactor, and a port beneath the sample leads to a spectrophotometer, which collects the transmission spectra. The real-time feedback is used for precise engineering of the perovskite absorber properties by adjusting the temperature, pressure, and precursor type. The process was designed to have better compatibility with the CIGS device than previously reported vapor-assisted approaches that employ temperatures in excess of 120 °C and focus on pure iodide perovskite with fi xed band gap. [ 25,26 ] In our reactor the conversion temperature was

Solution-processed chalcopyrite–perovskite tandem solar cells in bandgap-matched two- and four-terminal architectures

“…S9), which is the highest reported value for a solution-processed two-terminal tandem device, exceeding HP/HP tandem devices of 17.0%, 35 HP/polymer tandem devices of up to 16%, 58 and HP/chalcogenide tandems up to 15.9%. 38 The excellent current matching of our solution processed low-bandgap CIS cell with our highly efficient, NIR-transparent MAPbI3 perovskite cells is accountable for this high two-terminal performance that exceeds even some recent reports of two-terminal devices with 1.1 eV bandgap silicon or 1.2 eV bandgap perovskite bottom cells. 35,59 Conclusions Measurements of both CIS and CIGS solar cells at reduced irradiance and UV-and visible filtered light elucidate their suitability as bottom cells in tandem devices.…”

“…35 However, the large bandgap of the Sn-based bottom cell absorber of 1. 2 38 While these values are noteworthy, tandem devices were limited by low transmission or high resistance of the employed electrodes or reduced efficiencies of the small bandgap bottom cells.…”

“…31,32,35,38 The used chalcogenide cells exhibited PCEs of 14.3% for CIGS and 13.0% for low-bandgap CIS absorbers, which is the highest reported PCE for a solution-processed solar cell with a bandgap of 1.0 eV. 39 When we measured the performance of our chalcogenide devices with the above described perovskite filters, reducing the irradiance and the UV-and visible portion of the light, the current density and efficiency (uncorrected for reduced irradiance) dropped roughly to a third due to the 31-37% total transmission of the perovskites filters.…”

Too Many Junctions? A Case Study of Multijunction Thin‐Film Silicon Solar Cells

“…Moreover, hybrid tandem solar cells integrating different photovoltaic technologies have drawn more and more attention over the past years in the pursuit of higher efficiencies. To name a few notable examples, the perovskite/ crystalline silicon tandem, [21][22][23][24] perovskite/copper indium gallium selenide (CIGS) tandem [25] and hydrogenated amorphous silicon (a-Si:H)/organic double-and triple-junction solar cells [26] have all demonstrated the potential of exceeding the efficiency of the component single-junction cells. When the absolute efficiency is the main concern, making multijunction solar cells is the inevitable trend.…”

Progress, challenges and perspectives in flexible perovskite solar cells

“…45 The tandem configuration should be able to increase the PCE by 20% (bringing it to over 30% in absolute terms) 46 but the best published reports are still well below this target. [46][47][48][49][50][51] Apart from the high PCEs delivered, the key advantage of this new PV technology consists in the possibility of relatively simple processing of the perovskite precursors either via vapour techniques or in solution (i.e. via printing techniques) requiring low temperatures to convert into their final semiconducting form (o150 1C).…”