Vacuum‐Assisted Growth of Low‐Bandgap Thin Films (FA_0.8MA_0.2Sn_0.5Pb_0.5I₃) for All‐Perovskite Tandem Solar Cells

Abstract

enormous interest in perovskite-based multi-junction photovoltaics (PV). [1] To go beyond Shockley-Queisser radiative efficiency limit for single-junction solar cells, wide-bandgap (WBG) perovskite top solar cells (E G > 1.6 eV) [5] are combined with high-efficiency low-bandgap (LBG) bottom solar cells made from Si, [6] CIGS [7] or LBG (E G < 1.3 eV) perovskite devices. [8][9][10] While tandem PV technologies based on market-dominant crystalline Si and CIGS bottom solar cells have recently demonstrated PCEs exceeding 28%, [6,11] all-perovskite tandem solar cells are still less advanced. In comparison to single junction PSCs, all-perovskite tandem solar cells still lack behind with record PCEs of 23.1% [12] and 25% [12] for of all-perovskite two-terminal (2T) and four-terminal (4T) tandem solar cells, respectively.The key challenges hindering the progress of all-perovskite tandem solar cells are the low performance and stability of the LBG perovskite bottom solar cells. To resolve these challenges, previous studies on LBG perovskite thin films addressed compositional engineering of the perovskite, strategies to improve the thin-film morphology, and routes to enhance the optical and electrical properties. [8,10,[12][13][14][15] LBG All-perovskite multijunction photovoltaics, combining a wide-bandgap (WBG) perovskite top solar cell (E G ≈1.6-1.8 eV) with a low-bandgap (LBG) perovskite bottom solar cell (E G < 1.3 eV), promise power conversion efficiencies (PCEs) >33%. While the research on WBG perovskite solar cells has advanced rapidly over the past decade, LBG perovskite solar cells lack PCE as well as stability. In this work, vacuum-assisted growth control (VAGC) of solution-processed LBG perovskite thin films based on mixed Sn-Pb perovskite compositions is reported. The reported perovskite thin films processed by VAGC exhibit large columnar crystals. Compared to the well-established processing of LBG perovskites via antisolvent deposition, the VAGC approach results in a significantly enhanced charge-carrier lifetime. The improved optoelectronic characteristics enable high-performance LBG perovskite solar cells (1.27 eV) with PCEs up to 18.2% as well as very efficient four-terminal all-perovskite tandem solar cells with PCEs up to 23%. Moreover, VAGC leads to promising reproducibility and potential in the fabrication of larger active-area solar cells up to 1 cm 2 .In recent years, hybrid organic-inorganic perovskite materials attracted tremendous attention due to their outstanding optoelectronic and piezoelectric properties. [1][2][3] The optoelectronic properties of the perovskite materials enables power conversion efficiencies (PCEs) as high as 25.2% in singlejunction perovskite thin-film solar cells. [4] Moreover, the wide range of bandgaps (E G ) of this class of materials generates Adv. Energy perovskite thin films are realized by careful compositional engineering, incorporating Sn at the site of Pb in multication perovskite crystal structures. [8,10,13] In this regard, the exact ratio of Sn to Pb is criti...

Triple-cation low-bandgap perovskite thin-films for high-efficiency four-terminal all-perovskite tandem solar cells

“…15 In a previous publication, we introduced the vacuumassisted growth control (VAGC) method as an efficient strategy to process pin-hole free Sn-based perovskite thin-lms. 16 Applying the same method here, we prepare mixed Sn-Pb perovskite thin-lms in the composition Cs x (FA 0.8 MA 0.2 ) (1Àx) -Sn 0.5 Pb 0.5 I 3 with x ¼ 0%, 1%, 2.5%, 5%, and 10%, hereaer denoted as Cs0%, Cs1%, Cs2.5%, Cs5% and Cs10%, respectively. The experimental section provides the reader with more details on the PSC devices and perovskite thin-lms fabrication.…”

“…Therefore, this class of materials is suited for both WBG top and LBG bottom solar cells in an all-perovskite tandem solar cell (all-PTSC) conguration. [9][10][11][12][13][14][15][16] All-PTSCs with current record PCEs of 25.4% for a 4T 17 and 24.8% for a 2T 18 conguration benet from simple and potentially cost-effective fabrication processes via both solution 19 and vapor 20,21 deposition methods. However, to date, the low operational stability and performance of LBG bottom PSCs is one of the major hurdles towards high-efficiency all-PTSCs.…”

Perovskite‐Based Tandem Solar Cells: Get the Most Out of the Sun

“…Contour plots of 2T tandem a) J sc and b) V oc in perovskite/perovskite tandem devices as a function of top and bottom absorber thickness (data were analyzed based on Table 3). [191] 4T FA [192] 2T FA [193] a)…”

Choose Your Own Adventure: Fabrication of Monolithic All‐Perovskite Tandem Photovoltaics

“…In general, while the low‐ E g Sn/Pb alloyed perovskites do not have particularly high % V OC‐SQ , with two solar cells reaching ≥90%, [ 219,220 ] the % J SC‐SQ is most notably also generally poor, with only four solar cells reaching ≥85%, [ 36,51,129,130 ] by achieving, for example, 32 mA cm −2 for a ≈1.25 eV perovskite. [ 130 ] For comparison, the rest are ≈80% [ 4,36,48,52,131,132,221–223 ] or below. This is in contrast to both mid‐ E g [ 30,37,104,110,122,123,224–227 ] and wide‐ E g [ 30,31,70,101,102,224,228 ] perovskite devices that have regularly reached a % J SC‐SQ of ≥90% (Figure 10B).…”