Inverted Tandem Polymer Solar Cells with Polyethylenimine‐Modified MoO_X/Al₂O₃:ZnO Nanolaminate as the Charge Recombination Layers

Abstract

having broader absorption ranges, which span a larger portion of the solar spectrum. [ 5,6 ] Nevertheless, organic semiconductors used in PSCs having a single BHJ layer still present narrow absorption ranges that cover only a fraction of the solar spectrum; leaving more than 60% of the total photons unabsorbed. [ 7 ] Furthermore, the maximum thickness of this BHJ layer allowable for high effi ciency is limited by the transit-time of carriers within this layer. For a given set of materials and processing conditions, the optimum BHJ layer thickness strikes the best compromise between maximizing photon absorption and charge collection. [ 8 ] To overcome the limitations of PSCs with a single BHJ layer, two or more PSCs having BHJ active layers with complementary absorption ranges are connected in series by stacking them on top of one another. These so-called tandem solar cells can achieve higher power conversion effi ciency (PCE) values than single BHJ layer PSCs because they cumulatively absorb a larger portion of the solar spectrum. When the sub-cells are connected in series in a tandem PSC, the open-circuit voltage ( V OC ) of the sub-cells ideally adds up while the short-circuit current density ( J SC ) is limited by the smallest J SC generated in any of the sub-cells. [ 7,[9][10][11][12] A critical component to produce effi cient tandem PSCs is the charge recombination layer (CRL) that connects the two adjacent sub-cells. The CRL that is sandwiched between the sub-cells, needs to allow holes to be collected from one sub-cell and recombine with the electrons collected from the other sub-cell, while allowing photons to pass through it and illuminate the adjacent sub-cell. Furthermore, the CRL should have low electrical resistance to minimize power density losses. Therefore, materials comprising the CRL are required to have low absorption in the spectral region of interest, be suffi ciently conductive, and provide a large work function (WF) contrast between the two outward surfaces in contact with the photoactive layers. In addition, in tandem PSCs, the CRL also needs to allow for the fabrication of a solution-processed top photoactive layer. [ 7 ] The tandem PSC geometry dramatically impacts the pool of materials available for the realization of effi cient hole and , and a fi ll factor of 0.62 ± 0.01, resulting in a power conversion effi ciency of 6.5% ± 0.1% under simulated AM 1.5G, 100 mW cm −2 illumination.

Interfacial Materials for Organic Solar Cells: Recent Advances and Perspectives

“…Correspondingly, ITOSCs using two complementary absorbing BHJ cells of PCDTBT:PC 71 BM and PDPP3T:PC 71 BM showed a PCE of 7.31%, suggesting high charge collection and recombination efficiencies in a tandem structure with this ICL. Based on a HTL of thermally deposited MoO x , MoO x /Al 2 O 3 :ZnO nanolaminate/PEIE, MoO x /Al 2 O 3 :ZnO nanolaminate, or MoO x /ZnO/PEIE was used as a h‐e‐type ICL for ITOSCs based on two active layers of P3HT:ICBA and PBDTTT‐C:PCBM with complementary absorption ranges Using the highly conductive Al 2 O 3 :ZnO nanolaminate with PEIE modification delivered about 20% higher FF than the ICL containing ZnO modified by PEIE, finally leading to an improved PCE of 6.5% for the ITOSCs with a MoO x /Al 2 O 3 :ZnO nanolaminate/PEIE ICL.…”

Recent Advances Toward Highly Efficient Tandem Organic Solar Cells

“…Many research works have been focused on the all-inorganic ICLs containing MoO 3 hole collection layer, such as MoO 3 /Ag or Al/ZnO, [124,130,139,162] ZnO/Al or Au/MoO 3 , [71,168] MoO 3 /SnO 2 , [74] LiF/Al/MoO 3 , [134] TiO 2 /Al/MoO 3 , [135] and so on, in which the n-type metal oxides served as electron collection layer. Surface modification of these n-type metal oxides (e.g., MoO 3 /Ag/ZnO/ poly[((9,9-bis(3 0 -(N,N-dimethylamino)propyl)-2,7-fluorene)alt-2,7-(9,9-dioctylfluorene)dibromide] (PFN-Br), [103,123] MoO 3 / aluminum oxide (Al 2 O 3 ):ZnO/PEIE, [147] and MoO 3 /Ni/ZnO: poly(2-ethyl-2-oxazoline) (PEOz) [42] ) increased the work function contrast between the two outward surfaces of the ICL, which further improved the performance of tandem OSCs. In addition, to avoid the application of acidic PEDOT:PSS and high thermal annealing process, thermal treatment-free ICLs containing the vacuum-deposited MoO 3 /Ag or Al and water/alcohol soluble organic electrolytes were developed, such as MoO 3 /Ag/PFN, [59,60,80,96,111,113,172,173,183] MoO x /Ag or Al/PFN-Br, [121,180] 2,9-bis(3-(dimethylamino)propyl)anthra [2,1,9-def:6,5,10-d 0 e 0 f 0 ]diisoquinoline-1,3,8,10(2H,9H)-tetraone (PDIN):PFN/Al/MoO 3 , [37] and MoO 3 /Ag/PEIE, [160] MoO 3 /Ag/ titanium (diisopropoxide) bis(2,4-pentanedionate) (TIPD), [174] and so on.…”

Effects of p‐Type Nickel Oxide Semiconductor and Gold Bilayer on Highly Efficient Polymer Solar Cell

“…However, the PCE of the PSCs is still insufficient for these devices to be commercially feasible. Therefore, the development of high‐performance PSCs is imperative, and the production of highly efficient PSCs has been the focus of intensive research . An important research focus in the realization of highly efficient PSCs is the high work function (WF) interfacial physical and electrical contact between the organic and inorganic materials at the bottom of the cell .…”

“…Moreover, the HCI should have a high electrical conductivity to diminish the power losses. In addition, the HCIs should possess large WF value to avoid the formation of a rectifying junction between the HCI and donor material . Thus, the HCI material requires a high optical transparency in the spectral region of interest, a sufficiently large WF value at the surface, and a low electrical resistance to maximize the short‐circuit current density ( J SC ) and to optimize the open‐circuit voltage ( V OC ).…”