Tuning back contact property via artificial interface dipoles in Si/organic hybrid solar cells

Abstract

Back contact property plays a key role in the charge collection efficiency of c-Si/poly(3,4-ethylthiophene):poly(styrenesulfonate) hybrid solar cells (Si-HSCs), as an alternative for the high-efficiency and low-cost photovoltaic devices. In this letter, we utilize the water soluble poly (ethylene oxide) (PEO) to modify the Al/Si interface to be an Ohmic contact via interface dipole tuning, decreasing the work function of the Al film. This Ohmic contact improves the electron collection efficiency of the rear electrode, increasing the short circuit current density (Jsc). Furthermore, the interface dipoles make the band bending downward to increase the total barrier height of built-in electric field of the solar cell, enhancing the open circuit voltage (Voc). The PEO solar cell exhibits an excellent performance, 12.29% power conversion efficiency, a 25.28% increase from the reference solar cell without a PEO interlayer. The simple and water soluble method as a promising alternative is used to develop the interfacial contact quality of the rear electrode for the high photovoltaic performance of Si-HSCs.

Passivating contacts for crystalline silicon solar cells

“…The use of small organic molecules or self-assembled monolayers have been comparatively more successful. On silicon, materials like poly (ethylene oxide) (PEO) 120 and 8-hydroxyquinolinolato-lithium (Liq) 121 have been shown to reduce barrier heights and facilitate improvements in electron collection. Recently, monolayers of polar amino acids have also been shown to facilitate electron collection following direct Al metallisation on silicon, with an efficiency of 17.5% having been demonstrated utilising this contacting approach as a full rear contact on an n-type Si wafer.…”

Polymeric Electron-Selective Contact for Crystalline Silicon Solar Cells with an Efficiency Exceeding 19%

“…Several types of organic molecules have been demonstrated as ETLs for c-Si cells, such as PEO (poly(ethylene oxide)), Liq (8-hydroxyquinolinolato lithium), CPTA (C 60 pyrrolidine tris-acid) and amino acids, among which L-histidine, an amino acid, is used as an electron-selective contact of c-Si(n) cells with a PCE of 17.9%. [21][22][23][24][25] Common to all of these devices is a relatively low open-circuit voltage (V oc ), due to poor surface passivation, which hinders the PCE of hybrid organic/c-Si solar cells with organic ETLs. The search for an organic ETL that is compatible with a well-passivated c-Si architecture (e.g., SiO 2 /c-Si, a-Si:H/c-Si) has been elusive to date, motivating the present work.…”

“…As for the electron-selective contact, a simple, directly metallized c-Si­( n )/Al contact is well-known to exhibit a large energy barrier for electrons as well as severe carrier recombination because of the high concentration of surface defects, including metal induced gap states. − Therefore, an efficient electron-selective contact is also required in the design of hybrid organic/c-Si solar cells. Several types of organic molecules have been demonstrated as ETLs for c-Si cells, such as PEO (poly­(ethylene oxide)), Liq (8-hydroxyquinolinolato lithium), CPTA (C 60 pyrrolidine tris-acid), and amino acids, among which l -histidine, an amino acid, is used as an electron-selective contact of c-Si­( n ) cells with a PCE of 17.9%. − Common to all of these devices is a relatively low open-circuit voltage ( V oc ), due to poor surface passivation, which hinders the PCE of hybrid organic/c-Si solar cells with organic ETLs. The search for an organic ETL that is compatible with a well-passivated c-Si architecture (e.g., SiO 2 /c-Si, a-Si:H/c-Si) has been elusive to date, motivating the present work.…”

Effect of Thermal Annealing on the Charge Carrier Selectivity of Ultra‐Thin Organic Interface Dipoles in Silicon Organic Heterojunction Solar Cells

“…[ 58–65 ] In particular, organic molecules with a strong permanent dipole moment can change the band alignment at the interface and, thus, the charge carrier selectivity by modifying the concentration of charge carriers in the vicinity of the electrode contact. In the past dipole materials such as 8‐hydroxyquinolinolato‐lithium (Liq), [ 66,67 ] polyethyleneoxide (PEO), [ 68 ] poly[(9,9‐bis(30‐( N , N ‐diethylamino)propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)] (PFN), [ 69 ] perylene diimide (PDIN), [ 70 ] buckminsterfullerene (C 60 ) doped by tetrabutylammoniumiodide (TBAI), [ 71 ] poly[4,8‐bis(2‐ethylhexyloxyl)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl‐alt‐ethylhexyl‐3‐fluorothieno[3,4‐b]thiophene‐2‐carboxylate‐4,6‐diyl] (PTB7)‐based conjugated polyelectrolytes, PTB7‐NBr and PTB7‐NSO3, [ 72 ] quinhydrone (QHY), [ 73 ] and branched polyethylenimine (b‐PEI) [ 41 ] were applied as ultra‐thin interfacial layers to form electron‐selective contacts. In addition, the amino acid l ‐histidine was investigated as an electron‐selective contact, enabling promising contact properties.…”