Charge Transport Properties Of Organic/Inorganic Si Hybrid Solar Cells

This thesis investigated the photovoltaic characterization and charge carrierstransportation mechanism of hybrid Schottky heterojunction solar cell based onnanostructured silicon with different surface morphologies and conductive conjugatedpolymer poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)(PEDOT:PSS). Thesurface/volume ratio of silicon nanowire arrays (SiNWs) was reduced; meanwhile thenanostructured silicon substrates still could ensure a good light absorption, a reducedsurface charge recombination velocity, and a minimized surface trap states density,which was vital to high performance solar cell. The Si/PEDOT:PSS organic-inorganichybrid heterojunction solar cell, and achieved a high power conversion effic iency(PCE) of13.6%. Reflection spectrophotometer with integrating sphere, transmissionelectron microscope (TEM), scanning electron microscope (SEM), minority chargecarriers lifetime detector, inductively coupled plasma mass spectrometry (ICP-MS),transient photovoltage decay, numerical simulation, etc., were used to characterize thesolar cell’s performance, charge carriers transportation mechanism, different surfacemorphologies, flexible silicon substrates, and different materials modificationsystematically. The main work includes:1. Interface properties of Si/PEDOT:PSS hybrid photovoltaic (PV) devices wereinvestigated. The surface trap states density which could influence the chargeseparation, transportation, and device performance, was characterized. The surface trapstate density was influenced by the surface morphology of the silicon solar cell, thedevice based on methylated SiNWs showed a higher PCE than those devices based on unmethylated SiNWs and methylated planar silicon substrates, because the devicesbased on methylated SiNWs contained a low surface trap state density of~1012cm-2eV-1, which was lower than that of traditional metal-semiconductor Schottkyheterojunction solar cell (1013-1014cm-2eV-1). The quality of heterojunction wasimproved effectively.2. The organic-inorganic hybrid Schottky heterojunction solar cell with a PCE of12.1%was fabricated to study the influence of series resistance and shunt resistancetuning effect on the solar cell performance. It was found that the variation of seriesresistance and shunt resistance could influence the performance of device dramatically,indicating that the suitable silicon substrate size and physical tailoring method could beused to effectively control the series resistance and shunt resistance, that couldimprove the device performance accordingly.3. Low-temperature solution-processed method was introduced to fabricatehybrid Schottky heterojunction device based on upgraded-metallurgical grade (UMG)silicon substrates. Metal assisted chemical etching (MACE) method could partiallyimprove silicon quality near the surface of the silicon substrate to suppress theShockley-Read-Hall (SRH) recombination. Meanwhile, the nanostructured siliconsubstrate could compensate the inferior light absorption ability of thin siliconsubstrates, improving the device performance, and reducing the requirement ofhigh-purity silicon material. The UMG Si/PEDOT:PSS hybrid Schottky heterojunctiondevice and achieved a record PCE of12.0%.4. Ultrathin (~14m) flexible nanostructured silicon substrates with simplesurface modification were prepared and used to fabricate organic-inorganic hybridheterojunction solar cells, achieving a PCE of9.1%. In order to enhance theinsufficient light absorption ability of ultrathin silicon substrate, the siliconnnanostructures were fabricated by MACE method. As a result, the light absorptionwas improved by60%than that of the planar ultrathin silicon substrate.5. High efficient hybrid Si/PEDOT:PSS heterojunction solar cells withroom-temperature solution-processed ZnMgO nanocrystal film as hole blocking layer were fabricated, exhibiting a high PCE of13.6%. The ZnMgO nanocrystal films werespin-coated on the rear side of solar cell to form a hole-blocking layer. The holeblocking layer could not only prevent hole from diffusing into cathode, but alsoimprove the contact recombination problem at the rear electrode by suppressing thecharge recombination and improving the charge transport.