Study On The Interface Problem Of Organic-Inorganic Hybrid Solar Cells

With the continuous decrease of global fossil energy and the increasingly serious environment problem, solar energy as a kind of clean renewable energy has attracted more and more attention. Solar cells can directly convert solar energy into electricity through the photoelectric effect, which is an ideal way of solar energy utilization. Organic-inorganic hybrid solar cell, as a new type of photovoltaic cells, combined with the characteristics of the organic material and inorganic material, is expected to become a kind of low-cost, highly efficient and flexible photovoltaic cells. However, the photoelectric conversion efficiency of such hybrid cells is still relatively low, and the interface problem is one of the main reasons which restrict the efficiency:The two-phase interface shows poor performance because of the differences between silicon materials and organic polymer; there is usually a large number of dangling bonds on the surface of crystalline silicon leading to serious recombination of minority carriers. Such interface problems will lead to poor separateion of carriers at the interface. Therefore, it is of great significance to study and improve the interface properties for enhancing the performance of organic-inorganic hybrid solar cells, and promoting the industrial production and commercial application of such hybrid cells.Based on that, we first prepared ultra-thin flexible silicon wafers by KOH chemical etching, next we fabricated planar monocrystalline silicon/PEDOT:PSS organic-inorganic hetero-junction hybrid cells based on silicon substrates of 525μm and 18μm, with conjugated conducting polymer PEDOT:PSS as an organic hole transport layer. Then we studied the interface problem of the hybrid cells mainly from two aspects:the optimization of interface contact of silicon/PEDOT:PSS and the realization of effective passivation on the surface of monocrystalline silicon. The main research work is as follows:Research has been carried out on the interface contact optimization and its effect on the performance of hybrid devices. Through the incorporation of fluorine surfactant FSH into the PEDOT:PSS, contact angle of the silicon/PEDOT:PSS decreases by nearly 60%, greatly improveing the infiltration of PEDOT:PSS on the surface of the silicon; besides, through the regulation of spin-coating speed of PEDOT:PSS mixed solution, we have got the best performance of hybrid cells at the speed of 3000 r/min, for PEDOT:PSS film on monocrystalline silicon shows the best quality; in addition, using atomic force microscope scanning the surface topography of monocrystalline silicon before and after etching thinning, we have found that the root mean square (RMS) of the surface roughness of ultra-thin silicon wafer is about 10 times of that of thick silicon wafer, leading to a sharp increase of the contact aera between surface of thin silicon wafer and PEDOT:PSS film, being benefit to carrier separation at the interfaces thus reducing the interface contact resistance effectively, therefore hybrid solar cells based on the ultra-thin silicon wafers possess lower series resistance higher filling factor as well as greater ratio of measuring short circuit current density to the theoretical limit current density.The passivation effect on the surface of monocrystalline silicon and the performance of hybrid cells has been compared among three passivation methods: natural oxidation (NO), hydrofluoric acid (HF) treatment and inserting intrinsic amorphous silicon (if a-Si) layer. By measuring minority carrier lifetime of the silicon passivated by above methods, we have calculated the corresponding surface recombination velocity of the monocrystalline silicon. The higher the surface recombination velocity is, the better the passivation effect is, thus the higher short circuit current density of hybrid cells can be obtained. By controlling the time of natural oxidation or the deposition temperature of amorphous silicon, we have obtained the best natural oxidation time as 12h and the best deposition temperature of amorphous silicon as 250 degrees Celsius. By comparison, i a-Si passivation gives the best effect, leading to the highest efficiency of thick silicon and thin silicon based hybrid cells as 9.78% and 5.68% respectively with the highest short-circuit current density; then is the HF-treated method and then is the natural oxidation method. This trend is consistent for thick silicon based and thin silicon based cells.