A monolithic all-silicon multi-junction photovoltaic electrolysis device for solar hydrogen production by direct water splitting

本提案的目的是基于改进的叉指背接触（IBC）晶体硅（Si）太阳能电池的单片全硅多结太阳能制氢装置的演示、研究和优化，所述太阳能电池是无线的，基于成熟的技术，并因此允许将用于直接水分解的光电解系统的优点与光伏/电解（PV/E）系统。与现有的IBC太阳能电池相比，在本方法中，采用深度显著超过包括耗尽区的掺杂接触的深度的深沟槽隔离（DTI）使每隔一个n-p结彼此绝缘。由DTI绝缘的三个n和p部分通过金属触点串联连接，以产生足够高的光电压，这允许提供1.23 V的水氧化还原电位，同时考虑过电位和损耗。与垂直堆叠的多结（MJ）电池相反，我们的方法具有以下优点：首先，由于没有前侧触点，完全避免了阴影。再加上高质量的硅晶片材料，这导致了高效的太阳能电池。第二，两个触点都在背侧上，因此前侧不与电解质接触，这在前侧的制备中在结构和材料方面提供了更大的自由度，因为完全避免了腐蚀。第三，IBC设计产生太阳能电池的光转换主体和用于电解的触点的分离。因此，与电解质接触的电极可以在背面密封在化学稳定的厚绝缘体中，而不影响太阳能电池的光吸收特性。第四，采用镍硅化工艺来串联连接n和p部分允许具有良好欧姆接触的真正单片MJ实现，这完全避免了布线。因此，Si晶片原则上可以用作电解质容器的密封件，从而产生紧凑、坚固的制氢装置。最后，我们的方法是基于硅太阳能电池，因此在一个无毒和丰富的材料。在第二个设备配置，多孔硅膜实施到MJ-PV/E电池。然而，使用通孔技术，在晶片的两侧上放置接触，使得多孔Si膜可以充当质子交换膜，其允许将器件用作PV/E电池和微型燃料电池。在我们的MJ-PV/E器件在光电流下在AM 1.5G照明下操作的假设下，这是所报道的IBC电池的40.6mA/cm 2的短路电流密度的三分之一，STH ~ 16%的太阳能-氢气转化效率是可行的。在理想条件下，Si太阳能电池可以提供44 mA/cm 2的短路电流密度，产生约19%的最大STH。

The aim of the present proposal is the demonstration, investigation and optimization of a monolithic all-silicon multi-junction solar hydrogen production device based on a modified interdigitated back-contact (IBC) crystalline silicon (Si) solar cell that is wireless, is based on a mature technology, an abundant material and thus allows combining the advantages of a photoelectrolytic system for direct water splitting with the benefits of a photovoltaic/electrolysis (PV/E) system. In contrast to existing IBC solar cells, in the present approach every second n-p junction is insulated from each other employing a deep trench isolation (DTI) with a depth significantly exceeding the depth of the doped contacts including the depletion regions. Three n and p sections that are insulated by the DTI are connected in series by metal contacts to generate a sufficiently high photovoltage which allows to provide the water redox potential of 1.23 V taking overpotentials and losses into account.Contrary to vertically-stacked multi-junction (MJ) cells our approach has the following advantages: First, shadowing is completely avoided since there are no front side contacts. Together with the high quality of the Si wafer material this leads to a highly efficient solar cell. Second, both contacts are on the back side and hence the front side is not in contact with the electrolyte which provides a larger degree of freedom in the preparation of the front side in terms of structure and material since corrosion is completely avoided. Third, the IBC design yields a separation of the light converting bulk of the solar cell and the contacts for electrolysis. Hence, the electrodes that are in contact with the electrolyte can be sealed in a chemically stable, thick insulator at the back side without affecting the light absorption properties of the solar cell. Fourth, the employment of a nickel silicidation process to connect the n and p sections in series allows for a true monolithic MJ implementation with good ohmic contacts, which avoids wiring completely. As a consequence, the Si wafer could in principle serve as the seal of the electrolyte container yielding a compact, robust hydrogen production device. Finally, our approach is based on a Si solar cell and thus on a non-toxic and abundant material.In a second device configuration, a porous Si membrane is implemented into the MJ-PV/E cell. Using a through-via technique, however, contacts are placed on both sides of the wafer such that the porous Si membrane can act as a proton exchange membrane that allows using the device as a PV/E cell and as a micro fuel cell.Under the assumption that our MJ-PV/E device operates under AM 1.5 G illumination at a photocurrent, which is a third of the reported short-circuit current density of 40.6 mA/cm2 of IBC cells, a solar-to-hydrogen conversion efficiency of STH ~ 16% is feasible. Under ideal conditions, a Si solar cell can provide a short-circuit current density of 44 mA/cm2 yielding a maximum STH of ~ 19%.