For example, Ti 3 C 2 T x with sizes ranging from quantum dots level (below 10 nm) [12] to microscale (lateral dimensions of a few micrometers) [13] based on low-temperature liquid processing have been fabricated and they have been used for different applications, such as biological imaging, [12] supercapacitors, [14,15] and batteries. [16,17] In addition to these applications, transparent conducting films/electrodes with thicknesses ranging from 5 to 70 nm [18] and figure of merit as high as 15 [19] have also been prepared based on Ti 3 C 2 T x flakes using different fabrication processes, including drop casting, [20] spin coating [21] and spray coating. [18] Given their high electrical conductivities, such films have substantial potential to replace the traditional expensive transparent conducting electrodes in a wide range of electronic and optoelectronic devices, such as transistors, [22] supercapacitors, [19] photodetectors, [20] and solar cells. [23,24] From the point view of energy conversion, the photovoltaic (PV) response observed in the case of a photodetector created by MXene/Si heterojunction shows the realistic potential of Ti 3 C 2 T x as an electrode in solar cells. Furthermore, it has been theoretically shown that the work function of Ti 3 C 2 T x can potentially be tuned from less than 2 eV to above 6 eV by precise control over the termination groups. [25] This shows great promise to use the Ti 3 C 2 T x electrode to tune the barrier height. Therefore, the efficiency of charge separation at a solar cell junction formed between the MXene and a semiconductor of a proper bandgap such as silicon (Si) can be improved, in addition to fulfilling the requirements as a transparent conducting electrode. [26] Although the use of MXene in a wide range of applications is well documented, studies on the exploration of MXene in photovoltaics have been very sparse to date. Very recently, Yang et al. [27] have demonstrated low-temperature perovskite solar cells with high efficiency and small cell-to-cell variations using solution-processed Ti 3 C 2 /SnO 2 nanocomposites as the electron transporting layers. The high conductivity of MXene has been found to effectively improve the charge extraction and transfer, and thus resulted in higher photocurrents. These findings clearly indicate the great potential of MXenes in solar cells. However, to the best of our knowledge, no attempt has been made to employ MXenes as an active component in a photovoltaic device. Inspired by the previous success in carbon nanotube/Si [28] and graphene/Si [29] heterojunction PV cells with high power A novel type of solar cell has been developed based on charge separation at the heterojunction formed by a transparent conducting MXene electrode and an n-type silicon (n-Si) wafer. A thin layer of the native silicon dioxide plays an important role in suppressing the recombination of charge carriers. A two-step chemical treatment can increase the device efficiency by about 40%. Promisingly, an average power conversion efficiency of over 10% un...