利用掃描穿隧顯微鏡量測鈣鈦礦太陽能電池晶粒的光致電子特性

Abstract

鈣鈦礦太陽能電池(Perovskite solar cell, PSC)除了其製程的快速、便利性外，其備受矚目的便是極高的光電轉換效率。有研究發現鈣鈦礦反應層可藉由摻雜量子晶體來影響光電轉換效率。目前已有團隊利用摻雜量子晶體硫化鉛改良鈣鈦礦太陽能電池的效率。研究成果發現，藉由添加硫化鉛有助於增加晶粒的形貌大小，此外還有效地提升太陽能電池的光電轉換效率。 本研究利用掃描穿隧顯微鏡進行量測太陽能電池的主動反應層甲胺鉛氯碘鹽(CH_3 NH_3 PbI_(3-x) 〖Cl〗_x)添加量子晶體後的電子特性的變化。同時比較摻雜硫化鉛及未摻雜硫化鉛後反應層的變化，並針對加光前後的能態密度在正負偏壓增減的情形進行能帶討論。實驗結果顯示摻雜硫化鉛的鈣鈦礦反應層薄膜晶粒直徑變大，且其在加光過後的費米能階遠離導電帶的能量變化量值較未摻雜硫化鉛的樣品晶粒較大，顯示光致載子在鈣鈦礦反應層薄膜分離效率更好，進而導致其光電轉換效率提升。

The recent studies show that intermixing quantum crystal PbS with the active light-absorber (〖CH〗_3 〖NH〗_3 〖PbI〗_(3-x) 〖Cl〗_x) film in perovskite solar cell enlarges the grain size, which can be exceeded to 4µm. The quantum crystal in perovskite increases not only power conversion efficiency over 17.4%, but also the diffusion length. In order to investigate the variation of the electronic properties of the perovskite solar cell film in dark and under illumination condition, scanning tunneling microscopy (STM) was utilized to study the topography images and localized electronic properties of the perovskite active light-absorber. In this work, the electronic dI/dV spectroscopy measurement of perovskite intermixing PbS in dark demonstrates n-type semiconductor behavior. Moreover, the increase of density of states at valence band of perovskite film reveals the augment of hole carrier concentration under illumination. The shift of electronic dI/dV spectroscopy of perovskite with PbS compared to that of the perovskite without PbS shows that the magnitude of carriers separation is associated with the grain size. Also the grain size enlarged is beneficial for power conversion efficiency (PCE).